- As prepared bodies are made from naturally occurring clays they are inevitably subject to small variations from batch to batch. To take this into account, customers are advised to test the clay from a new batch on a small scale before putting it to full use.
- A glazed ceramic product can be achieved by a number of different firing routines, the commonest of which are:
- Twice-firing: In this procedure the dried clay pot is first heated to a temperature above 1000°C – the biscuit fire. Then the glaze is applied and the piece is fired again to the glaze/body maturing range.
- Once-firing: In this procedure glaze is applied to the unfired pot and then, in one firing cycle,the glaze and body are matured together. This process does require test work by the user as problems can arise. The gases in the greenware must be expelled; if there is glaze covering the entire pot the escaping gas can easily cause pin holing in the glaze finish.