3.8 Preparation for Glazing

Firing in Jingdezhen

Glazing in the Raw-Clay Stage - Glazing to raw clays is usually fired in a single operation at the mature temperature that eliminates bisque firing and cost less in labor and power. It is still a very common practice in China. But only if handled properly, a single firing would have a better union between the clay body and the glaze. However, the raw-clay pot is much more fragile and contains a certain amount of moisture, which makes it challenges for handling and glazing. Thin and delicate pieces are not recommended for dipping or pouring, instead of spraying will be more suitable to prevent high moisture absorption, that will cause slumping or cracking. If dipping or pouring, glazing should be applied quickly to avoid uneven water absorption. If Spraying, glazing should be applied slowly to allow time building up coating and surface not getting too moist. Glaze with a high amount of clay content tends to fit with the body and work best in a single firing.

Glazing in the Bisque Stage -  Most potters would have bisque firing at low temperatures before glazing firing which makes the pots stronger to be handled in the glazing operation. Bisque firing is recommended at cone 010 (900c), which is sufficiently porous to absorb glaze. If bisque firing is too high, that will make it difficult to absorb glaze. The techniques of glazing bisque are dependent on the size and construction of a pot, small size of pots are best for dipping, bigger or more complicated structures are suitable for pouring or spraying.

After glazing, pots are ready to be fired at a higher temperature. However, the bisque firing for high quality like Bone China or fine porcelain ware is exceptionally fired higher than normal temperature. Due to that Chinaware with thin walls tends to be warped easily, so their bisque firing is designed to reach in high or maximum temperature. Meanwhile, the wares are also supported with fireclay rings inside their lips or stacked upside down during firing in order to minimize deformation. Later, the bisque Chinaware is glazed and then re-fired to lower temperature on their own foot. This process would reduce the warping rate since the form is matured earlier at a higher temperature.

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