The ashing process is mainly to fire the teapot with high iron content in reducing atmosphere to change the form of iron oxide in raw materials. Under normal firing conditions, most of the crystal formation of Zisha iron oxide is that hematite is fired in reducing atmosphere, and hematite is reduced to magnetite crystal, so the surface of ash-covered products has a certain adsorption effect on magnets.

Some mud materials with low iron content, such as green mud, are generally not suitable for cover ash firing (after cover ash firing, it is mostly light gray and dark, and the color effect is poor). If the earthenware pot covered with ash is re-fired in a kiln with neutral oxidizing atmosphere, it will return to its original color.

As early as the Ming Dynasty, Chen Zhongmei, a master of purple sand craft, had used the methods of sand adjustment and spreading to enhance the decorative effect of the surface of purple sand utensils.

2. Sand adjustment process

In the treated slurry or powder, various sand particles with a certain size and proportion are added as needed to improve the particle density.

The transferred particles and base mud belong to the same mineral aggregate, which is called acoustic sand; The transferred particles and the base mud do not belong to the same mineral aggregate, which is called abnormal sound sand.

When natural sand is mixed into the original mud, the color of the tire will not change much after firing because of the same quality of the mud, but the particle content in the base mud will increase, which mainly plays a role in strengthening the green skeleton. For some soft particles, it is necessary to bake the particles at 600-800℃ to increase their strength, otherwise the particles are easily crushed by tools during the molding process, resulting in tailing on the device surface.

For example, the shrinkage and deformation rate of most Zhu clay materials are relatively large, which is not conducive to the independent production of large-scale works. It is necessary to increase the strength of the green body by sand adjustment, so that the overall shrinkage deformation of the green body after firing is reduced and the firing yield is improved. Therefore, most of the pottery pots seen in modern times are mixed with coarse sand, or supported by clinker (clinker is the powder made by grinding the finished clay after firing).

Different shades of sand will produce different color effects because of the different colors and qualities of transferred particles and base mud. If the transferred particles are hard, the particles on the surface of the device are prominent after firing, showing a thick pear skin shape; When the particles are soft, fine pits will be produced on the surface of the device after firing. The softer the graininess, the more obvious the pits are, forming a texture effect similar to orange peel.

4, sand laying process

Sand spreading refers to spreading sand particles with different mud colors and dots on the surface of the purple sand body under a certain humidity in the process of making it. Then use tools to embed sand particles into the surface layer of the green body. Sand laying mainly plays the role of ornament and decoration, so that the sand spots on the surface of the fired purple sand ware are in sharp contrast with the tone of the tire.

Generally, it is required that the quality of sand particles is higher than or equal to that of green particles. If the quality is soft, it will lead to the tailing of particles during production, and the particles will shrink greatly after firing, which is incompatible with fetal quality.

5. Sand pumping process

Sand pumping is to separate particles with certain specifications from processed powder or mud. 60-80 mesh particles are extracted from 40 mesh powder, so that the remaining particles and fine materials form obvious thickness contrast effect after firing, resulting in new texture.

Extended data:

Usage characteristics:

(1) Purple sand is a kind of porous material with double pore structure.

Fine pores and high density. Make tea in a teapot without losing its original flavor.

(2) The teapot has good air permeability.

Using it to make tea is not easy to go bad, and the more you stay in summer, the worse it is. If you don't use it for a long time, it won't smell. Just store the boiling water first, pour it out immediately, and then soak it in cold water to wash it, and your vitality will be restored, and the tea will still taste the same.

(3) The teapot can absorb tea juice.

The inner wall of the pot is not brushed, so there is no odor in making tea. After long-term use, the wall of teapot accumulates "tea rust", which makes the empty teapot full of boiling water, which is related to the porosity of teapot embryo, which is the unique quality of teapot.

(4) The teapot has good cold and hot mutation performance.

In the cold winter, boiling water is injected into the pot and will never burst due to sudden temperature change. At the same time, the heat transfer of sand is slow, so it won't be hot after making tea. And it can be cooked and heated on slow fire without being cracked by fire.

(5) The longer the purple sand is used.

The color of the pot body is getting brighter and brighter, and it looks like Wen Ya. The teapot has been used for a long time, and its body will become smoother and more lovely because of touching and wiping.

Baidu encyclopedia-teapot