COLORS - Double firing in pottery
Colors, double firing: colors that are going to be fired two or three times, at the same or at a lower temperature, should be tested to see if they can be affected. The higher the temperature for verification, the more likely it is for a change to occur. They can lose their shine, become darker and suffer other alterations. If using colors that vitrify at different temperatures, you must always start with the highest temperature that the clay can take and then move downwards as over firing can damage the clay and change and burn colors away. Stoneware can be fired up to 1300º C and then decorated using and mixing different methods, first with earth pigments and oxides, which vitrify at 1280º C, then with oxide at 1000º C, then Majolica method at 980º C and then porcelain at 800º C.