To make a piece of Jianshui purple pottery requires ten to more complicated processes. Except for firing, all or most of the other processes have to be done by hand. Therefore, it is impossible for Jianshui purple pottery to be made by one person. It is the result of the cooperation of several people. In the traditional production process of Jianshui purple pottery, it is generally divided into eight procedures: mud making, casting, drawing, blank cutting, mud filling, finishing, firing and grinding, and each process is produced by a specially assigned person. Therefore, it is particularly important to maintain the integrity of Jianshui purple pottery art in the production process. Often an excellent ceramic creation ideas due to the mistakes of participants in the production process, resulting in the failure of creation. This requires the creators (ceramists) to be fully familiar with each process and strictly require the participants to work according to the design intent.
Jianshui Zitao original slime is mainly produced in Wanyao village, two kilometers away from the county seat. It is distributed in Tertiary strata, with an area of about 0.15 square kilometers, visible thickness of 0.54-11.54 meters, and general thickness of 4-6 meters. The content of silicon oxide and iron oxide in the clay is particularly high, and the quality of the products is far better than that of other places. The reserve initially provided is 721000 tons. ④ The mined soil is fine and hard, so it is necessary to spread out and place the massive mud of different sizes and dry them naturally. Then grind it into fine powder with a stone mill. The powder is sieved manually according to the different sizes of large, medium and small sieves until the mineral soil becomes very fine aeolian marl. After sieving, the different powder mortars are mixed according to the requirements of pottery making, and then they are poured into a large pottery jar for soaking and mixing. After placing the grit, the slurry is washed again. After five or six times, it is naturally solidified and dried into “raw mud” in the closed state. After the raw mud is cured, it needs to be placed in the gypsum jar for about a week, commonly known as “awakening mud”. After waking up, trample and stir the clay with feet until the mud is cut off with a trowel, and the cross-section is a fine reflective mirror. It is commonly known as “cooked mud”. At the end of the last century, Jianshui arts and crafts pottery factory set up a mud workshop, using vacuum mud refiner instead of manual mud making process, which changed the situation of Jianshui purple pottery hand hammering mud.
Casting is one of the important procedures of Jianshui purple pottery, which is directly related to the artistic effect of the shape of the pottery. The traditional casting tool of Jianshui purple pottery is a pottery cart. The refined mud is placed on the clay cart, and the clay is pulled into the body by both hands by rotating force. All round ware is formed by casting. Before casting, it is necessary to knead the mud by hand, commonly known as “kneading mud”. The main purpose of the operation is to discharge the residual bubbles in the slurry by hand kneading, and to make the moisture in the slurry further uniform, so as to prevent bubbles, deformation or cracking during the firing process. If the moisture content of the slurry is lower than 23%, its hardness is higher and it is not easy to form. Appropriate water can be added to control the moisture content of the slurry between 24% and 25%, and then the billet can be formed. Due to the softness of Jianshui purple clay and the need for internal and external trimming, the drawn body is slightly thicker. It is necessary to pay attention not only to the shrinkage ratio but also to the shape of the billet. According to different shapes, larger products have to be drawn in sections. From which part is segmented, we can see the quality and level of the casting master’s skill. If the cross-section of the objects is not circular, the method of beating mud can be used.
After the body of Jianshui purple pottery is drawn, it needs to be placed in a cool place until a little moisture is naturally removed from the clay body. After the blank is trimmed, the drawing process is carried out according to the needs. Because the shape and color of Jianshui purple pottery decoration is achieved after drawing, the traditional drawing process of Jianshui purple pottery is only painted with black ink. The similarities and differences between the drawing process of Jianshui pottery and that of Jingdezhen ceramics lie in the following: Jingdezhen ceramics use pigments to draw directly on the green body. Both the overglaze and underglaze colors are in place one step in the drawing process, and then show different colors after firing. However, the color of Jianshui pottery is obtained by filling mud with different color mud prepared in advance after cutting. Therefore, the drawing process only uses single color drawing, regardless of ink color. Moreover, the green body must be kept moist at any time. The same thing is, the traditional painting of Jianshui pottery still pays attention to the painter’s aesthetic cultivation and painting skills, and often the value of the work depends on whether the painting work is undertaken by the famous calligraphers and painters. Although this is biased, Jianshui pottery is an art of pottery with many people’s cooperation. It is different from Chinese calligraphy and painting in essence, but it also reflects the drawing technology for traditional Jianshui pottery art from one side The importance of.
The traditional tool for cutting blanks is a self-made steel needle. Generally, one end of the steel needle is forged and ground into a 1.5cm long oblique edge with a very thin and sharp edge. When engraving the blank, first make a vertical mark along the edges of both sides of the ink mark on the green body. The thinner ink line can directly pick out the mud, while the wider figure needs to be cut point by point until all the ink marks are removed to form a uniform groove at the bottom. It is necessary to keep the green body in a certain humidity during the process of engraving. Generally, plastic film is used to wrap the mouth of the device shape and the part not to be engraved temporarily, so as to avoid water volatilization. The part exposed to the air should be sprayed with water timely to keep the whole green body at a certain humidity as far as possible. Carving blank is the representative technology of Jianshui purple pottery, especially the fine strokes, which need to be as subtle as possible. If the engraving is too deep, the body is easy to crack when firing; if the engraving is too shallow, the image will be damaged after grinding.
Mud filling is an important process to realize the drawing and color change of Jianshui purple pottery. Natural Jianshui purple clay is mainly composed of red and white mud, and other colors need to be mixed with colorants. Each kind of color mud is put in a small bucket, and water is added as appropriate to make it paste. After the clay block is engraved, lift the color mud with iron sheet according to the color requirements of the picture, pat and embed the color mud at the cutting position of the mud block, and smooth the color mud. When the color mud on the inlay is slightly dry, it will naturally sag due to air adsorption, and then it needs to be embedded again for several times until the color mud is firmly combined with the green body. In the process of embedding the clay, it is also necessary to spray water to keep the green body moist all the time, and to press the color mud tightly with iron sheet continuously, so as to remove the air in the mud and ensure the smooth and smooth surface of the finished pottery.
After drawing, engraving and embedding clay, the surface of ceramic body has been damaged, so it is necessary to finish the body. It is necessary to keep a certain degree of dry and humidity for the ceramic body. If it is too dry or too wet, it will damage the inlaid part and the standard of the shape of the ware. In the process of finishing, first of all, carefully check whether there are bubbles in the green body. If there are bubbles, use a cutter to pick them out, and then smooth and compact the mud. For objects with a circular cross-section, you can use the clay car to repair the body. You need to put the clay block on the clay car. According to the shape requirements, you should use various special iron or plastic tools to repair the blank. When repairing, you should pay attention to the stability of your hands and the coordination between the hands and the pottery cart. It is easy to thin and not easy to thick, so as to avoid damaging the figure drawn on the green body. If the cross-section is not round or special-shaped ceramic blank, it needs full manual trimming. Manual trimming depends entirely on the experience of the dresser, and according to the shape of the implements and the requirements of engraving, it takes relatively more time, and the effect is naturally better.
The early firing of Jianshui purple pottery was completed by lighting firewood in a long kiln with a length of several tens of meters. Because the Longyao firing required experienced potters to observe the temperature and fire color, and the yield of finished products was not high. Now gas kiln (liquefied gas) or electric kiln has been basically used. Jianshui pottery is usually fired at 1100 ℃ to 1200 ℃ for about 7 to 12 hours. At high temperature, the clay melts into a liquid and fills the gap between the unmelted particles, which makes the shrinkage coefficient of the clay body higher. The shrinkage rate of Jianshui pottery after firing is about 15% to 20%, so the texture is fine and solid. There are two firing methods of Jianshui pottery: oxidation and reduction.
Oxidation burning means that in the process of firing, there is always sufficient oxygen supply in the kiln chamber, and the concentration of carbon monoxide is low. In order to make the moisture and all organic matters in the green body evaporate and volatilize, so that the green body can get normal shrinkage, there must be oxidation burning stage in the kiln process. The red and white clay of Jianshui pottery is dark red, which is commonly known as “pig liver red”, and the white mud is yellow white with high brightness, commonly known as “ivory white”, and the color change of the objects made by oxidation is small after grinding;
Reduction burning is a case where the temperature in the kiln rises to about 900 ℃, and then the oxygen in the kiln is reduced, which causes the oxygen in the kiln to be anoxia, which leads to the flame need to search for oxygen from the bad body or boron for continuous combustion. When the concentration of carbon monoxide in the kiln is between 2% and 4%, the iron in the ceramic billet will appear brown black during the reduction process. The fire skin after burning with reduction flame shows black brown and blue white. After polishing, the color changes greatly, and the pure black, black and red and gray green colors can be obtained.
Glaze free grinding is one of the important characteristics of the water-building purple pottery, and it is also the most time consuming part of the whole process. The water purple clay is fine and sand free. The surface of the ware can be obtained by grinding technology, such as matte, bright and specular light. The traditional grinding technology of water ceramics is divided into three parts: Fire removing, wire removing and polishing. The surface of newly fired water building pottery is rough and solid as iron, and has a layer of metal luster. This is called “fire skin”. When polishing, it is necessary to use coarse sand stone to dip water to remove the fire skin. The surface of the utensil removed from the fire skin will leave scratches due to the friction of the coarse stone. Therefore, the scratch of coarse stone should be removed evenly with the water of the fine greasy oil stone. This process is called “wire removal”. After the wire is removed, the scratch of coarse stone can be removed Get matte texture. If the effect of bright light is needed, polishing must be carried out. Polishing must be repeated with water covered with white pebbles unique to Jianshui and the surface of straight ware shall be bright until the person is clear. In the grinding process, every step needs to be careful, even force, light grinding and grinding, so as to avoid damaging the surface of the machine.