First firing "the BISCUIT"

This term is used to indicate an object modelled with clay and baked the first time at a temperature oscillating between 980°C and 1000°C. Before the clay objects are inserted into the oven for the first baking, they must be completely dry so as to avoid breaking during baking. The pieces are placed on shelves of refractory material, which are supported by small columns. During the first baking the objects in the oven may even touch each other, but this must be absolutely avoided when they are enamelled, because the melting of the enamel may cause the objects to stick together.
The features of a high-quality biscuit are: rosy, lightness and sonority. If the colour is dark and the sound is dull it means that the biscuit is not well baked; if the colour is yellow-green or greenish it indicates an excessive baking and the objects will probably present a deformed aspect, because the clay is melting.
In the second case, the biscuit would have little absorbance and it would not absorb the necessary quantities of enamel during the enamelling phase.
The baking temperature is checked through suitable pyrometers, which precisely indicate the degrees inside the baking chamber; in ancient times it was customary to use biscuit specimens covered with enamel which were extracted while checking the melting, or else the temperature was controlled according to the colour inside the oven. This control was carried out through specially provided lights.
The temperature check is accomplished also through cones which are composed of a mixture of clays and melting materials called pyroscopic cones, i.e. a pyramidal element which is about 5 cm high, that softens and bends when the oven reaches the melting temperature, thus warning us that we are approaching the desired temperature.