Over-glaze colored ceramics are products made by pasting colored paper made of over-glaze colored ceramic pigments on the glaze or directly coating the surface of products with pigments, and then firing at 700~850℃. Because the firing temperature can't reach the melting temperature of the glaze layer, the flower surface can't sink into the glaze and can only cling to the surface of the glaze layer. If you touch it by hand, the surface of the product has a concave-convex feeling, which is uneven to the naked eye.
The firing temperature of ceramic color in glaze is higher than that of glaze color, reaching the melting temperature of glaze. When the glaze melts, the ceramic pigment sinks into the glaze and is covered by the glaze layer after cooling. Touching the surface of the product by hand is as smooth as glass, and there is no obvious concave-convex feeling.
Under-glaze colored ceramics is a traditional decoration method in China. All the color decoration of the product is carried out on the porcelain blank, and it is fired at a high temperature after glazing. Like the color in glaze, the surface of this product is bright and smooth, and there is no uneven feeling.
In glazed porcelain, a high-temperature colorant is added to the ceramic glaze to make the glazed surface of the fired product show a certain color, such as yellow, blue and bean blue.
White porcelain usually refers to ceramics without any color decoration, and the sales volume of this product in the market is generally small.
The above different decoration methods, in addition to showing their own artistic effects, mainly differ in the content of heavy metal elements such as lead and cadmium. Among them, the contents of lead and cadmium in glaze, underglaze and most glazed porcelain and white porcelain are very low, while in glaze, if inferior pigments are used in the processing of ceramic decals, or the amount of pigments with high lead and cadmium is too large in the design of decals, or the temperature and ventilation conditions are insufficient during firing, due to the use of lead-containing frit glaze,
Lead and cadmium dissolution is a safety and health index related to human health. The content of lead and cadmium in human blood should be as little as possible. If people eat food with high lead and cadmium content for a long time, it will lead to the deposition of lead in the blood, leading to the damage of central nervous system, kidneys and other organs. It will have a serious impact on children's intellectual development.