Firing, Glazing and Decorating

Molds made of plaster of Paris for ceramics class.

       Vessels that are not round are usually cast in molds, made of plaster of Paris, each half of the vessel being made separately and the parts joined together when taken from the molds.

       Pottery is burned, baked or fired in kilns, which vary in size and shape according to the sort of ware for which they are designed. The higher grades of ware are placed in cylindrical earthen boxes, called saggers. The saggers are stacked in the kiln by packing in tiers, one above the other. The ware is usually raised to a white heat, which is maintained for thirty-six hours or more, after which the kiln is allowed to cool slowly. When cold, the ware is taken from the saggers, and in this state it is called biscuit. The rough places on the surface are now smoothed, and other finishing touches are given, after which the ware is glazed.

       The process of glazing is accomplished by dipping the ware in a mixture called the slip. This is a solution of the glazing substance in water and is but little thicker than milk. The ware is dipped in, and on being removed, it is so handled that no drops are left standing on the surface. The porous walls absorb the water and leave a thin coating on the surface, which, on a second firing, passes into the clay and forms the glaze. By the addition of necessary pigments, coloring can also be produced with the glaze. When this is poured on and allowed to ran down until stopped by the heat, beautifully shaded effects are often produced.

       Decorations are usually put on with a brush, either before or after glazing. If decorated after glazing, the ware must be fired a third time. Decorating requires great care and skill, as the colors, when put on, are entirely different from those which will appear after firing. For instance, gold is put

on in the form of a chloride which has a brown color.  

Applying a slip to a pot by Bill Gilder.