What happens to clay in glaze firing process?

Do you want to know how the clay is transformed during the glaze firing process? The answer is here.

• Step 1 dryingThe first firing to 120 Celsius is a drying period. The water is evaporated from the body and the glaze.
• Step 2 ceramic change and decomposition The clay is composed of raw minerals which is converted to oxides at 350-573 Celsius. Silicate is expanded for 3 times at this temperature. Therefore, slow firing is required to avoid crack.
• Step 3 dunting This occurs at 573-600 Celsius. A temperature rise which is too rapid could create a large temperature difference across a pot causing a stress which results in a crack.
• Step 4 fusion starts with sodium and potassium oxides.
• Fusion starts at 600 Celsius and melts with Aluminium silicate and become crystalized.
• Step 5 vitrification continues Up to the biscuit temperature, the body is unchanged.
• The glaze fluxes start their action at different temperatures and therefore, as the temperature rises, more fluxes become involved in active fusion.

The glaze is melted at the same temperature as the body. Particularly sodium and potassium found in feldspar react with calcium oxides, zinc oxides, barium oxides and magnesium oxides. They are then melted with Alumino silicate and result in the formation of crystals.