During this process, which is also called sintering of engineering ceramics, the dried molded body is converted into a hard and waterproof product. At temperatures of up to 1,000 °C the individual elements such as water, organic auxiliaries and carbon dioxide evaporate. The clay constituents decompose, and new minerals are formed. The crystals bond onto the grain boundaries and are merged due to the glass elements. The material properties of the baked material are decisively defined by the mass and type, i.e. the grain size distribution or the textures of the crystal and glass phases as well as by the fraction and structure of the pores.
Ceramic firing takes place at temperatures up to approx. 1,400 °C. The different raw materials, with a view to the product to be achieved, often require the temperatures to be individually adjusted (temperature profile). Furthermore, this firing process must occasionally be carried out under a reducing atmosphere in order to avoid possible yellow coloring in white tableware or sanitary ceramics caused by iron contamination.
In mass production, periodic and continuous furnaces are usually used, e.g. pottery kilns or chamber furnaces, which are operated with fossil fuels, while in craft businesses electrical furnaces tend to be used. Kilns for handling small quantities are often available as open systems, whereby the fuel gases come into direct contact with the kiln charge, as well as muffle furnaces, whereby the fuel gases heat the charge indirectly.