The filling of purple pottery is a continuous and complete process, and the concrete steps are divided into spreading, mud pressing, scraping, etc. One of the key steps is rarely mentioned. There is little introduction in the text. This step is exhaust. If this step is not done well, the whole purple pottery work will be wasted.
Mud filling is to fill the pre carved groove with colored mud, because the groove itself is full of air. After applying the color mud, part of the air is discharged, but some air is pressed in the groove by the color mud. This situation is more prominent in the large area of the groove or block surface, you can clearly see a bulge on the surface.
The air that is pressed under the color mud must be completely discharged, otherwise, when it is fired into the kiln, the residual air inside will expand when heated, and it will easily generate bubbles, or even explode.
The method of exhausting gas is not difficult, but it requires patience, care and experience. Use a sharp needle to prick dense holes where there may be residual air to let the air out of these holes naturally. Why can the air be discharged naturally?
The color mud used in mud filling is very wet. As time goes on, the color mud gradually dries and its volume shrinks, which will squeeze the air inside, so the air is discharged along these dense pores.
When puncturing a small hole, you should pay attention to it, especially the strength should be just right. If the strength is too strong or too deep, it is likely to pierce the ceramic body and cause damage; if the strength is not enough, if the depth of the air hole is not enough, the gas can not be completely discharged.
Therefore, it is safer to pierce dense holes on the whole surface of the mud filled block. Even if some parts are not deep enough, there will always be enough air to discharge. However, it is a test of patience and care. It can not damage the pottery, but also ensure that the air is completely discharged. Only when the mind is calm can we persist in finishing the dense holes and do the best.