Using sagger to fire ceramics can not only increase the loading capacity, prevent products from sticking and improve the yield, but also have certain thermal conductivity and thermal stability, which can ensure the quality of ceramics. The shape of a sagger varies with the shape of an object. The eggshell black pottery fired during the Longshan culture period in China used a special sagger.

It can be divided into two types: large container and small container. The small container sagger consists of container wall, also known as container ring and container bottom. The process of making the box wall is roughly as follows: first, take several pieces of special iron sheets, pass them through with thin rope along the thickness direction of bamboo sheets, and the two ends are closed to form a ring tube, the inner side is fixed with iron rings, and the outer side is tied with ropes. Then the outer wall of the ring cylinder is coated with box mud, the cloth is dipped in water to smooth the outer side, and then trimmed and shaped with iron sheets.

A large sagger consists of a straight wall and an inclined wall. The method of making a straight wall is similar to that of making a small box wall. The manufacturing method of inclined wall is similar to that of drawing porcelain blank, but because of the coarse particles of box mud, water operation is needed during trimming and molding. After the straight wall and inclined wall are finished, they are bonded with box pulp.

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A kiln furniture. In the process of firing ceramics, in order to prevent gas and harmful substances from damaging and fouling the green body and glaze, the ceramics and green body are placed in a container made of refractory materials, which is called a sagger or box. Refractory materials for manufacturing industrial saggers include mullite, corundum mullite, alumina, etc.

The prepared bowl blank is still green, commonly known as clay box, which can't be used to burn porcelain blank. Only after the earthen box is electroplated and baked into a sound box, that is, a cooked box, can it be used to fire porcelain blanks.