When the whole design has been pierced, moisten the finger with water and soften the edges of the decoration, that the glaze may flow freely over it. Decorations in high relief are made as follows: Small lumps of clay, as nearly as possible the consistency of the piece of pottery, are applied to the portions which are to be decorated, and which have previously been criss-crossed with a steel tool, and wet with slip. The design is then moulded with the hands and wooden modelling tools, working the edges close on to the surface of the piece.
The Glaze and How to Apply It
CHAPTER V
THE GLAZE AND HOW TO APPLY IT
Clay that is simply baked, without a glazed coating, will not hold water perfectly.
One can imagine what a blow it must have been to the early potter when he found that this was the case. Some say that he used wax at first to close the pores of his pottery, and later—perhaps by the overheating of a kiln—glazed pottery was discovered. Pottery that is soft will develop a semi-glazed surface when overfired, and it is probable that some such accident suggested the use of the glaze.
The first glaze was doubtless a pure silicate of soda. Oxide of lead added to this made it more fusible, but it was not as hard or durable.