- Between Ambient -- 200°F: Physical water evaporation.
- From 400°F -- 1500°F: Organic material, such as paint, wax, and oils, is burned off. This process often produces smoke, hence why ventilation is important.
- About 660°F: Chemical water evaporation. Chemical water is part of the clay's molecular structure. Losing this chemical water marks a permanent change in the clay; it moves from clay to ceramic. Once this change occurs, the object can no longer be recycled by simply adding water.
- Above 1500°F: Sintering. Sintering is the fusing of particles under extreme heat (and/or pressure). The particles do not melt but fuse, making the ceramic harder and more compact. Your object will shrink during this process, and the shrinkage depends on the clay.
- Between 1500°F -- 1971°F (Cone 04): Porosity development. Before complete vitrification, there is a sweet spot where the ceramic has sintered but is still porous. This allows the glaze to penetrate the surface and adhere well during subsequent glaze firing.
- Between 500°F and 1500°F: Gasses escape from the glaze.
- Between 1800°F and 2300°F:
- The glaze melts, transforming from a powdery coating to a glass-like surface. The exact temperature depends on the Glaze.
- Chemical Reactions: Various reactions within the glaze take place. This includes the melting of silica, metal oxides, and fluxes.
- Interface Reactions: The glaze interacts chemically with the ceramic body, significantly affecting the glaze color.
- 1940°F to 2269°F: Vitrification of the Clay Body. The clay body undergoes its final vitrification. This turns its molecules from a porous structure to a glass-like structure. Higher temperatures make for a more complete vitrification. (We allow our kilns to be fired to Cone 6!)
- Cooling:
- Molten glaze solidifies: Crystallization may occur, affecting the appearance of some glazes. Controlled cooling can impact the crystal formation and, therefore, the appearance of the glaze.
- Shrinkage: Both the glaze and the ceramic shrink as they cool. The shrinkage is (almost always) at a different rate, which can cause cracks in the glaze (called crazing).