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Firing Technology

Firing Technology of Dehua Ceramics

The firing technique of Dehua porcelain is a local traditional handicraft in Dehua, Fujian. Dehua porcelain sculpture began in the Song Dynasty and has never been interrupted, forming a unique traditional craft. One is to use high-quality kaolin to shape it directly, and the other is to turn the clay into a mold and then inject grout or rubbing. Decide whether to glaze it according to the needs, and then put it into the kiln and fire it at a high temperature of more than 1,000 degrees. Fusion, showing the temperament of a famous kiln, especially the white porcelain products with distinct shades, rich layers, milky white glaze color like creamy fat, and excellent light transmittance.
"The world's white porcelain looks at China, and the Chinese white porcelain looks at Dehua." Dehua white porcelain is known as "China White". Dehua porcelain has the characteristics of good whiteness, high gloss, strong stability, temperature resistance, pressure resistance, wear resistance, and corrosion resistance. It also has physical and chemical characteristics such as pure and moist glaze color, high density, and good light transmittance.

  • Embryo
  • Ceramic
  • Ceramic
  • Kilning

Firing Technology - Blank Preparation, Porcelain Clay Processing

The clay material of Dehua ceramics is mainly composed of quartz, feldspar and kaolin, which are mostly mixed by special China clay suppliers, mainly in the following links:

1. Grinding, panning

The China clay ore material excavated in different places is put into the stone trip-powered trip-powered machines in a certain ratio and mashed until it is powder. The crushing methods used in different periods are not the same, the Tang Dynasty is to crush the porcelain clay with feet, the Song Dynasty began to crush the porcelain clay with water driven water wheel, and the modern useful mechanical crushing also uses electric power to crush the stone hammer. The crushed porcelain clay powder is poured into the washing tank, stirred in all directions, and then precipitated.

2. Stale, mud

The porcelain mud after repeated washing is piled into the stale tank, and the humidity is maintained to make it ferment and rot to increase the viscosity of the porcelain mud. This process takes more than half a month. Mud practice is to remove the porcelain mud in the stale pool, toss and turn several times to stir, in the process of throwing the porcelain mud into piles, while falling and beating. When the amount of soil is small or to make fine products, the foot or hand kneading method is used for mud training. The purpose of mud training is to make the mud uniform and improve the density and plasticity of the mud.

Firing Technology - Molding Production, Exquisite Workmanship

For the prepared clay material, through certain methods and means, it is deformed, and becomes a beautiful shape and smooth line, or becomes a vivid and ingenious sculpture handicraft. There are two kinds of molding production: manual molding and mechanical molding.

1. Manual molding, there are hand pull blank, impression, wheel molding, hand molding, hand kneading, sculpture, grouting and other molding methods.

① The method of forming billets by hand is the method of manually drawing the plastic mud material into various shapes of billets on the rotating roulette wheel.
② The impression forming method is to put mud into the impression or make the impression into a shield and put it on the pulley pulley to rotate the die.
③ The wheel molding method is a technique of putting mud on a special roulette plate and using the centrifugal force generated by the rotation of the roulette plate to form the blank body. This method is mainly used to make various circular devices.
④ Hand molding method is a technique of directly pressing the appropriate amount of mud into the mud mold with the hand and compacting it with the finger. This method is mainly used for the printing of small utensils and decorative accessories.
⑤ Hand molding method is to take an appropriate amount of mud material directly by hand molding, and this method is used in the accessories of objects and sculptures.
⑥ The sculpture molding method is to knead the body structure of the creation subject matter with mud material, and then use bamboo carving knives, iron carving tools and other sculpture tools to sculpt and sculpt each part. The sculpture process is a pure manual artistic creation technique, which continues to this day.
⑦ The grouting forming method is to stir the mud with water or directly inject the stale mud into the plaster mold, and then make the billet by absorbing water and drying it.

2. Mechanical forming, knife pressing, rolling, dry pressing, isostatic pressing and other forming methods.

① Knife molding method is based on wheel molding, in order to improve production efficiency, diesel engine, motor and other machinery as the power to drive the compact machine, press molding.
② Rolling forming method is improved on the basis of knife pressing, and the rolling head is tightly pressed when forming the billet mud.
③ Dry pressing forming method is to dry the mud, become powder and maintain a certain humidity, and put it into copper die stamping.
④ isostatic pressing forming method is to make large, medium and small granular powder through the drying tower, add the binder, send into the copper mold and press the particle compact forming.

Firing Technology - Ceramic Decoration, Icing on The Cake

Usually, people modify the appearance of the ware and beautify the plain surface of the porcelain to express their inner wishes, beliefs and taste of life. There are many ceramic decoration methods, each with technical characteristics and artistic style, mainly body decoration, glaze decoration, underglaze decoration, glaze decoration, glaze decoration and so on.

1. Body decoration

Body decoration refers to the body as the main object of decoration treatment, or directly to the body decoration to complete the entire decoration needs of the method, such as kneading, carving, relief, pile paste, etc.
(1) Kneading, using both hands to knead porcelain mud into strips or blocks or balls, and then pile molding into the shape of the work, and then kneading details according to the structure of the work. Kneading is often used in the main body modeling, as well as the production of subsidiary parts such as hands and feet, clothing patterns, streamers, etc., with both hands, sometimes with bamboo carving knives.
② Meemie, using bamboo meemie pieces as a pen, directly on the blank body into a variety of decorative patterns, the technique is light and concise, free and unrestrained. After the glaze is burned, the glaze color is deep and the pattern is obvious.
③ Relief, the use of sculptural techniques, so that the pattern of high floating on the surface of a decoration. Ming Dynasty ivory white products multi-style plum blossom cups, pen holders, incense burners, vases, teapots, etc. are decorated with relief, since the Qing Dynasty continued to use, enhance the three-dimensional sense of decorative patterns.
④ Pile paste, also known as kneading flowers, is a traditional decoration technique in the early days of Dehua white porcelain, which first uses molds or hand-kneaded accessories, such as flowers, animal heads, etc., pile paste on the blank trunk, and then trim and shape. It is widely used in furnishing art porcelain. So far, where there are products such as flower baskets with pinched porcelain flowers, the flowers and stamens on the walls of various flowers and branches and leaves are also made with pasted hair, the flower shape is changeable, the flower pieces are like silk, and the shape is realistic.
⑤ Through the flower, also known as through carving, hollow, is the main decorative method of carving, using bamboo or metal carving knife to draw a pattern on the formed blank, and then using a thin and sharp blade to cut through the part that does not need to be retained, the manufacturing is extremely fine.
⑥ Carving, floral lines for engraved, floral and the body plane is consistent, after glaze burning, the scratch is filled with glaze, easy to wash, no dirt, clear pattern. Its wide applicability, especially tableware and other daily porcelain square, hook grass, flower pattern decoration is more suitable,
⑦ Pick the flower, in the porcelain body that has been painted with a good pattern pattern, the part other than the pattern is removed with a knife, exposing the plain tire, so that the pattern is raised, like relief. After firing, it reveals a white and pure matte birthmaterial, which contrasts with the glaze light of high purity and crystal, producing a unique decorative art effect.
⑧ Printing, engraved pattern mold and blank body one-time printing, pattern, specifications are consistent, simple and fast, can be mass-produced.

2. Decorate with glaze

Glaze decoration is the application of a layer of glaze, or glaze water, to the surface of porcelain. Glazing is commonly known as "glazing" and "dipping glaze" in Dehua. According to the different body is divided into green glaze and plain glaze, in the process of operation should be based on the size of the body, thickness, structure and the performance of the glaze, respectively choose dipping glaze, pouring glaze, pouring glaze, enamelling, brushing glaze, spraying glaze and other glaze methods.
The traditional glaze paste in Dehua is divided into earth glaze and gray glaze. Earth glaze is a glaze with porcelain stone as a single formula, and gray glaze is a mixed glaze with porcelain stone and limestone, grass and wood ash. According to the characteristics of the glaze, there are transparent glaze, milky glaze, color glaze, bright glaze, matt glaze, crystal glaze, sand gold glaze, grain glaze, pearl glaze, artistic glaze, glaze painting and so on.

3. Underglaze decoration, on glaze decoration and in glaze decoration
① Underglaze decoration, commonly known as underglaze color, is the use of underglaze color through a variety of decorative techniques in the green or plain on the decoration, and then covered with transparent glaze or translucent glaze, and then fired at high temperature. The main varieties of underglaze painting are blue and white, rust flowers, underglaze red, underglaze multicoloured, applique, printing spray color, brush flower and so on. Among them, underglaze blue and white is a precious traditional art in China's ceramic decoration, which mainly uses cobalt oxide as a color agent to paint and dye on the blank body, and then apply transparent glaze into the kiln; Underglaze wucai is a variety of underglaze colors painted on clay or plain fired blanks, and then glazed into the kiln, high temperature once fired.
② Glaze decoration, commonly known as glaze color, refers to the method of decoration processing on the glaze of the product after firing. After adding color by painting, decal and other methods, low temperature color burning is carried out. Dehua enamel painting decoration techniques mainly include ancient color, pastel, new color, spot glaze, electric luster, spray, printing, decal, titanium plating and so on.
③ Glaze decoration, commonly known as glaze in color, refers to the decorative color in the glaze layer, in the bottom glaze on the blank or the surface of the glaze burned products for color decoration, after applying thin layer glaze, and then with the blank once fired or lower than the glaze burning temperature for two color burning, after burning the material penetrates into the glaze layer inside, the glaze closed after cooling, forming glaze in color.

Firing Technology - Kiln Loading, Emergence into Porcelain

1. Kiln

Kiln is an important facility for clay to be fired into porcelain at high temperature. Dehua began to use kiln to fire porcelain since the Shang and Zhou dynasties. It has a unique structure, unique firing technique and superior quality. Lin Bing, the arch kiln master in the Song Dynasty, was honored as the "God of kiln". He devoted his life to the research of kiln construction techniques, and took pains to teach kiln workers to build kilns. Later, he was invited to Jiangxi to teach his skills and died in a foreign land. Through archaeological excavation, there are three typical kiln types in the history of Dehua kiln, namely, dragon kiln, divided chamber dragon kiln and class kiln.
① Dragon kiln, Dehua folk called "snake kiln", is the most important and earliest type of kiln for ancient porcelain firing in Dehua Kiln. Generally built on the slope of the mountain, from the bottom up, it looks like a flying dragon falling from the sky, and like a long snake winding on the hillside. Its length is generally 20-60 meters, which is composed of three parts: kiln head, kiln chamber and kiln tail. The kiln head has a fire chamber and a ash pit, and the kiln chamber is divided into several sections (called "mu" in dialect), and the kiln door is arranged on both sides of each purpose as a furnace loading and oven passage. The kiln door is built next to the kiln wall (called "kiln milk" in dialect), with a firewood hole and a fire eye, the firewood hole is used for firewood heating, and the fire eye is used for placing a temperature scale or fire light to observe and determine the heat in the furnace. There is a fire wall at the end of the kiln, and a row of smoke holes at the bottom leads to the chimney. When the kiln is fired, the height difference between the front and the back is used to make the flame rise naturally, and the flame is constantly pushed backward and upward to make full use of the waste heat during the heat wave rise. Because of the simple structure, large capacity, fast rising and cooling and fast flow rate, the dragon kiln can create a reducing atmosphere, so that the temperature distribution in the kiln chamber is more uniform, so the kiln failure is less and the yield is higher.
② Divided chamber dragon kiln, Dehua folk called "chicken cage kiln", is a kiln structure of the transition development of dragon kiln to class kiln, each kiln chamber is a separate roof, the top is like eggshell or steamed bread, and the appearance is like a chicken cage connected together. On the basis of the dragon kiln, increase the volume, the kiln chamber is divided into different chambers, and there are also three parts: kiln head, kiln chamber and kiln tail, the kiln head has a fire chamber, and the kiln chamber has parapet walls on both sides. Chicken coop kilns appeared in the Song and Yuan dynasties when the porcelain industry of Dehua was flourishing, and the amount of loading and firing was much larger than that of dragon kilns. The Qudougong kiln excavated in 1976 is a representative of the divided chamber dragon kiln used in the Song and Yuan dynasties, which is a typical inverted flame kiln structure.
③ The class kiln, also known as the "big kiln", was built in the late Ming and early Qing dynasties, built on the mountain, the slope is usually between 10-15°, generally composed of 3-9 kiln chambers, the bottom of the kiln is flat, the rear kiln chamber is slightly higher than the front, forming a step, the kiln chamber from nine to dozens of levels, the height from 2 meters to more than 4 meters, a huge scale. The technique of building class kilns was introduced into Japan during the Ming and Qing Dynasties. Since the Qing Dynasty, the Japanese have always regarded the Dehua Kiln as "the ancestor of the kiln". In 1907, after inspecting the kiln of Dehua Kiln, the Japanese Yayiro Kitamura believed that "the kiln of Dehua and the kiln of Japan are exactly the same, even if they are slightly different in structure." If Japanese kilns were imported from Fujian Province, Dehua Kiln should be the source." Japanese ancient ceramics expert Suzuki Miyosan wrote in the book "Kiln" : "Generally speaking, the string kiln refers to the kiln that is built on the ground and tilted upward, and this type of kiln also has two types of tunnel type and connected chamber type, and both are called string kiln. In Japan, only the connected chamber type is called string kiln, which is probably indirectly spread from Fujian Province in China, and the Dehua kiln in Fujian Province is estimated to be the ancestor of string kiln."

2. Kiln loading

Kiln workers in the blank production, drying, glaze, the porcelain blank piece by piece into the kiln ready to fire, this is the kiln. This is another crucial step in the firing process.
Before loading the kiln, it is necessary to check the kiln, especially the integrity of the kiln wall, find problems, repair them in time, and clean the kiln, the bottom of the kiln is flattened with soil, and a layer of China clay sand or husk ash is scattered, or the fixed saggar is used as the bottom of the kiln. According to the shape of the utensils and the different kiln utensils, it can be divided into overlapping burning, opposite burning, normal burning (saggar burning), set burning, overburning, branch burning, cushion cake burning and so on.
Take the saggar as an example. The saggar is very important in the kiln. At the bottom of each column are several well-cooked, previously burned ones, and the new ones are placed on top. The saggar mouth is usually high on one side and low on the other, respectively, hard mouth and soft mouth, which should be rotated and adjusted when installed into a column, and hard mouth and soft mouth are installed straight. The less valuable products of the same kiln are packed at the head of the kiln (the "cold eye"), or in the saggar at the bottom of the column; High-value products are installed in a better kiln position, that is, the main space in the kiln.
Kiln loading is physical work, less attention from ancient times, but the kiln is a great deal of knowledge, through a lot of scientific principles, such as after the kiln temperature rises, affected by the utensils and saggar, the saggar columns around will produce a slight tilt. Therefore, when loading the kiln, it must be noted that the lower part should be installed correctly, and the upper part should gradually tilt to the center, so as to prevent the tilt caused by high temperature and collapse, at the same time, to ensure the stability at high temperature, a certain gap should be maintained between the columns, and the gap should be uniform, and the saggar column should be packed firmly with broken saggar pieces.

3. Burn

Also called kiln, is another important link in the firing process. After the completion of the kiln, all the kiln doors, firewood holes and temperature observation holes should be sealed with kiln bricks and mud slurry, that is, the kiln is sealed. After sealing the kiln, you can choose a good time to ignite the kiln.
Before ignition, the kiln owner must determine the required fuel according to the kiln structure. The fuel used in ancient Dehua kiln firing is mainly pine wood and pine branches, supplemented by miscellaneous wood. Pine wood contains turpentine, burning large firepower, high temperature. Traditional dragon kilns, chicken coop kilns and class kilns all use pine wood as fuel. Before the ignition, the kiln owner should also follow the traditional customs of folk kiln firing and hold a ceremony to worship the land public and the kiln workers.
According to the different firing atmosphere, the traditional kiln in Dehua can be divided into two kinds: reduction flame and oxide flame. According to the analysis of archaeological data, most kilns in Dehua from Tang and Song Dynasties to the middle and late Yuan dynasties were fired by reducing flame. After the end of the Yuan, a large number of oxide flame burning.
A reduction flame is an incomplete combustion flame in which carbon monoxide and hydrogen are abundant and no or free oxygen is present. The reduction flame can fully reduce the iron trioxide (Fe2O3) in the body of the billet into ferrous oxide (FeO), become cyan, eliminate the phenomenon of porcelain yellow, so in the kiln process of daily porcelain, the reduction flame is mostly used. Oxide flame refers to the flame of complete combustion of fuel, there is a large amount of air supply, sufficient oxygen in the kiln, less carbon monoxide, in order to make the water and all organic matter in the billet evaporation and volatilization discharge, so that the billet body to get normal shrinkage, so in the kiln process must have the oxide flame stage. seldom
The kiln starts burning from the fire chamber of the kiln head, and the small fire lasts for 7 to 8 hours to preheat. Then start to add wood, the fire ignited, the kiln temperature immediately began to rise, about 3 to 4 hours later, the kiln master from the observation hole to check the temperature scale (also known as "fire light", commonly known as "light"), check the temperature and atmosphere in the kiln. Once it is confirmed that the fetal glaze has reached the positive firing, that is, the kiln head stops adding wood, only casts fine wood to burn a small fire, and begins to open the first kiln chamber to cast wood, increase the fire from the first kiln chamber, until the eighth kiln chamber reaches the temperature, the first kiln chamber to cease fire, move to burn the second kiln chamber, and so on.
During the kiln firing process, the cold air must not be allowed to enter the kiln chamber, and the utensils will suddenly burst when they contact the cold air, so when burning up by section, the kiln head should constantly add pine branches to burn a small fire to protect the temperature. The whole firing time, the kiln is dry in autumn and winter, the water is less, and the firing time can be shortened to about 22 hours; In spring and summer, the kiln is wet and more moisture, and the firing time needs to be increased to about 30 hours.
Each process and each step of the kiln process embodies the summary of the experience of the kiln artisans over the years.

4. Exit the kiln

Coming out of the kiln is the moment when the kiln workers work hard and look forward to it. After the kiln ceasefire, the cooling time takes about 3 days, that is, 3 days after the ceasefire, the kiln can be opened to produce porcelain. When going out of the kiln, it is necessary to start with the saggar around the kiln door, and then put a row of saggar columns behind the firewood ditch out of the kiln. The kiln order of the saggar is generally taken from top to bottom, and both hands should be matched well to prevent the breakage of the old saggar from causing the fall and damage of the utensils.

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