How to make high-grade purple sand

When we talk about the teapot that is popular nowadays, I'm afraid that people are most concerned about sand, because they are scared by the false teapots or teapots that add health chemicals, and suffer from the "purple sand phobia." In fact, all Zisha craftsmen who have a face and face will not do this kind of deeds. After all, Zisha is not as scarce as raw materials such as Xinjiang Hetian jade and precious gems. It is less precious, and those responsible purple sand craftsmen naturally do not need to Raw materials and hands and feet.

Zisha raw materials are neither scarce nor precious, but the preparation process is time-consuming and cumbersome. In order to dispel the doubts of some consumers of purple sand, we will combine the research on the topic of “Chinese Folk Art Market and Case Study: Zisha Art Research”. We will start from the most original purple clay to see how high-grade purple sand is refined. "It is.

Raw ore: can be divided into purple mud and green mud

Talking about the purple sand raw materials, we must talk about Yixing clay. There are many types of clay in Yixing, which are usually divided into three categories: clay, mud and mud. A clay is a kind of variegated silty clay that is dominated by purple. It is an unweathered shale that is deeply buried in the ground. It is also called “stone bone” and is mainly distributed in Dachaoshan, Lanshan and Nanshan in Yixing. Huang Longshan and other places. The purple clay is a mixture of mud and mud in the nail mud and then hand-selected. It is often referred to as “mud mud”. It is the main raw material used for making purple sand pottery, mainly including purple mud, red mud and Green mud.

Purple clay: Purple clay commonly known as "aquatic mud", "red brown mud", "bottom groove blue mud", "big red mud", is the main raw material for making teapot, deep hidden in the Huanglongshan rock several hundred meters below, In the "a clay" seam, the ore body is thin and lenticular, and the rock type is silty mudstone, containing more iron. Because of the different distribution of mineral beds, the range of firing temperature is wide, but the optimum sintering temperature is about 1180°C. Therefore, the purple clay has a reasonable natural chemical composition, mineral composition and process characteristics, and a single clay can be made into various purple clay pottery products through processing and refining. The purple mud as the main material, and other purple clay soil mud, or in combination with other Yixing clay mud, process performance is not changed, mainly to change the hue, grain and appearance characteristics.

Green mud: Green mud is commonly known as “this mountain green mud”. The original ore is pale green, and it has a pear skin color (beige) after firing. It is a small amount of clay in the purple clay layer. It is very rare, usually only when the purple clay is mined. Only mining green mud comes with it. Green mud is sometimes referred to as "mud mud" or "segment mud" because green mud and purple mud are mixed and mixed together. According to the ratio of green mud and purple mud, the color is from beige to brown after firing. The temperature is low) and it turns brownish (middle temperature) until it becomes bronze (high temperature). Since the amount of green clay is not large, and large green clay products are not easily burned, green clay is used only for making small products, or as a make-up clay for the decoration of the surface of the purple mud blank for decoration purposes.

Red mud: red mud is sometimes called "little red mud", "Zhu mud", "stone yellow mud." The ore is yellow or yellow-green and becomes large red, reddish, scarlet, and pale red after firing. The red mud layer is located at the bottom of the tender mud layer, and the original ore that is a “stone yellow mud” is golden yellow; the original ore that is a “Zhu mud” or “little red mud” is a light yellow-green color, and is a dense block, which is a kind of clay. The main mineral composition of yellow-green silty clay rock. Because of its high shrinkage rate and low firing temperature, red mud is often used to make small objects and make-up clay, or as a decoration for the surface layer of purple clay blanks.

Traits: Good plasticity, high green strength

Zisha mud is a unique raw material of Yixing, its reasonable chemical composition, mineral composition and particle composition, as well as technical properties such as good plasticity, high green strength, and small drying shrinkage. It provides good process conditions for the production of Zisha pottery.

The main chemical composition of the purple clay is silica, alumina, iron oxide, titanium oxide, calcium oxide, magnesium oxide, potassium oxide, and sodium oxide. The chemical composition reflects the process performance of the mud to a certain extent, including Plasticity, shrinkage properties, firing temperature, color after firing, etc., such as Fe2O3 content is different, the color is not the same: under normal firing conditions, Fe2O3 content ≤ 0.8%, white after firing; content is 1.3% After firing, it was gray; content was 2.7%, pale yellow after firing; content was 5.5%, light red after firing; content was 8.5%, red after firing; content was 10.5%, after firing Dark red.

In addition to the chemical composition, the properties of the purple clay are also related to the mineral composition. The main mineral composition of a clay is hydromica, and contains unequal amounts of kaolinite, quartz, mother rock fragments, and iron. It is a clay-quartz-mica symbiotic colored clay that is calcined to produce residual quartz and mica. Residues, mullite crystal phases, and hematite have formed a unique single-phase sintering and dual-porosity phase structure of ceramic materials.

In addition, the special particle composition of the purple clay also determines its performance. The particle composition of the purple mud refers to the percentage by weight of particles of different sizes in the mud. If there are many fine particles in the mud, the plasticity is good, and the drying strength is also high, but the shrinkage rate increases accordingly.

The chemical composition, mineral composition and particle composition above the Zisha mud determine its various plasticity, bonding, thixotropy, shrinkage, and firing properties.

Preparation: the process is detailed and sophisticated

The purple clay excavated from the seam is commonly known as “raw mud,” and the mud resembles a block of rock. It is piled in the open air, weathered, and allowed to loosen. Then it is crushed with a hammer crusher and crushed with a wheel mill. Feed through 60 mesh screen (muddy material is too thick, making it difficult; if it is too thin, it is easy to stick hands when it is made, and the shrinkage is large after firing), wet water is passed through the vacuum mud machine to knead, and it becomes a supply Slurry used for making blanks. However, during the Ming and Qing Dynasties, the design and methods for the extraction and processing of Zisha clay ore were very simple. With the advancement of the times and the development of science and technology, the method of crushing the purple clay mud from small grinding mills to stone wheel grinding, and from stone wheels to mechanical processing, greatly reduces the labor intensity of workers and the working environment has also been improved.

Weathering: After the mined purple sand raw material enters the factory, it must be stored in the open air for a period of time (more than 3 months) and allowed to wind, rain, and sun. The purpose is to break down, dissolve and oxidize the raw material through weathering. . Of course, the longer the weathering period, the better. The weathered clay has the following characteristics: clay texture becomes finer, plasticity increases, water content in the raw material is even, some alkali metal and alkaline earth metal salts dissolve, and the refractoriness increases. The weathered raw materials must be manually removed of harmful impurities before the ingredients. According to the quality requirements of different products, the appearance of the raw materials can be visually observed with the naked eye to select materials.

Ingredients: The raw materials used in the production of purple sand pottery are commonly used in purple clay, red mud, and green mud, and a single mud formula is usually used for production, and different mud materials are used for different products. The basic color of purple clay is three kinds of purple, red and yellow. To enrich the appearance of purple clay pottery, to meet the needs of process change and production design, the purple sand technologist sometimes adds appropriate colorants (such as MnO2, etc.) to several mud materials, adjusts and controls the firing temperature and atmosphere, and makes products After firing, it shows a variety of colors: purple or not, or red, but not green, or green, not tender, or yellow, not petite, or grey, not dark, or black and not ink. If the mud material is mixed with coarse sand and steel sand of different particle sizes, the beads will appear after the product is burned, resulting in a special texture.

In addition, the mud is very particular about the different mud materials, adding the right amount of oxides, will produce a variety of color changes, the formation of many new types of mud, such as mud, cinnabar, vegetable eggplant mud, beans blue mud, Dark green mud, azure mud, green mud, bright yellow, yellow mud, red mud, gold osmanthus mud, Dahongpao mud, red mud, Zhu mud, black iron sand and so on.

Smashing: The pulverization of the mud is usually divided into coarse and fine crushing: coarse crushing is usually performed manually when the ingredients are spread, and a jaw crusher can also be used. In the case of fine crushing, a round roller or cage crusher is generally used. The roller mill uses the relative movement of the grinding wheel and the mill wheel to repeatedly roll the material on the mill wheel, and also acts as a mixed mud.

The billet fineness is determined according to the variety, usually 40 to 80 mesh. When the billet grain is fine, the plasticity is improved, the drying strength is large, the firing temperature can be reduced, and the mechanical strength of the product can be improved, but the drying shrinkage and the firing shrinkage are large, and they are easily deformed and cracked during drying and firing.

When the output of the mud material is small, manual processing method or manual method of grinding the clay powder with stone mill is adopted; when the output is large, stone wheel grinding is used to crush, the processing fineness is controlled around 60 mesh screen, and the wet mud is passed through the vacuum mud. Machine mud, become the mud used for making blanks.

Aging: Aging, also known as “ducking mud,” is the practice of stacking mud in a dark, damp, warm, closed room for a period of time (days to months), allowing the mud to function as a series of physics in a damp, windy environment. , chemical changes, which can improve the performance of the mud, such as uniform moisture wetting, more dense tissue, enhanced plasticity, dry blank strength and mechanical strength of the product, etc., thereby reducing the molding process and the drying of the green Cracking.

Practicing mud: After the obsolete mud material, it is necessary to degasify the mud by vacuum and remove the air in the mud to meet the forming requirements. After the vacuum treatment of the mud, the green body is denser and the air content is extremely low, which improves the plasticity, bonding and the strength of the dried bar, and reduces the cracking after burning. When vacuum mud is practiced, the water content of the added mud should be appropriate, and the velocity of mud addition should be uniform—too fast will clog the vacuum chamber, and too slow will cause the mud segment to disjoin and break. The degree of vacuum must also be properly controlled, typically 700 to 740 mm Hg.

In this way, through the cumbersome processes of mining, weathering, batching, smashing, staleness, and mud training, the production of purple sand pots and other purple sand pottery on the "training" became.

Zisha mud common ingredients method

Select all kinds of mud for processing.

Different muds can be used for matching, and a variety of mud colors can be obtained.

Different colors of mud strips are used together to form a twist, and a variety of colors are used to make the clay.

In the mud mixed with different materials, different colors of particles, resulting in color depth effect.

Mixing and mixing particles of different sizes in the mud to produce a pear skin effect.

Add appropriate amount of coloring oxide to the mud to enrich the color.

Zisha mud common mud situation

1) The mountain green clay is mixed with a suitable amount of purple clay to prepare a mixture of mud.

2) The amount of red mud in Fudong is added into iron powder, and it is made into cinnabar mud, Dahongpao mud, and red mud.

3) The amount of white mud is added to the iron powder and it is converted into Zhu mud.

4) A suitable amount of purple clay is added to manganese oxide to prepare a dark brown color.

5) A suitable amount of purple clay is added with cobalt oxide and manganese oxide to prepare black iron sand.

6) The mountain green mud and a small amount of white mud fight, and then add the appropriate amount of chrome green, prepared into a dish eggplant mud, beans Bi mud.

7) The mountain green mud is matched with a small amount of white mud, and then cobalt oxide is added in an appropriate amount to prepare dark green mud and azure mud.

8) Cobalt oxide is added to the amount of this mountain green clay to make green clay.

9) The mountain green mud and a small amount of white mud fight, and then add the appropriate amount of chrome tin yellow, modulation yellow, yellow mud, red mud, gold osmanthus mud.