A supreme technical document dedicated to the world's potters: Kano Mitsuo's Notes (Forming, Silver Glaze, Shoji Hamada and Kanjiro Kawai's Secret Recipes)
Welcome to Antique Liquor 1926. We deliver the essence of modern Japanese beauty and traditional craftsmanship, passed down through time, to the world.
We are pleased to announce the systematic organization, reconstruction, and full release of the handwritten pottery notes by Kyoto master potter Mitsuo Kano, which have been carefully preserved in our gallery archive. This document meticulously records extremely valuable primary information in the history of Japanese pottery, ranging from decades of trial and error in clay blending, to techniques for preventing exfoliation in Ko-Kutani ware, methods for replicating artificial iridescence, and even the secret glaze recipe directly imparted by the late Kanjiro Kawai in 1943.
Our purpose in releasing this vast technical heritage is singular. It is to provide a solid foundation for potters, craft researchers, and collectors who love beauty, not only in Japan but around the world, who strive to create pottery, using this "crystallization of knowledge" that our predecessors built by dedicating their lives to fire and earth. We could not be happier if this document serves as a new source of inspiration and technical advancement for all creators who weave beauty across borders.
Preface
I have been contemplating this for many years, but it has yet to come to fruition. I wish to record the progress of my pottery, which I have continued for several decades, however clumsily. While it may not end in a three-day monk-like fashion, I intend to write it as time permits. I hope it will be of some use after my death, but it may also just end up as a laughing matter. Please forgive any lack of chronological order in the content, as I will be writing it as memories come to me.
November 29, Showa 40 (1965), Mitsuo Kano
Chapter 1: The Origins of Pottery and the Primitive Beauty of Form
While the origin of pottery should be left to the research of specialists, if I were to offer my own thoughts, its beginning traces back to "earthenware." Humans walked on muddy ground softened by rain, leaving footprints that then hardened as the sun dried the indentations. It is likely that human intelligence derived the idea of "creating shapes" from this phenomenon. Furthermore, strong winds would cause trees in primeval forests to rub against each other, generating heat and igniting large fires. After the fire subsided, a hard, compact ground, different from before, would form. I believe that the combination of these two phenomena – "shaping" and "heat application" – is precisely the origin of pottery.
The detailed beginnings of all things are beyond my area of expertise and thus uncertain, but there is no doubt that the history of pottery is extremely ancient. The same can be said for how humanity began to settle on the earth. Humans, possessing the characteristic of "thought," not merely hunted for survival but also devised various innovations, eventually leading to the creation of pottery as a familiar household item. However, the invention of the technology to artificially create fire itself must have been an undertaking comparable to modern humans building a hydroelectric power plant.
So, how did humans, having acquired the techniques of shaping and fire-making, fire their pottery? I once heard about the manufacturing method when an American acquaintance gifted me a piece of earthenware made by Native Americans. They would arrange objects on a bed of dry grass, then layer more grass, stacking them alternately in a circle, and ignite it from the periphery. The rising hot air would create a draft, causing vigorous combustion and firing the earthenware. It is believed that similar firing methods are still practiced among people who live primitive lives today.
Ancient earthenware possesses an inherently strong and captivating charm. All its forms are bold and expansive, and the applied patterns are positioned appropriately. This is precisely because they were created purely as tools for their own lives, without concern for others, and the maker's subjective vision is honestly realized.
Chapter 2: Craft Beauty and Reflections on Modern Technology and Materials
Over its long history, methods of shaping and design, as well as firing techniques, have made remarkable progress. In the field of industrial production, the development of mechanization and chemical technology has been remarkable, approaching a state of perfection. However, from a craft perspective, it cannot be denied that excessive analysis and rationalization can, conversely, harm the aesthetic essence.
The most crucial aspect of a craft piece is the understanding and respect for its "material." Just as a master chef cannot create a great dish with poor ingredients, so too can inferior materials not exceed a certain limit, no matter how much skill is applied. The fundamental principle is to accurately bring out the characteristics of the material and elevate them into one's own expression, or to select the optimal material according to the desired form. Maintaining this perspective while critically incorporating modern chemical technology and mechanical methods is the logical approach required of contemporary makers.
When I encounter drawings and crafts made by young children, I am sometimes deeply moved by their honest sensibility and the strength of their pure, intuitive expression. The beauty found in primitive artifacts is of the same quality. As civilization advances, techniques become more complex and formalized, and the ability to evoke emotion in people tends to diminish. This is precisely where the struggle of craftsmanship lies, but my personal ideal is to deeply explore acquired knowledge and techniques, then deliberately "set them aside" and return to a childlike, primitive spirit to immerse oneself in the work.
Chapter 3: Classification of Clay Bodies and the Character of Clay from Various Regions of Japan
The characteristic components of clay bodies are broadly classified into three main elements: "clay minerals," "feldspathic materials," and "silica (quartz)." Some also contain auxiliary components such as lime, talc, and titanium.
i. Porcelain and Special Porcelain: There are bone china, which contains a considerable amount of bone ash; calcareous porcelain, which has limestone added to harden at low temperatures; and special porcelain, which has talc and titanium added to harden at SK7-8. These are not common for craft purposes. Those primarily composed of kaolinite and other high-alumina clays, fired to a high degree of vitrification at around SK14, are called "hard porcelain" and boast the highest hardness.
ii. Earthenware, Stoneware, and Coarse Earthenware: These refer to clays with a high proportion of clay minerals, gradually transitioning to a porcelain-like quality as the proportion of feldspathic materials increases. The hardness of the body is highest with kaolinitic hard porcelain, followed by feldspathic porcelain, earthenware, stoneware, and coarse earthenware. However, there are exceptions, such as Tokoname's shu-dei (red clay) and titanium porcelain, which are stoneware but exhibit hardness exceeding that of hard porcelain. Calcareous porcelain and porcelain with excessive feldspar have the drawback of being prone to cracking under rapid temperature changes.
For earthenware bodies in Kyoto, Shigaraki clay is the most widely used due to its geographical convenience, ease of forming, and suitability for firing at SK8-10. Iron-bearing clays are scattered throughout Japan, but for raw clays that have excellent plasticity like roof tile clay but low refractoriness, chamotte or Kibushi clay, etc., are blended to adjust the refractoriness. Tokoname's shu-dei body is a naturally weathered elutriated clay similar to roof tile clay, rich in iron and excellent in formability.
Bizen ware bodies are rich in quartz and have superior refractoriness, but because they contain organic matter and iron, they are prone to "buku" (blistering) due to rapid heating. Therefore, slow and gradual firing is required. Unglazed wares with a water absorption rate of 1% or less are classified as stoneware, and structures that heat up slowly, such as electric kilns, are more effective in suppressing the occurrence of buku.
The "hiero" (fire color) that appears on unglazed bodies is a phenomenon where alkaline components in the body volatilize at high temperatures and react with quartz to form a thin natural glaze film (similar principle to salt glaze), and the iron content acts to produce color. Bizen's "hi-tasuki" (fire cords) also operates on this principle, where vibrant fire colors can be artificially obtained by wrapping straw (siliceous) soaked in saltwater around the ware. Fire colors appear most beautifully in wood-fired kilns. Karatsu, Mashiko, and Ko-Tanba bodies are rich in iron and sand, while Shino, Oribe, Kiseki, and Hagi bodies have coarse particles and are high in kaolinite, all indicating that they were fired at considerably high temperatures in their heyday.
The clay bodies of Nonomura Ninsei and old Satsuma ware are similar to Shigaraki clay, but with slightly less iron. In Kyoto ware, Shirakura clay and Mishishi powder are added to Shigaraki clay to prepare Ninsei body. Old Satsuma is rich in alumina, resulting in fine crazing, and has the characteristic of being hard-fired and resistant to staining.
Ceramic (stoneware) production areas include Kyoto, Arita, Izushi, Kutani, Seto, Aizu, and Tobe. In Kyoto, until the early Taisho period, a body slurry composed of 60-70% Amakusa stone and 30-40% Shigaraki clay was used. Amakusa stone alone can produce porcelain without crazing, but clay is added to supplement its plasticity.
Chapter 4: Clay Body Preparation and Traditional Refining Techniques
For the preparation of clay bodies, it is advisable to entrust fine porcelain (stoneware) to specialized pottery material companies with well-equipped facilities. For earthenware (pottery), however, drying and crushing raw clay collected from mountains and then blending it yourself can sometimes result in unique and rustic charm after firing. The traditional belief is that storing prepared clay for an extended period to "age" it promotes the decomposition of organic matter, increases plasticity, and prevents cracks and distortions during drying and firing.
In the early Taisho era, the traditional refining process for earthenware bodies in Kyoto was as follows: Dry raw materials were added to a barrel of water and stirred, then passed through progressively finer sieves as clogging occurred. After removing the supernatant water from the sediment (yabukuma), the slurry was poured into unglazed pots wrapped with rope, or into framed structures with gaps between planks and mats lining the inside, for dewatering. Alternatively, slurry was placed on unglazed "makura" (bricks), and makura were stacked alternately to absorb excess moisture and dewater, adjusting the clay to a suitable hardness for forming. While these ancient methods produced extremely high-quality clay bodies, modern mechanical grinding using ball mills (trommel mills) pulverizes even the sand particles, thus altering the clay's inherent rustic qualities.
Porcelain (stoneware) scraps and waste require re-processing through elutriation, as it is difficult to remove minute air bubbles within them. In the self-elutriation method, common until the early Showa era, crushed stone was added to water in a barrel, stirred, and passed through an extremely fine sieve of 120 or 150 mesh (120 mesh was called "kinu-habutae tōshi," or silk habutae sieve). The resulting slip was placed in a thick cotton cloth bag and dewatered uniformly using wooden boards and weights, or a screw press, then reused as clay of appropriate hardness.
Chapter 5: Slip Application, Glazing Techniques, and the Practice of Bisque Firing
【When applying slip and glaze to "greenware" (unfired clay)】
Unless there is a need for raw glazing (applying glaze directly to greenware after forming and drying, without bisque firing), it is generally easier and more convenient to bisque fire once. Glazing greenware (porcelain) is relatively safe. Still, care is required in handling due to the inherent fragility of the body itself. However, for large pieces that are prone to cracking during bisque firing due to rapid temperature increases, raw glazing is often safer.
On the other hand, for earthenware, applying slip to greenware is often more convenient and results in a better finish. If earthenware is completely dried, there is a risk of damage due to rapid water absorption during glazing, so caution is necessary. The most suitable time is just before complete dryness, when the clay body's shrinkage has ceased. While thick pieces may not pose much of a problem, greenware can expand by absorbing water (ichi-hari) or, if glazed while still damp, the glaze may peel off (exfoliate) or crack during the drying process or due to shrinkage of the body. Therefore, utmost care is essential. Especially when glazing the inside of "bag-shaped" items such as jars and vases (uchigake), it is even more critical to accurately assess the dryness of the clay body.
Furthermore, when applying glaze with a brush, it is better to do so after the body is thoroughly dried. It is safe to mix funori (seaweed paste) into the glaze and apply it in several layers, allowing each layer to dry in between.
I hear that in Jingdezhen, China, a major traditional production center for porcelain, all works are made by raw glazing. Observing the areas where the glaze has been scraped off the footring, one can see this characteristic. Celadon glazes also appear to be applied thickly by layering them multiple times. I once witnessed Rokuro Shimizu III mixing funori into his glaze and applying it in several layers, allowing each to dry. Also, if a glaze is of a type that sets by bisque firing, it is a good technique to bisque fire once and then apply further layers. Indeed, I tried this with Kyoto Pottery Company's No. 1 lime glaze, applying it after bisque firing, and it was perfectly feasible. While spray glazing offers the advantage of uniform application, for glazes that require thick application, there is a tendency for them to run (drip) during firing. Ladle application and brush application are the least prone to glaze runs, with dipping and pouring being next in stability.
Regarding the glazing of Shino ware, I was once taught by my predecessors that "it must be raw glazed." Personally, I sometimes wonder if bisque firing would also be acceptable, but perhaps bisque firing hardens the alkaline components in the clay body, preventing them from seeping to the glaze surface after glazing, and thus impairing the beautiful "fire color" characteristic of Shino ware. This is especially true for Akajino (red Shino), where the rich fire color is its greatest feature.
In a way, skillfully utilizing the unique characteristics of materials can bring taste and charm to a work. As a mindset for pottery making, it is essential to always bring out the best in the materials.
In the East, particularly in China, many excellent pottery pieces have been made using molds since ancient times. While I leave it to specialists to determine whether molds were used before the Han dynasty, it is easy to imagine that the bronze casting techniques of the Han dynasty were applied to ceramic "clay molds." Or perhaps it goes back even further into antiquity.
Mold forming is thought to have originally begun with the mass production of many identical shapes, yet even in forms created without conscious intent, there is a beauty that captivates the modern mind. Even with mold forming, there are many instances where the warmth of handcraftsmanship and the inherent beauty of the material remain undiminished. Molded forms evoke a different dimension of beauty than coil building or wheel throwing. Extremely fine masterpieces remain among the burial goods of the Tang dynasty, such as mingqi (earthen figures), Tang sancai, and blue glazes. Furthermore, surprisingly many jars and similar items were made by clay molding, and in the Song dynasty particularly, I am deeply impressed by the works imbued with a wonderful aesthetic sensibility.
【About Bisque Firing】
For small earthenware pieces, there is no need to be overly meticulous, but for larger works, great care must be taken during the heating process (how heat is raised). It is a prerequisite that the work is completely dried beforehand. While sometimes pieces are dried by holding them over a fire, it is safer to allow them to dry thoroughly naturally before firing. For thin pieces, heat is transmitted uniformly throughout during heating, but for large, thick pieces, it is difficult to maintain uniform temperature between the core and the exterior, so they must be heated slowly and gradually over time (slow heating). In the initial stage of firing in a wood kiln, when the pieces are covered in steam (moisture) and steamed, turning black with soot, is the most critical period. At this stage, do not be complacent and increase the temperature too rapidly. The stage for serious temperature increase begins after most of the moisture has escaped. Specifically, controlling the temperature increase in the range from around 230-250°C to just over 700°C is extremely important. Particular care must be taken with thick porcelain (stoneware) or large pieces with flat bottoms, as they are prone to breakage. Pieces made with coarse clay generally have a certain heat resistance, but even for these, thick pieces should be completely dried before bisque firing. The standard bisque firing temperature is generally around 700-750°C.
Chapter 6: Systematic Classification and Practice of Forming Techniques
【About Forming】
The techniques for shaping clay are flexible depending on the purpose, but the main methods currently used can be broadly categorized as follows:
・Coil building (hand-pinching)
・Coil building + paddle finishing
・Wheel throwing
・Press molding
・Slip casting
・Metal mold, machine wheel forming
【Coil Building (Pinched Forming)】
This is the most widely practiced technique for beginners in pottery. While it is somewhat difficult to create perfectly round or linear forms, it allows for free changes in shape. It has the advantage of generally producing fewer distortions in shape and being less prone to cracks during drying and firing. A slab (tatara) is made by patting clay with the palm to form the base, then long, thin coils of clay are rolled between the hands and stacked in a spiral (wa-zumi) to build up the desired height and shape, after which the surface is smoothed by scraping. Ancient earthenware, including Japan's Jomon and Yayoi pottery, was almost exclusively made using this coil building technique. For larger vessels, there is also a technique where the rough shape is built up using coils and then finished by tightening it with a traditional method called "tataki" (paddling).
【Paddling (Tataki) Forming Method】
This method is primarily used for making large jars and pots. First, the general shape is built up with coils and the surface is smoothed. Then, while gauging the dryness of the clay, the piece is clamped between a paddling tool on the inside and outside, and as the piece is rotated and moved back, it is paddled from the bottom upwards. The tools used include unglazed supports and wooden paddling boards (see diagram). If grooves or other irregularities are carved into the surface of the paddling board, it prevents the damp, soft clay from sticking to the board and becoming difficult to remove. Furthermore, the patterns of these irregularities on the paddling board can be directly transferred to the surface of the vessel, sometimes creating unintended yet excellent decorative effects. If a rope is wrapped around the paddling board and used for paddling, a vivid "jōmon" (rope pattern) is formed. This technique is commonly seen in many jars from the northern Korean Peninsula and ancient Japanese earthenware. Such paddling techniques are widely observed across the world during the early stages of primitive pottery. Large jars from Ryukyu and old Shigaraki also show that coil building, with or without paddling, has been widely used in various regions. It is uncertain whether it is still passed down today, but in the vicinity of Izumo in the San'in region, there is a very interesting traditional technique for raising water jars and similar items. A base is made on a workbench, extremely thick and long coils of clay are wound from the shoulder to the arm, and the vessel is built up. Wooden trowels are applied to the inside and outside, and the worker moves backward while smoothing the wall thickness uniformly and raising the piece. While I myself have no experience, it is a highly skilled technique requiring great proficiency, and the finished vessels boast a magnificent perfectly round shape, achieving a precise finish as if thrown on a potter's wheel.
The coil building technique is also used in Shigaraki for making water jars, but here, a kick wheel is used in conjunction, and with each addition of a thick coil, the height is increased by about 3 sun (approx. 9 cm). This also requires considerable skill, but I once had the opportunity to try it. After building up to a certain height, a damp cloth is used to smooth the inside and outside, and a trowel is applied to the inside to adjust the thickness while extending the clay. This process is repeated, waiting for the clay to firm up to an appropriate hardness before extending it further. This is how large, desired forms are uniformly shaped. In the traditional production of jars and bowls in Naeshiro-gawa, Kagoshima Prefecture, a kick wheel is used. First, wood ash for release is scattered in the center of the wheel head, the clay for the base is pounded on, and then thick coils are stacked and extended. Similar to the aforementioned technique, a damp cloth is applied to the inside and outside to generally smooth it, and a trowel is pressed against the outside while extending to finely adjust the thickness and form. Thus, even with the same coil building, depending on whether the paddling board or trowel is applied from the inside or outside, the expression and texture of the finished vessel change significantly.
【About Wheel Throwing】
The exact origin of the potter's wheel as a tool for ceramics is uncertain. However, given that many ancient earthenware pieces are round, it can be inferred that when coil building, work was done on a flat surface, such as a stone slab. Since it is far more efficient for the platform itself to rotate smoothly than to work on a fixed platform, it is thought that the concept of the "potter's wheel" arose naturally.
In modern Japan, the mechanization of factories and workshops is advancing, and traditional hand-powered potter's wheels are gradually disappearing. However, when observing a slowly and smoothly rotating wheel come to a silent stop, it evokes a warmth, almost like a living being, rather than a mere inorganic tool, and a sense of ineffable nostalgia.
Potter's wheels are broadly divided into "hand wheels," which are rotated by hand, and "kick wheels," which are rotated by kicking with the feet. In traditional Chinese techniques, hand wheels are prevalent, while kick wheels have generally been used in Korean peninsula traditions. I am not familiar with the details of historical Western tools, but they are generally thought to be of the kick wheel type. Bernard Leach also used a kick wheel in the early days of his stay in Japan. However, since he acquired his pottery skills in Japan, this cannot be definitively stated as representative of traditional Western specifications.
The hand wheel (Fig. ①) belongs to the Chinese tradition and has been favored in kilns in Kyoto and Seto since ancient times. On the other hand, kick wheels are dominant in the Kyushu region, Hagi, the San'in region, and Kutani. In Tanba-Tachikui ware, a special structure (Fig. ③) is used where the lower rotating plate is larger than the upper plate. When actually tried, the inertia causes the rotation to last for a long time, making it extremely convenient for continuous production of small items. The direction of rotation for forming (pulling up clay) is always "left-hand (counter-clockwise)," but for trimming the footring with a kick wheel (keburi), it is rotated "right-hand (clockwise)."
Both hand wheels and kick wheels are in danger of disappearing amidst the wave of mechanization, but both possess irreplaceable craft appeal. Especially in forming matcha bowls using a kick wheel, the natural rhythm created by the gradual deceleration and stopping of the rotation as the leg kick changes. The delicate expressions and nuances of the finger marks etched during that change in rotation are incomparable to an electric motor wheel that rotates at a constant speed. Of course, modern electric wheels have also undergone technological improvements, making speed control easier. However, the fact that they constantly rotate at a uniform speed has a somewhat inorganic feel from the perspective of the "aji" (flavor/character) of handwork. However, this can be controlled to some extent by the skill and touch of the craftsman. Especially for large amounts of clay pulling and extending the body, the power and stability of the electric wheel are very welcome, and for this process, nothing surpasses the electric wheel. It is most logical to understand the advantages of both and use them in combination.
Therefore, in my own studio, I always place a kick wheel right next to the electric wheel and use them according to the nature of the work.
【About Mold Forming (Press Molding)】
The technique of using molds in pottery also has a considerably ancient history. In the East, it is thought that molds were utilized earlier in the field of metal crafts than in ceramics, and their origin can be seen in the casting of ancient coins. Furthermore, considering the existence of low-fired earthenware figurines (faience, etc.) in ancient Egypt and its surroundings, it seems that the history of potters using molds began much earlier in the West and Middle East than in the East. Leaving such historical considerations to specialized researchers, utilizing molds in pottery is extremely significant for discovering the unique beauty and formal characteristics inherent to mold forming. Various mold forming techniques have been passed down since ancient times, but with ingenuity, there is still room to create even more innovative and excellent techniques. In contemporary craft settings, "molds" generally refer to plaster molds (here referring to handmade craft applications, excluding industrial metal molds), but before the widespread use of plaster molds, "clay molds" (fired clay molds) were prevalent.
【Example of a Specific Technique Using Molds】
Clay is flattened into a uniform slab (tatara) by hand and then pressed onto the inner surface of the mold. It is pressed evenly with the pads of the fingers, and then additional clay slabs are sequentially connected and pressed uniformly over the entire surface. At this time, it is important to always keep the balance of the overall wall thickness (mi-atsu) in mind while pressing it tightly against the mold. When making bag-shaped items such as jars or vases, or three-dimensional ornaments, "split molds" (molds that can be divided into multiple pieces) are used. Depending on the complexity of the form, split molds can be simple "two-part molds," "three-part molds," or even more complex multi-part structures.
In modern times, it is much more convenient to use plaster molds, which have excellent water absorption. For thin and small pieces, forming can be easily done by pressing and evening out the thickness with fingertips. However, when making large and thick pieces, the outer surface in contact with the mold rapidly solidifies as the mold quickly absorbs water and moisture, while the inner surface not in contact with the mold remains damp. If a significant unevenness in clay drying speed and hardness occurs in this way, the outer part cannot follow the inner part's shrinkage during the drying process, causing cracks (setsukatsu/kizu) to appear from the inner surface of the vessel. This consideration of drying balance is indispensable, especially when making porcelain (stoneware) with a high shrinkage rate. The burrs (seams) that appear where split molds are joined must be carefully trimmed and smoothed after monitoring the drying progress.
In addition to mold forming using clay molds, there is also a method that combines it with a potter's wheel. When a bowl, plate, or jar is pulled up using an outer mold in conjunction with a wheel, a unique texture is created that is different from hand-pinching or regular wheel throwing. When I was not yet proficient with the potter's wheel, I used a method where I placed the bottom to the waist of the vessel in a clay mold and built up the upper part with coils. This technique can produce a uniquely appealing texture not only for beginners but also when attempted according to the desired form. It is also very interesting to try carving patterns directly into the inner surface of an outer mold to create experimental jars.
【Application Examples of Press Molding】
There is a technique of cutting out a slab (tatara) using a "hego plate" (an extremely thin plate with uniform thickness) or a "hego stick" (a square stick with grooves of different depths carved into its four sides), and then press molding. This is a more advanced method than making slabs by hand. Hego plates require many different thicknesses to be prepared, which is a bit troublesome except for mass production. In contrast, a hego stick with grooves of different dimensions on its four sides is extremely convenient as it allows for cutting slabs of any desired thickness with a single stick. By placing a hego stick or hego plate against a rolled block of clay and sliding a wire cutter (bow cutter) to cut it, a tatara plate of appropriate thickness for the purpose can be obtained. This is very convenient for forming "flatware" such as plates and bowls, and is suitable for press molding using inner or outer molds. When making objects of precise dimensions and shapes, the key point is to ensure that the overall thickness is as uniform as possible when pressing the clay into the mold. If warping or distortion still occurs after drying, using a "double mold" (a mold structure that sandwiches the clay between an outer and an inner mold) yields very good results.
In press molding of porcelain (stoneware), extreme care must be taken at corners and edges, as cracks are prone to occur. Also, when making plates from pottery clay such as Shigaraki clay, using an outer mold tends to cause the bottom to spring up and warp, so using an inner mold is more stable and results in less dimensional distortion. In both inner and outer molds, if a cloth is placed between the clay and the mold and pressed, the clay becomes well-compacted, resulting in a beautiful form.
【Reinforcement and Weight Reduction of Plaster Molds for Large-Scale Production】
When producing large-scale works, plaster molds themselves become considerably heavy, requiring significant effort to handle. Furthermore, to prevent damage to the mold and strengthen it, interweaving cotton (gauze or cloth) within the plaster layers is highly effective. First, a thin layer of plaster is sprinkled onto the master model (original form). Once the surface has slightly hardened, a diluted cotton cloth soaked in thickly dissolved plaster is uniformly laid over the pre-hardened plaster and gently pressed to secure it. Plaster is then applied again over this layer to finish the mold. When creating split molds (multi-part molds) for flatware or hollow items, this reinforcement process is applied to each section of the mold (although small, segmented pieces only require plaster). This allows for a significant reduction in the mold's thickness, greatly lightening its weight, and making handling safer and easier.
【Trial and Practice Using Plaster Molds and Bisque Molds】Forming small and large plates with plaster or clay molds
Prepare an inner mold in the shape of a plate. The slab (tatara) should be of appropriate thickness, but in this case, a slightly thicker and compacted slab will result in a rustic and appealing finish. Place the slab on the plaster mold, cover it with a cloth, and press it evenly by patting it to form the shape. Once removed from the mold, the forming is complete. If the bottom is wobbly and unstable, gently tap it to flatten it. Alternatively, by placing clay of a different color on the slab beforehand and then pressing it with the mold, a type of "inlay pattern" can be created. This can be very effective depending on the choice of glaze. Applying this method to attempt "neriage" (marbled clay) expressions is also good, and the mold can be appropriately selected as an inner or outer mold depending on the work.
【Basics of Neriage Technique and Coloring】
When performing neriage (marbled clay) forming, earthenware clay is the easiest to handle. Prepare two to three different colored clays, but since different types of clay are layered, it is necessary to choose a combination with the smallest possible "difference in shrinkage rate" during drying and firing. As a coloring agent, iron oxide (bengara, etc.) is the most suitable in terms of overall composition and texture. If Shigaraki clay is used as the base, adding about 10% iron oxide will result in a dark brown to black tone, while 2-3% will produce a light brownish-gray. The proportion of light and dark can be adjusted according to the desired effect. It is a rule of thumb to avoid thick glazing on neriage pieces to clearly display the patterns. For example, when creating a striped plate using two types of clay: Shigaraki body and "clay mixed with 10% iron oxide," stack alternating light and dark clay slabs in layers to create a single block. Then, lay it on its side and slice it (cut) to the appropriate thickness with a wire cutter. This will produce a beautifully striped slab. Press this into a mold, and when the clay has firmed up appropriately, remove it from the mold. In this case, using an inverted mold (reverse mold) makes the work easier.
【Uzura-de (Quail-Patterned) Neriage Technique】
This technique is named "Uzura-de" because of its resemblance to the complex, flowing patterns of quail feathers. White and black, or white, black, and gray (light black) clays are alternately stacked to form a block, then cut once, turned sideways, and sliced again to the desired thickness with a wire to create a patterned slab, which is then pressed into a mold for shaping. At this time, care must be taken as the clay at the joints is prone to cracking during drying. In the above, if the layered block is deliberately cut with a dull blade, such as a "bamboo spatula or blunt knife," the clay will be pulled and distorted by the blade, creating beautiful, flowing quail feather patterns (marble patterns). After cutting, lightly tap and compress both sides to ensure the structure is firm. If cut with a tool that cuts smoothly like a wire, the lines will be straight, and the feather pattern will be difficult to achieve. In such cases, peel off each cut slab one by one, moisten your hand with water, and repeatedly smooth and scrape the pattern along the direction of the flow (the feather pattern lines) with your finger to create a very elegant feather pattern expression. Depending on the shape of the vessel being made, it can be effective to deform the clay block itself into the desired form before slicing.
To create "suminagashi" (marble) patterned slabs, lightly knead two to three different colored clays without fully mixing them, then slice and press them into a mold to finish. Additionally, with ingenuity, the range of expression is infinite, including checkerboard patterns and ajiro (basket weave) patterns.
In the works of Aoki Mokubei, a master of Kyoto ware from the late Edo period, one often finds small items such as teapots and sencha cups that were formed using fired "clay molds." This technique is believed to have been strongly influenced by traditional methods like the Yixing teapots of China. The reliefs and patterns on the surface of the vessels were directly carved into the interior of the clay molds. In China, especially during the Song dynasty, many excellent molded pieces were seen, and kōgō (incense boxes) and kōsu (incense containers) are frequently found in works from the Goryeo and Joseon periods of the Korean Peninsula.
There is a technique called "sukashibori mon'yo" (openwork carving) where patterns are drawn on the surface of the vessel and the surrounding areas are cut out. When I once made a brush holder using the coil building method, I tried an expression where the pattern was left in relief and the surrounding space was cut out. It is also entirely conceivable to carve patterns into the mold itself beforehand and apply such openwork carving.
【About Slip Casting】
This is a method of forming by pouring liquid clay (slip) into a water-absorbent plaster mold. It is a technique that has seen remarkable development in recent years and was primarily introduced for the purpose of rationalizing production and mass production. However, this method has a significant advantage: because the slip uniformly compacts due to the mold's water absorption, distortion during firing (firing warpage) is extremely minimal. For thick, non-hollow forms, a "double casting method" (sandwiching the slip between two molds, front and back, and pouring slip into the cavity) is used. At this time, it is important to firmly secure the two molds with string or a vise to prevent them from opening due to pressure. The conical pouring spout attached to the slip inlet can be made from processed galvanized iron or copper plate, about 5-6 sun (approx. 15-18 cm) long. For large or thick pieces, it is best to drop the slip from a high position using a hose, pouring it in with hydraulic pressure. Note that plaster molds for casting should be slightly moistened with water before use to accelerate the absorption rate of the slip.
The slip casting technique has developed remarkably in major pottery production areas in Japan such as Mino and Seto, and there is no better learning experience than observing the actual process. Indeed, pieces fired using slip casting are dimensionally accurate and very impressive. However, they are often too perfectly formed, leaving no room for imperfection. From the perspective of the handcrafted artistic charm, they tend to lack the robust strength of more primitive "pressing" techniques. Nevertheless, incorporating slip casting partially into creative work can sometimes yield unexpectedly positive results. For example, when I once created a large and complex flower-shaped plate (large dish) measuring 39cm x 60cm, after much deliberation between hollowing out (carving) or pressing, I used a double-slip casting method to form it with sufficient overall thickness. At the semi-dry stage, I added a "carving" finish with a carving tool, successfully completing a magnificent piece.
【About Carving (Hollowing Out) Forming】
This technique involves roughly shaping a large block of clay, then, judging the drying state, first carving the outer shape, and subsequently carving out (hollowing out) the inside with carving tools. This process is very time-consuming and laborious, but the finished pieces, carved from a block of clay, possess overwhelming solidity and a strong presence.
【Supplementary Notes and Impressions on Forming】
ⅰ．Skill and Spirit on the Potter's Wheel
In the early stages of pottery making, mastering the potter's wheel requires considerable discipline and training. However, works created at an immature stage of technique can sometimes possess an unexpected, simple charm and beauty. This is similar to being deeply moved by an innocent child's drawing; due to the lack of technical mastery, the maker's honest heart is directly expressed in the work. Of course, the acquisition of advanced skills is indispensable, but above all, a firm mindset of not being controlled by machines or tools is crucial. Working with soft clay on the wheel, confronting the wheel, is like a "sumo wrestling match" with the clay. One must follow the mechanics of the clay, but not be defeated by its momentum and cause it to collapse. The rotational speed during the stretching process is not as critical, but as the shaping progresses, it seems more beneficial to keep the rotation low rather than increasing it too much, as this imbues the work with a warmer spirit. The same applies to finishing processes such as foot trimming.
My procedure for throwing (pulling on the wheel) involves first "rough pulling" to create the general shape, then placing it on a batt to allow the clay to settle a bit, and finally refining the final form while maintaining its softness. This method is particularly effective for making vases and similar items, allowing completion simply by trimming the foot (base) after drying.
ⅱ．Forming Small Plates Using the Slab Roller and a Receiving Ring
First, carve the desired relief pattern into a plaster mold for the interior of the small plate. Prepare a hollow "receiving ring" and place a suitably sized slab on top. Then, press the carved plaster mold from above. The slab will sink into the hollow of the receiving ring, creating a natural depth (rise). Remove the mold, and once the clay has dried sufficiently, remove it from the receiving ring to complete the small plate. The pressing creates natural undulations and distortions in the rim (mouth), which in turn produce a rustic and warm aesthetic. When cutting the slab, leaving the knife marks from using a template further expresses the sensory beauty of handcraft. This technique allows for diverse enjoyment through variations in glazing.
ⅲ．Inlay-style Press Forming Using Different Colored Clays
Either an outer or inner mold is used. Prepare 2-3 different colored clays for the body. Adjust the different colored clay for inlay to be slightly firmer, and press it into the mold. The difference in hardness will create subtle variations in texture and unevenness, which, combined with the flow of the glaze, results in a highly effective design.
Arrange patterns (designs) on the slab using different colored clays as appropriate. Then, apply a plaster mold, invert it, and finish by pressing it with a cloth and fingers, similar to press forming, then turn it back over. At this time, place a clay ring or support underneath to prevent deformation or distortion. For three-dimensional structures such as jars, place the different colored clay for inlay, then press a flat board or similar object onto it to secure it firmly and prevent the pattern from shifting. Keeping the inlay clay slightly firm will create shadows from the unevenness during firing, which, combined with the glaze, will result in a very effective appearance.
【Nerikomi (Mixed Clay) Carving (Hollowing Out) Forming】
The method of mixing clay can be adjusted to your preference. As mentioned earlier, first meticulously shape the outer form, then, once the clay has reached the appropriate hardness, carve out (hollow out) the inside to finish. I tried making a larger box (lidded container) with this technique and achieved an unexpectedly sturdy and compact structure.
【An Idea for Producing Small-Mouth Jars, etc.】
After throwing the body to a sufficient height on the wheel, completely close (seal) the upper mouth and smooth the surface of the vessel. When making flattened jars, for example, if pressure is applied to the sides by hand while sealed, the unpressed areas will naturally swell softly due to internal air pressure. Furthermore, if intentional indentations are created using the pads of the fingers, the internal air has nowhere to escape, causing the areas around the indentations to expand richly, forming a plump and taut three-dimensional shape. However, at this stage, care must be taken to ensure uniform thickness during the throwing process, otherwise, only the thinner parts will swell unnaturally large. Note that for vessels with large openings, the internal sealing effect is diminished, so a significant effect cannot be expected. Once the desired form is achieved, cut the opening with a knife or similar tool to create the mouth.
【Production of Lidded Containers, etc., by Sealed Wheel Forming】
As mentioned, by pulling up a sealed cylinder with the mouth completely closed, and then cutting it at an appropriate point with wire or a needle, a lidded container (盒子) with a precise fitting mouth can be created. If the cut surface is made diagonally (like an inro) or in a wavy curve, the stability of the lid's fit increases, preventing it from falling off. Alternatively, if one throws it on the wheel in the reverse direction (upside down), seals the top, cuts it with a needle, and then attaches a foot (or coils a clay rope and carves the foot) when the clay has reached an appropriate hardness, and then flips it over at the right drying stage, a vessel with a surprisingly sturdy and robust rim will be completed. In this method, it is crucial to carefully consider the remaining finger marks on the inside and how the clay is stretched during the pulling stage. This is because the swelling inside the vessel and the texture of the inner wall treatment significantly influence the final appearance and feel of the work.
【Nerikomi Carving (Making Lidded Boxes and Large Boxes)】
The combination of clays and nerikomi expression are performed as previously described, and the finishing steps are also as already mentioned. Based on my experience creating large lidded boxes, after shaping the outer form, prepare deeply embossed stamp patterns or pre-carved plaster molds, and press a clay slab of comparable size against the mold. At this point, pressing firmly will yield a very powerful three-dimensional relief. While the clay is still soft, cut and separate the top and bottom (body and lid). Then, carve out (hollow out) the inside of both parts, and finally, carve out the fitting mouth as shown in the diagram to join and secure them.
Chapter 7: Electric Kiln Structure and Practical Application of Glaze Firing (Oxidation and Reduction)
【How to Use an Electric Kiln and Drying/Bisque Firing】
Immediately after kiln construction, it is crucial to thoroughly remove moisture from within the kiln. Therefore, conduct bisque firing at approximately 700°C to 750°C several times, or perform an empty firing to completely dry it.
【Precautions During Temperature Increase】
While it varies slightly depending on the size and thickness of the pieces, a slow temperature increase of generally no more than 50°C per hour is safe. The temperature range of approximately 300°C to 500°C requires the most caution. However, for small pieces, there is no need to worry excessively; it is acceptable to maintain full low for about 2 hours before switching to full high. Even for large pieces, it is safe to switch to full high once approximately 700°C is reached.
The temperature range of 300°C to 500°C corresponds to the stage in wood-fired kilns where thick soot (smoke) fills the kiln, and the range of approximately 700°C to 750°C is when the thermal expansion of quartz and other components in the clay body is most vigorous. The peak temperature at which quartz expands to its maximum is said to be around 750°C, so if the temperature exceeds 700°C, the risk of damage from rapid heating is extremely low.
【Operational Procedure for Glaze Firing (My Practice Example)】
The glaze firing procedure currently employed in our studio is as follows:
ⅰ．5 PM - 6 PM: Start with all elements on low.
ⅱ．Around 10 PM - 11 PM: Set the top and bottom elements to "high" and leave them on until early morning.
ⅲ．Early Morning (Upon reaching 700°C - 800°C): Switch all elements to "high." Following this procedure will ensure the firing is complete during daylight hours.
For extremely large or thick pieces, first set the top element to "high" at around 250°C - 200°C, and then set both top and bottom elements to "high" after 1-2 hours. If only one element (top or bottom) is set to "high," it results in a "one high, two low" state. However, please note that when "two high" is set, even if one element is set to low, current will not flow through that low element due to the kiln's structural design.
【Cooling Process】
During the cooling stage, the opposite management from the heating stage is applied. There is no concern about cracking if the temperature drops rapidly until around 700°C, but caution is required once it falls below that temperature range. Nevertheless, with an electric kiln, if the temperature drops to around 600°C, slightly shifting the top lid, and if it reaches 200°C, completely removing the top lid, usually does not cause any problems with the pieces.
【Oxidation Firing (O.F.) Glaze Firing】
The basic firing procedure is as described above. While there are some differences depending on the nature of the work, the target maximum temperature is generally around 1220°C to 1250°C. Around 1230°C corresponds to Seger cone (SK) numbers 9-10. The speed of temperature rise causes some variation in the fired texture.
After reaching the target maximum temperature, turn off the middle element switch, maintain the top and bottom elements on "high" for 30 minutes to 1 hour (soaking), then turn them off. This ensures the heat penetrates thoroughly into the interior of the work, resulting in uniform, well-fired pieces. This is what is known as the "finishing" process. If the middle element is off and only the top and bottom elements are on high, the kiln temperature will not drop significantly. It is advisable to place a Seger cone inside the kiln as a precaution. Placing a Seger cone in a visible position from the peep hole is also a reliable method.
In the case of oxidation firing, if "high" is engaged around 700°C (for large pieces; around 200°C to 250°C for small pieces), it will reach approximately 1000°C in 10-11 hours.
【Reduction Firing (R.F.) Glaze Firing】
The difference from oxidation firing is that wood is intentionally introduced into the kiln from around 900°C to create a smoky atmosphere. The thickness of the wood used can be similar to kindling used in wood-fired kilns. The temperature range for reduction is approximately 900°C to 1170°C. Especially in the 950°C to 1050°C range, it is advisable to create a relatively strong smoky atmosphere. Maintain a vigorous flame of about 15cm (5 sun) blowing out from the peep hole, with smoke billowing out.
Once the temperature exceeds 950°C, it is best to avoid introducing secondary air into the kiln as much as possible, but continue firing while constantly observing the flame at the peep hole (because introducing excessive secondary air can change the color development and reduction state). From around 1170°C, adjust to a light smoke.
When the temperature reaches approximately 1200°C, remove any unburnt wood, close the chimney damper, and seal (block) the kiln to prevent the reducing gases from escaping or diffusing outside as much as possible. This is the best practice. Once the wood in the firebox has completely burned out, seal the firebox and secondary air holes with clay to prevent any cold air from entering. This is done to maintain a uniform temperature throughout the kiln and to allow for slow cooling.
It is desirable to continuously maintain a flame length of 4-5 sun (approx. 12-15 cm) emerging from the peep hole. From 900°C to nearly 1000°C, the amount of secondary air is finely adjusted to control the flame's behavior. The most smoke is generated around 1000°C to 1050°C, so at that stage, secondary air is completely stopped to suppress excessive smoke emission. Above 1050°C, it is sufficient to introduce 2-3 pieces of wood at a time, just enough to keep the fire going. Note that if the firing is overly smoked after the glaze surface begins to develop a sheen, it can adversely affect the color development of glazes like white glaze, making them appear dirty.
For a 15K (kilowatt) capacity electric kiln, approximately 1.5 Kyoto bundles of wood are sufficient for one reduction firing. The purpose of introducing wood is to generate carbon monoxide (CO) to create a reducing atmosphere (R.F.), and better results are achieved by controlling the wood so that it does not burn out too fiercely and quickly.
【Gas Generation from Glaze and Heater Element Management】
Glass, barium, and titanium glazes tend to generate bubbles (gas) from within during firing. In such cases, if the top lid is slightly opened up to around 1000°C to allow gases released from the glaze to diffuse and escape from the kiln, and then the lid is completely closed after exceeding 1000°C, good results can be obtained.
For the maintenance of heating elements, extreme care must be taken to prevent glaze or salts from adhering to them. Once used for firing, heating elements become very brittle and prone to breaking, so they must not be scratched or forcibly bent. In the event that a retaining pin comes loose or falls out, it is important to carefully insert and secure a spare pin.
Chapter 8: Kiln Packing and Kiln Furniture/Shelving Maintenance
【Safe Operation of Power Switches and Kiln Packing】
When loading the kiln, the absolute priority is to ensure that the main switch on the main distribution panel is turned off. If you work with the switch on and accidentally touch a heating element, there is an extremely dangerous risk of electric shock. Similarly, after firing is complete, it is essential for safety to make a habit of always turning off the main switch.
When starting the kiln, always turn on the main switch on the distribution panel first, and then turn on the switch on the electric kiln itself, in that order.
The heating elements inside the kiln are divided into three systems: "upper," "middle," and "lower." When set to "high," current flows even if only a single system, such as the upper or lower, is engaged. However, when set to "low," current will not flow if only one of the upper, middle, or lower systems is engaged. The circuit design requires at least two systems to be engaged simultaneously for current to flow.
【Kiln Furniture Materials and Blending】
Kibushi clay (also known as Dosenbo clay), which has high refractoriness and excellent plasticity (stickiness), is extremely suitable for making kiln furniture.
Carborundum (silicon carbide) shelves and posts (props) are excellent, and they are very convenient when stacking them to adjust height according to the workpieces or shelf arrangement.
While various sizes of commercially available carborundum posts exist, slight dimensional inaccuracies can lead to inefficiencies. In such cases, it is advisable to make your own clay posts. The clay for this purpose should be made by thoroughly kneading a mixture of "Kibushi clay 5 : Shigaraki clay 5."
【How to Make Posts and Kneading Method】
To knead the clay, thin slices of both kibushi clay and Shigaraki clay are cut, stacked alternately in multiple layers, and then kneaded together to achieve a uniform clay body.
When making posts, the clay is rolled into rods, cut to appropriate dimensions, and then shaped by tapping both ends on a flat board. It is crucial to make each post precisely the same height; otherwise, the shelves will wobble and become unstable when stacked.
【Preventing Sticking with Alumina and Using Tochin】
To prevent shelves and the bottom (foot) of pieces from sticking together during stacking, it is convenient to use aluminum oxide (alumina powder). Quartz powder can also be used, but since quartz tends to react with basic components in the clay body and glaze, melting and adhering, it is much safer to use highly refractory alumina.
When using it, simply wrap alumina powder in a cotton cloth or similar material and lightly sprinkle it on the bottom of the piece and the shelf. A thin scattering of powder is sufficient.
However, when firing pieces with glazes that tend to run (drip) significantly, place a "tochin" (sacrificial base) made of kibushi clay, cut to the same size as the piece's foot, underneath. Apply a mixture of "alumina powder mixed with funori (seaweed glue)" between the piece and the tochin to adhere and fix them. In this case, the alumina layer should be relatively thicker than usual.
【Repairing Shelves and Surface Dressing】
If glaze runs and adheres to the shelf surface, or if the shelf is otherwise scratched or damaged, use a small "chisel" (available at building material stores) and tap it with a hammer to cleanly remove the adhering material (always use a chisel; hitting the shelf directly with a hammer could crack the board).
After removing it, carefully apply "dressing clay (repair material)" to the surface, allow it to dry thoroughly, and then grind the surface with a coarse whetstone (carborundum whetstone) to restore it to its original flat state.
While it is most reliable to purchase repair materials from the shelf manufacturer, if you are making your own substitute, a mixture of "kibushi clay (120-mesh powder) 30 : alumina powder 30 : Mitsuishi powder 30" with funori liquid added and mixed, then applied, works well.
Chapter 9: Frit Production and Calculation of Soft Glaze (Low-Fire Glaze) Formulas
【Frit Production Using the Main Kiln】
Prepare a concentrated mixture of the desired raw materials, place it in a prepared refractory container (sagger, etc.), and melt it together with the pieces during the main kiln firing. Frit melts sufficiently around 1150°C, so there's no need for special temperature settings; it can be fired at the same temperature as the pieces. However, the absolute condition for making frit in the main kiln is to do so under "oxidation firing (O.F.)."
Place the frit raw materials in a sagger and load them into the kiln. If the sagger should crack and the frit leak out, it could contaminate the kiln interior and other pieces, causing immense damage, so utmost care must be taken to ensure it does not break. Melted frit glaze becomes a thin, syrup-like liquid, making strict caution even more necessary.
The inside of the sagger should be thickly coated beforehand with "quartz powder dissolved in funori (seaweed glue)." After firing and removal from the kiln, break the sagger and carefully grind away any quartz adhering to the frit surface with a grinder or similar tool. Then, reheat the frit until it reaches a dark red color (approx. 600°C-700°C) and quickly plunge it into cold water, causing it to shatter into small pieces due to thermal shock. Transfer this to a ball mill and pulverize it into a fine powder. Coating the inside of the sagger with quartz makes it easier to remove the solidified frit from the container. As a container, it is safer to use a proper graphite crucible instead of a sagger, as there is no risk of breakage.
When using a dedicated frit kiln, there are methods such as allowing the melted frit to flow out from a bottom hole and drop into water below to shatter, or ladling it out from a crucible in the kiln and dropping it into water. Since it is desirable for unwanted gases within the frit to diffuse and escape as much as possible for higher quality frit, the latter ladling method is superior.
While producing frit in a dedicated frit kiln is more efficient for mass production, creating frit by slow firing in the main kiln is surprisingly simpler for individual artists and is very convenient for obtaining high-quality low-fire glazes. However, for large quantities, the dismantling and pulverizing process is the most labor-intensive drawback.
【Basics and Principles of Soft Glaze (Low-Fire Glaze)】
The melting point of soft glazes (low-fire glazes) is generally around 700°C to 800°C, but some melt around 1000°C, and a few even around 1150°C to 1160°C.
They are primarily made by combining silica with strong fluxes such as lead, soda, borax, potash, barium, and limestone.
The chemical properties of representative raw materials I have used in experiments over the years are as follows:
・BaCO3 (Barium Carbonate): White powder, insoluble in water
・CaCO3 (Limestone): White powder, insoluble in water
・PbO (Lead Oxide): Yellowish powder, insoluble in water
・PbCO3 (Lead Carbonate): White powder, insoluble in water
・Na2CO3 (Anhydrous Sodium Carbonate): White powder, soluble in water
・Na2B4O7+10H2O (Borax): White, slightly crystalline powder, soluble in water
・K2CO3 (Potassium Carbonate): White powder, soluble in water
When using water-soluble raw materials (such as sodium carbonate, borax, potassium carbonate) in glazes, if applied directly, they will dissolve in water and be absorbed by the clay body. Therefore, they must first be heated and melted to vitrify (frit) them.
Especially borax, when heated over a flame using a pan (horaku) or similar, its crystal water evaporates, causing significant expansion (bloating). Therefore, it is much more practical to use "calcined borax (anhydrous borax)," which has been fired and solidified, rather than using the raw material directly.
【Example Calculation for Calcined Borax Formulation】
The molecular weight (formulation amount) of raw borax (Na2B4O7 + 10H2O) is 191.7, and the molecular weight of calcined borax (Na2B4O7) after losing its crystal water is 101.3.
If a formulation specifies using 50% raw borax, the calculation to substitute it with calcined borax is as follows:
Therefore, to achieve an equivalent chemical composition, approximately 26.38% calcined borax should be blended instead of 50% raw borax.
For mass production, using a frit kiln is efficient, but for individual artists, making frit by oxidation firing in the main kiln is surprisingly simpler and very convenient for obtaining high-quality low-fire glazes.
Chapter 10: Overglaze Pigments (Japanese and Western Pigments) and Gold/Silver Decoration Techniques
【Characteristics of Overglaze Pigments (Japanese and Western Pigments)】
Overglaze pigments are broadly classified into two types: "Japanese pigments" and "Western pigments."
The former, Japanese pigments, exhibit high "transparency" like glass after firing, while the latter, Western pigments, generally show "opacity" as their fundamental characteristic and common understanding.
Western pigments are commercially available at pottery supply stores and come in a wide variety of colors. It is also a good method to mix an appropriate amount of Western pigment into the base glass glaze (frit) when making Japanese pigments yourself. However, with Western pigments, depending on the type of chemical composition, thinning them for use can sometimes result in unexpected colors completely different from what was imagined.
For example, "black" Western pigment is a powder composed of iron, cobalt, chromium, etc., which has been fired and crushed together with a glass solvent. Therefore, if it is thinned with water or oil and applied, the strong blue color of cobalt may become prominent, resulting in a bluish-black.
Traditionally, Japanese pigments that originated in China primarily consist of basic colors such as "red, green, yellow, purple, black (and indigo)."
During the Qing Dynasty, extremely delicate and beautiful pigments such as "fencai (famille rose)" were used, which are believed to have been prepared by blending components of Western pigments with glass flux. As a result, their transparency has a slightly opaque texture compared to traditional Japanese pigments.
I personally prefer the transparent and deep texture of traditional Japanese pigments and have used them for many years.
【Selection and Technique of Overglaze Red Pigment】
Various types of red pigments (aka-e-gu) are sold at ceramic pigment stores, so it is best to select them as appropriate for your artistic style.
The old Kutani-style red that I favor shows a relatively subdued and sophisticated color, and it is primarily well-suited for porcelain (stoneware) bodies. On the other hand, when applied to earthenware (clayware), it is often better to use a slightly more vibrant and vivid commercially available overglaze red to achieve a balanced color.
First, apply red entirely to the body (red ground), and once it dries, paint patterns with green, yellow, or other Japanese pigments. This results in a work with a very tasteful and deep tone.
【Kinrande (Gold Brocade) Technique】
The "Kinrande" technique, which applies gold on a red ground, is performed in a similar manner to the above.
First, apply red pigment thoroughly, fire it in the overglaze kiln once to fix it (overnight firing), and then apply delicate gold leaf (gold powder) painting on the red ground. Finally, fire it again to finish.
【Mixing Ratios for Gold and Silver Inks and Polishing Finish】
The appropriate mixing ratios for gold and silver decoration are as follows:
・Gold (Gold powder, dead gold) Mixture
Mix gold powder (dead gold, which is gold leaf ground into fine powder) at a ratio of 10 parts to 1 part of Japanese pigment (yellow type) or Western yellow (Western pigment yellow).
・Silver (Silver powder) Mixture
Mix silver powder at a ratio of 10 parts to 0.5 parts of Japanese pigment (colorless transparent type) or white enamel pigment.
Both gold and silver inks appear matte immediately after firing in the overglaze kiln. After firing, carefully polish (burnish) the surface using a glass brush, ultra-fine sandpaper (waterproof abrasive paper), or an agate burnisher. This process reveals a dazzling metallic luster.
Chapter 11: Secret Formulations of Japanese Pigments, Substrate Compatibility, and Special Decorative Techniques
【Red Color (Single Use) Formulation and Application Technique】
・Normal: Isekyu No. 1 Kutani Red 100 / Komei-in Benibana 5 / Antimony Oxide 3
・Strong (Subdued): Isekyu No. 1 Kutani Red 100 / Komei-in Benibana 10 / Antimony Oxide 10
・Slightly Yellowish (Yellow-toned, Bright): Isekyu No. 1 Kutani Red 100 / Antimony Oxide 3
The finer the red pigment is ground, the more beautiful the red color becomes. This is an absolute requirement for red overglaze painting.
When dissolving red pigment, it is effective to use good quality green tea (koicha). The components in the tea create an appropriate stickiness, making it very easy to handle. Mixing animal glue, as is done when dissolving Japanese painting pigments, is also effective, but care must be taken not to use too much. While mixing glue allows for uniform application over large areas without unevenness, it tends to make the paint run off slightly during firing.
In the "tatara-tataki" technique, red pigment is thoroughly ground with balsam oil (terpene oil type). Using tools like a glass plate or a porcelain mortar and pestle is extremely convenient for preparing overglaze pigments. Cotton wool is wrapped in a very fine cotton cloth, soaked with pigment, and then dabbed onto the surface of the work. By carefully repeating this, an extremely smooth and even surface coating can be achieved.
In all overglaze firings, moisture in the clay body and pigments must be completely removed. An overglaze kiln (nishiki-gama) that has not been used for some time should be preheated (roasted) before loading to remove internal moisture. Overglaze kilns are fired in "oxidation firing." The typical firing temperature range for nishiki-gama is around 700°C to 750°C, and for the formulations described in this document, 730°C is considered the appropriate and standard temperature.
【Motivation for Basic Formulation of Green Glaze for Japanese Pigments】
The motivation for establishing the basic formulation of green glaze for Japanese pigments as "Tang clay 77 : Quartz 23" came from the observation that the yellow glaze in Tang Dynasty "Tang Sancai" was created by combining red clay (iron-containing clay) and a lead-based flux. Tang clay (a white clay formulation primarily containing lead compounds) possesses relatively broad flexibility (tolerance) to thermal expansion and contraction. Focusing on this characteristic, and after repeated test firings by incrementally varying the mixing ratio of Tang clay and quartz, an exquisite match was found at 77:23.
Furthermore, if a frit (vitrified material) is made beforehand using the above formulation and an appropriate amount is mixed into the raw glaze, it results in smoother melting, among other effects (though not strictly essential). When applying glaze to bisque-fired ware, the mixing ratio can be appropriately strengthened.
It is possible to substitute Amakusa pottery stone or feldspars for quartz, but since feldspars do not contain crystal water, substituting them might be preferable for ease of handling. As for the source of lead oxide, lead tetroxide (red), lead oxide (yellowish), or Tang clay (white) can all be used, but from the perspective of compositional specific gravity balance, "Tang clay" is the easiest to handle and most suitable.
【Mixing Ratio of Green Japanese Pigment and Prevention of Peeling】
・Dark Green: Tang Clay 77 / Quartz 23 / Copper Oxide 4
・Normal: Tang Clay 77 / Quartz 23 / Copper Oxide 3
・Frequently Used by the Author: Tang Clay 77 / Quartz 23 / Copper Oxide 3.5
Copper oxide (CuO) used as a colorant may be substituted with copper carbonate (CuCO3). When replacing copper oxide with copper carbonate, convert at a blending ratio of 6% CuCO3 for every 4% CuO.
When Japanese pigments are thickly applied over a wide area on already fired and glazed non-crazing porcelain bodies, the pigment film tends to peel off (exfoliate) during cooling. I myself struggled greatly with this peeling phenomenon for many years.
Investigating old records of general Japanese pigments often reveals the inclusion of "leaded white jade (lead frit)." However, analysis and experimentation with commercially available white jade frit showed that, despite being labeled "leaded," it actually contained soda (Na) and potash (K) components. These alkaline components have extremely high thermal expansion coefficients, and thus cannot withstand the difference in thermal expansion with non-crazing porcelain bodies, which have low expansion/contraction. This causes peeling during the cooling process after firing, due to the pulling force from the difference in contraction with the body.
Therefore, I chose "pure lead" as the sole flux, given its excellent resistance to expansion and contraction (tolerance).
Incidentally, if the ceramic body has crazing (fine cracks), the melted Japanese pigment will firmly penetrate and anchor within the cracks, preventing peeling. Therefore, when applied to ceramics, excessive caution is unnecessary, and it can be safely fired even if white jade frit is mixed in as with normal Japanese pigments.
【Consideration of Old Kutani Japanese Pigments and Body Characteristics】
Observing masterpieces of old Kutani ware, it is evident that even with thick applications of green and purple Japanese pigments over large areas, no peeling occurs. The body of old Kutani ware is a dense clay that is too compact for glaze crazing, and it has stronger refractoriness than Kyoto ware, being fired very hard at high temperatures. The texture and color of this body are close to earthenware.
It is believed that due to these body characteristics, the thermal expansion and contraction rates of the green and purple overglaze pigments and the body itself are extremely close, preventing peeling. Furthermore, it is presumed that the overglaze firing temperature for old Kutani ware was slightly higher than usual, around 750°C to 760°C, a strong fire.
Moreover, it appears that the silica used in the formulations was not pure silica but raw clay containing appropriate feldspar components (alumina), which was then mixed with lead. It is also acceptable to use Amakusa pottery stone or feldspar instead of silica, and the appropriate addition of alumina creates a calm, moist, deep luster in the color development of the overglaze pigments.
The black pigment used for bone drawing (black outlines) in old Kutani ware is likely "Noto GOSU" (manganese-containing ore) from the local area.
Note that red pigments (pink/red series) that develop color in the main kiln are made by adding "gold powder" instead of red iron oxide, mixing it with alumina, etc., and refiring it at a high temperature (fritting it).
【Various Formulations and Uses of Japanese Pigments】
Except for red and black, all transparent Japanese pigments are ground very finely with water in a mortar (wet grinding), then dried once, and then used by adding funori liquid and carefully grinding again. The basic application method is to paint thickly like mud paint.
・Formulation of Yellow Japanese Pigment
ⅰ．(With Western Yellow Pigment, Author Recommended): Tang Clay 77 / Quartz 23 / Western Yellow Pigment 10
ⅱ．(With Traditional Benibana): Tang Clay 77 / Quartz 23 / Komei-in Benibana 2-3
Formulation ①, which incorporates Western yellow pigment, is very simple, so I primarily use it. Adding commercially available overglaze red (or Western yellow) is easier to handle than incorporating Benibana, and a beautiful yellow can be obtained with less than 10% inclusion. In ancient Chinese ceramics, old Kutani, Kakiemon, and other traditional works, it seems that most used Benibana (trace amounts of bengala) as an opacifier and colorant. I have also tried yellow with Benibana formulation, but since there are no precise records, I conduct a color test (test firing) before use.
・Formulation of Purple Japanese Pigment
ⅰ．Mixing Ratio: Tang Clay 77 / Quartz 23 / Main Kiln True Engineer 0.5 / Manganese Oxide 1.0
(Purple has a stronger color development than yellow or green, so the amount of manganese added should be carefully adjusted to a minimum.)
Records indicate that "Tang GOSU" was historically used as a purple colorant, and I have used it myself. However, Tang GOSU has the disadvantage of having a high melting point and being difficult to melt. Therefore, manganese oxide is used. The material referred to as "Junto GOSU" is also manganese-based. If the color development with the above formulation is too vivid, it is advisable to formulate it by keeping the amount of manganese as small as possible.
・Formulation of Indigo (Ultramarine) Japanese Pigment
ⅰ．Mixing Ratio: Tang Clay 77 / Quartz 23 / Western Pigment Ultramarine 5
For convenience, "Western pigment ultramarine" is used as a colorant, but the essential coloring agent is cobalt. Cobalt fired for the main kiln or cobalt nitrate (dissolved in hot water, precipitated with ammonia water, and then dried) can also be used. However, cobalt compounds are extremely potent in color development, so it is necessary to perform color tests (test firings) incrementally starting from a trace amount of about 1%.
・Formulation of Black (for Bone Drawing) Japanese Pigment
Historically, manganese-containing natural mineral raw materials called "Tang GOSU" and "Noto GOSU" have been used. It is believed that this color was also used for bone drawing (outline lines) in old Kutani ware. When layering transparent Japanese pigments (such as green or purple) underneath or over, it is sufficient to paint with GOSU alone (single ingredient). If only black lines are to be exposed without overglaze, a flux (glassy material) is mixed in to prevent flaking. For simple black line drawing, using commercially available "Western black pigment" is the easiest method.
・Replacing silica in basic glaze compositions
The silica in basic glaze compositions can be replaced with Amakusa pottery stone or feldspars with extremely good results. It is recommended to adjust the ratio as needed, using "Amakusa stone 80: Karatsu clay 20" or "Feldspar 80: Karatsu clay 20" as a standard. By mixing feldspar or pottery stone, alumina (aluminum oxide) is added, bringing the chemical composition of the overglaze closer to that of the porcelain body, which enhances adhesion and depth of color. In Kyoto, a raw clay called "Hinooka silica" was once favored. This silica, being low in purity and containing an appropriate amount of clay, proved to be very effective in the fusion and adhesion of overglazes.
【Artificial iridescence technique and the application of Turkish blue glaze and Cizhou ware-style underglaze pigments】
During the war, I once half-buried a broken pot in the garden soil and placed small porcelain pieces with overglaze inside, leaving them for about 10 years. When I retrieved them years later, I found that the green sections of the Japanese pigments on the pieces submerged in the muddy water at the bottom had completely undergone "iridescence," and could no longer be easily rubbed off. This was a valuable experience that demonstrated that the iridescence phenomenon occurs not only with soda ($\text{Na}$) components in ancient glass, but also with lead-based glazes (Japanese pigments).
I invented a method to artificially induce this fantastical iridescence phenomenon, seen in ancient artifacts, overnight. By moistening sand with a tin chloride (SnCl2) solution, burying the artwork in the damp sand, and leaving it to sit while maintaining a temperature of around 100°C (like warm water), a beautiful iridescent film forms on the surface of Turkish blue glaze or Raku glaze in just one night. This reaction is particularly strong with green and blue glazes that use copper ($\text{Cu}$) as a coloring agent, resulting in a dignified iridescent texture reminiscent of excavated ancient artifacts.
Iridescence treatment composition and conditions: Dissolve 5g of tin chloride in 100 parts water, wet the sand with this solution, maintain the sand's temperature at approximately 100°C, and leave overnight.
In regions such as Persia and the Middle East, abundant natural soda (alkali) resources have been available since ancient times, leading to the creation of numerous ancient glass and splendid turquoise-green ceramics known as "Turkish blue." In low-fired soft glazes, when copper (Cu) is used as a colorant, using "lead" as a solvent results in a vivid green (Oribe style), while using "soda (alkali)" produces a beautiful, brilliant blue (Turkish blue). This is an unshakeable chemical truth in practice.
Observing ancient artifacts excavated from places like Egypt, their clay bodies contain little iron and a lot of silica sand, fired at extremely low temperatures, making them brittle. When buried in soil for many years, the glaze surface becomes iridescent, emitting a mystical, iridescent luster. Due to the dry climate of the Middle East, they retain their shape, but in humid environments like Japan, weathering and disintegration are more likely to occur. I once experienced a case where, when repairing a broken part of a Tang Sancai funerary figure (dogu) with plaster, the clay dissolved and disintegrated simply from water permeating the body.
Furthermore, works using lead-free white frit (soda-based alkali frit) may exhibit a phenomenon where white powder (free soda content) erupts on the glaze surface (mold or crystallization) during high humidity, such as in the rainy season, due to residual soluble components in the frit. However, if this is patiently wiped off with a cloth each time it occurs, the eruption will eventually subside, and the glaze surface will settle into its original moist, deep luster. Even with homemade frit, a similar phenomenon is observed if gas escape during melting is insufficient.
・Ekōrai Black (Cizhou ware-style iron black underglaze pigment) Composition
ⅰ. Composition Ratio: Manganese Oxide 15 / Iron Oxide 30 / Amakusa Pottery Stone 40 / Wood Ash 15
The above is the most suitable black underglaze pigment for the powerful black painted patterns seen in Song Dynasty Cizhou ware and Ekōrai, or for black linear drawing as an underglaze for Turkish blue glaze. For the iron oxide (colcothar) to be blended, use high-quality material with a purity of 75% or more. If using raw material of lower purity, adjust by increasing the amount added. This underglaze pigment exhibits an excellent tone when painted directly on raw clay bodies or raw glazes in high-fired kilns (high-temperature firing). When using, mix and grind with funori liquid.
・Kawai Kanjiro's Secret Turkish Blue Glaze Composition
i. Lead-free white frit (soda frit): 100
ii. Tin oxide (SnO: opacifier): 1.5
iii. Copper carbonate (CuCO: colorant): 4.2 to 2.6 (4 to 5% depending on adjustment)
Chapter 12: Glaze Compositions and Compound Glazing Techniques Announced by the Late Kanjiro Kawai
【From My Records (Regarding the Presentation Records of the Late Kanjiro Kawai)】
These are research experience records of "Glaze Compositions and Their Combination Techniques" presented by the late Kanjiro Kawai to a gathering of Kyoto potters on February 1, 1943 (Showa 18), in the midst of World War II. This is an extremely valuable document, and I (Mitsuo Kano) later re-tested all the listed compositions, which proved to be very useful in my pottery making. Some of the low-temperature glaze compositions I use are based on this presentation, and I believe that Mr. Kawai's formulas for reproducing the glaze tones of Tang Sancai remain the best in Japan even today.
Note that the high-fired glazes described here are primarily intended for oxidation firing.
These records were presented by Mr. Kawai himself, who drew tables and displayed them. However, it seems I was the only potter present who immediately copied all the data. Now, as I reflect on the recent major retrospective exhibition of the late master at Takashimaya, I am keenly aware of the great value of these personal experience records.
(Recorded May 26, 1967)
【Kanjiro Kawai Glaze Combinations and Compositions (Presented at Konkoin on February 1, 1943)】
*Primarily for oxidation firing
(1) Iron Red Glaze: Limestone glaze 750 / Ferric Oxide (Fe2O3) 100 / Silica 150
(2) Iron Red Glaze: Serizawa Stone (Mashiko Red Powder) alone, or Kimachi Stone alone
(3) Iron Red Glaze for Daigake (Splatter Glazing): Serizawa Stone bisque powder 90 / Ferric Oxide (Fe2O3) 10
(4) Iron Red Glaze for Daigake (Splatter Glazing): Inayama Red Clay (or Ocher) slip 10 cups / Wood Ash Glaze slip 3-4 cups
(5) Iron Black Glaze (Persimmon Black Glaze): Serizawa Stone 80 / Wood Ash 20
(6) Iron Black Glaze: Serizawa Stone 80 / Wood Ash 20 / Straw Ash 10
(7) Iron Black Glaze (Suitable for layering and combination glazing): Limestone glaze 75 / Ferric Oxide 8 / Chromium Oxide 1 / Cobalt Oxide 0.5 / Silica 14
(8) Iron Yellow Glaze: Serizawa Stone 40-30 / Wood Ash 60-70
(9) Iron Yellow Glaze: Feldspar 10 / Wood Ash 10 / Ocher 10
(10) Blue Glaze: Wood Ash Glaze 100 / Copper Oxide (CuO) 4
(11) Blue Glaze for Daigake (Splatter Glazing): Wood Ash Glaze 100 / Copper Oxide 9
(12) Silk Glaze (Fired to maturity at Seger Cone SK6):
(A) Wood Ash Glaze 80 / Lead-free white frit 20 / Copper Carbonate (CuCO3) 3
(B) Wood Ash Glaze 80 / Lead-free white frit 20 / Copper Carbonate (CuCO3) 9
(13) Opaque Gloss White Glaze: Feldspar 30 / Wood Ash 25 / Straw Ash 45 / Limestone 10
(*Standard basic ratio for opaque glaze: Feldspar 10 / Wood Ash 10 / Straw Ash 10)
(14) Opaque White Glaze Combination:
(A) Feldspar 20 / Wood Ash 20 / Straw Ash 60 (Good for SK10 Reduction Firing R.F)
(B) Feldspar 30 / Wood Ash 30 / Straw Ash 40 (Suitable for SK12 Oxidation Firing O.F)
(15) White Engobe:
(A) Pyrophyllite 60 / Feldspar 40
(B) Pyrophyllite 25 / Feldspar 50 / Gaerome Clay 25 (Composition (B) is very good)
(16) White Engobe: Shigaraki Clay alone (Shigaraki Clay can be mixed with 50% of the white engobe from (15), and a small amount of salt can be added for thick application)
(17) White Clay Body for Inlay: Porcelain body 100 / Shigaraki Clay 20 / Silica 2
(18) Black Engobe (for Itchin/Slip-trailing): Shigaraki Clay 100 / Ferric Oxide 8 (*Use Shigaraki Clay in a ratio of 50% fired clay and 50% water-washed raw clay)
(19) Low-Fired White Glaze:
(A)-(B) Lead Carbonate (PbCO3) 85-70 / Feldspar 15-30
(20) Low-Fired White Glaze: Lead Carbonate 50 / Feldspar 50 / Ashinuma Stone 10 (Ashinuma Stone can be substituted with Kimachi Stone or Kamogawa Stone)
(21) Low-Fired Yellow Glaze:
(A) Lead Carbonate 85 / Ocher (or Red Clay) 15
(B) Lead Carbonate 70 / Ocher (or Red Clay) 30
(C) Lead Carbonate 65 / Ocher (or Red Clay) 35
(22) Low-Fired Pale Yellow Glaze: Lead Carbonate 70 / Feldspar 15 / Ashinuma Stone 15
(23) Low-Fired Dark Yellow Glaze: Lead Carbonate 70 / Ashinuma Stone 30
(24) Low-Fired Light Brown (Kaba-iro) Glaze: Lead Carbonate 85 / Ocher 20 / Copper Carbonate 2
(25) Blue-Green (Aona) Glaze for Daigake (Splatter Glazing): Lead Carbonate 70 / Silica (SiO2) 30 / Copper Carbonate 4
(26) Blue Glaze for Color Shrinkage: Lead Carbonate 64 / White Frit 24 / Silica 12 / Copper Carbonate 3
(27) Green Glaze for Color Shrinkage: Lead-free White Frit 100 / Copper Carbonate 3 / Ocher (or Red Clay) 10 / Tin Oxide (SnO2) or Silica 15
(28) Low-Fired Matte Glaze:
(A) Lead Carbonate 50 / Feldspar 32 / Barium Carbonate (BaCO3) 12 / Pyrophyllite 5 / Silica 1
(B) Lead Carbonate 50 / Feldspar 32 / Barium Carbonate 12 / Pyrophyllite 5 / Copper Carbonate 4 / Silica 1
【Kanjiro Kawai's Glaze Combination Techniques (Category 1 and Applied Developments)】
(*Combination application techniques for the aforementioned composition formulas: (1) Iron Red, (2) Iron Red, (5) Iron Black, (6) Iron Black, (7) Iron Black)
① Single glaze application
② Partial decoration such as pour glazing
③ Apply wood ash glaze as an underglaze, then pour glazes from ① and ② over it (for large works)
④ Apply wood ash glaze as an underglaze, apply wax resist patterns, then pour glazes from ①, ②, ⑤, ⑥, ⑦ over it (optimal for Seger Cone SK9 reduction firing R.F)
⑤ Sgraffito (apply a thin layer of glazes ①, ②, ⑤, ⑥, ⑦ while the clay body is leather-hard, then carve out patterns with a bamboo spatula or similar tool)
⑥ Finger sgraffito (wipe away the glaze with fingertips immediately after application to create patterns)
⑦ Apply wood ash glaze as an underglaze, then immediately after layering glazes ①, ②, ⑤, ⑥, ⑦, use a finger to wipe away the top glaze
⑧ Draw wax resist patterns with glaze ① or ②, bisque fire once, then apply wood ash glaze comprehensively over it
⑨ Apply a thin underglaze of ① or ② with wax resist patterns, then layer black glazes from ⑤, ⑥, ⑦ (or vice versa)
⑩ Apply glazes ①, ②, ⑤, ⑥, ⑦ with wax resist patterns, then layer (14) Opaque White Glaze (A) or (B) over it (can also vary by pour glazing glaze ① on the top and bottom)
⑪ Apply glazes ①, ②, ⑤, ⑥, ⑦ over Itchin (slip-trailing) decoration made with clay of the same quality as the body (slip for clay body)
⑫ Combine and apply glazes ①, ②, ⑤, ⑥, ⑦ over (10) Blue Glaze using the methods described above
⑬ Experiment with layering and combining glazes ①, ②, ⑤, ⑥, ⑦ over (13) Opaque Gloss White Glaze
⑭ Apply Itchin (pipette slip-trailing) patterns in all glazing processes
⑮ Apply red glaze ① or ② as an underglaze, then try method ⑥ or ⑦ over it
⑯ Layer red glazes ①, ②, ③ over black glaze ⑥ or ⑦ as an underglaze
⑰ Splatter glaze (Daigake) (3) Iron Red Glaze for Daigake over black glazes ⑤, ⑦ (Oxidation firing O.F to about SK9. Suitable for the fire-holding section before the second fire in climbing kilns. Also applicable to Itchin, pour glazing, and wax resist)
⑱ Apply red glaze ③ (3) or (4) as a slightly thin underglaze, then use black glazes ⑤, ⑦ in the same way as ⑰
⑲ Apply (4) Iron Red Glaze for Daigake raw on a soft unfired clay body, and apply line drawing, finger drawing, and sgraffito decoration
⑳ Apply (4) Iron Red Glaze to a raw clay body, and apply pour drawing or Itchin slip-trailing with Shigaraki slip from a pipette
㉑ Apply (3) Iron Red Slip for Daigake, create wax resist patterns, bisque fire, then layer wood ash glaze over it
㉒ Perform the reverse process of ㉑ (wood ash glaze + wax resist + red slip + bisque fire)
Chapter 13: Kaori-sensei's Turkish Blue Frit Composition
① Kaori-style Turkish Blue Frit Basic Composition (Ratio)
Limestone 6.0 / Borax crystals 12.0 / Anhydrous sodium carbonate (soda ash) 5.0 / Potassium nitrate (saltpeter) 3.0 / Zinc oxide (zinc white) 4.0 / Silica 12.0 / Tin oxide 0.3 / Copper carbonate 1.3 (Total 43.6)
(*The above raw materials are melted and vitrified to form the frit)
② Simple Formula: Lead-free white frit 100 / Copper carbonate (CuCO3) 4-4.5
③ Author's (Mitsuo Kano) Practical Formula (Firing Temperature approx. 750°C)
Lead-free white frit 80 / Karatsu clay 15.4 / Silica 4.6 / Copper carbonate 4 (Total 104)
1-2% of tin oxide (SnO2) may be added to the above composition ③. Tin oxide has the effect of imparting moderate opacity (a soft, milky white appearance) to the glaze.
A small amount of lead is added to this composition to prevent blistering and defects during firing and to improve the yield (success rate). This small amount will not detract from the beautiful, vivid blue color characteristic of Turkish blue.
Lead-free white frit tends to settle very easily in water, so when glazing, it is convenient to mix it with funori liquid to maintain its suspension. When applying with a brush, if you apply multiple layers (2-3 times) while allowing each coat to dry, you will achieve a smooth, uniform thickness without streaks.
When using this Turkish blue glaze, it is generally recommended to apply it after the clay body has been well-bisqued at a high temperature (strong bisque firing) (however, it is believed that ancient Persian and similar excavated originals were raw-glazed).
Chapter 14: Ceramic Techniques and Decoration Methods Classification List (All 27 Types)
1. Engobe (Keshō): A technique of applying slip to the surface of the clay body to prepare the base.
2. Brushwork (Hakebiki): A technique of dynamically applying slip or pigments with a brush.
3. Comb Carving (Kushigaki): A technique of carving linear patterns on the surface of the clay body or slip with a comb-like tool.
4. Brush Painting (Fudegaki): A technique of directly drawing lines or patterns with a brush.
5. Finger Sgraffito (Yubigaki): A technique of creating patterns by scraping off glaze or slip with fingertips.
6. Sgraffito (Kakitori): A technique of scraping off clay or glaze from the surface with a spatula or similar tool to expose the underlying layer.
7. Nail Carving (Kugibori): A technique of incising sharp lines into the clay body with a sharp metal tool like a nail.
8. Inlay (Zōgan): A technique of embedding different colored clay or pigment into carved grooves.
9. Wax Resist (Nukirō): A technique of drawing with melted wax to repel and prevent glaze from adhering.
10. Slip-trailing (Shiborigaki/Itchin): A technique of drawing lines by squeezing clay slip or pigment from a pipette or tube.
11. Pour Painting (Nagashigaki): A technique of creating dynamic lines by pouring slip or pigment.
12. Pour Glazing (Nagashikake): A technique of partially or layer-by-layer pouring glaze with a ladle or similar tool.
13. Finger Pressing (Yubioshi): A technique of pressing the clay body with fingertips to create rhythmic indentations and protrusions.
14. Faceting (Mentori): A technique of shaving off the outer circumference of a vessel with a knife or thin blade to create polygonal shapes.
15. Board Beating (Itauchi/Tataki): A technique of beating the surface of a vessel with a wooden board or beating tool to tighten it and transfer patterns.
16. Relief (Ukibori): A technique of carving away the area around a pattern to make it stand out three-dimensionally.
17. Carving Out (Hori-dashi): A technique of forming a vessel by carving out the inside and outside from a block of clay.
18. Raised Decoration (Moriage): A technique of creating three-dimensional patterns by thickly mounding slip or pigment.
19. Mold or Stamping: A technique of transferring three-dimensional patterns by pressing carved molds or stamping tools.
20. Applied Decoration (Haritsuke Moyōgata): A technique of attaching decorative clay parts cut from a mold to the vessel body.
21. Spray Glazing (Fukigusuri/Spray): A technique of applying glaze in a mist using a blowpipe or sprayer.
22. Divided Painting (Nuriwake): A technique of dividing areas and painting with multiple glazes or pigments.
23. Layered Glaze (Kasanegusuri): A technique of applying different glazes one over another to achieve complex colors.
24. Splatter Glaze (Uchigusuri/Himatsugake): A technique of scattering dot patterns by flicking glaze with a brush or bundle of twigs.
25. Molded Glaze (Oshigatagusuri): A technique of controlling glaze thickness and patterns using molds.
26. Overglaze Painting (Uwagaki/Uwaetsuke): A technique of painting with overglaze pigments on a fired glaze surface.
27. Mid-layer Painting (Nakagaki/Shitaetsuke/Chukanegaki): A technique of painting between the clay body and the glaze, or between glaze layers.
Conclusion
The history of pottery is nothing less than the accumulation of countless failures and diligent explorations woven by earth, fire, and human wisdom.
This manuscript, left by Mitsuo Kano over half a lifetime, transcends mere scientific data and technical transmission. It breathes the soul of a master artist who, while respecting materials and deeply learning from tradition, ceaselessly sought his own expression. "Onkochishin" (learning from the past to create something new) — we believe that correctly understanding the essence of the sweat and effort of our predecessors, and receiving this baton of spirit and technique, is the path to nurturing a richer ceramic culture for the future.
We sincerely hope that you will utilize this document as an irreplaceable guide for your daily pottery work, research, or art appreciation, and help carry it into the future. Our store, "Antique Liquor 1926," wholeheartedly wishes for the wisdom left by our predecessors to blossom into new beauty and to be passed down through generations, transcending time and borders.