Under-glaze colors. For under-glaze decorations, kaolin, quartz, white broken ceramics and other silicate basic components are combined with heat-resistant color pigments, e.g. B. vanadium(III) oxide V2O3, chromium(III) oxide Cr2O3, manganese(IV) oxide MnO2, iron(III) oxide Fe2O3, cobalt(II) oxide CoO, nickel(II) oxide NiO and Mixed oxides (spinels), finely ground or impregnated with metal salt solutions (gold chloride, rare earth metal chlorides) and annealed at 900 to 1400 C. The color tone is developed with the glaze components via dissolving and reaction processes.
Over-glaze colors (enamel colors, enamel colors). For the low-melting on-glaze decoration, the color oxides are ground with alkali metal and lead borosilicate glasses, which enable good melting into the hard glaze.
The color material of the over-glaze color is the glazed surface of the porcelain that has been fired, and there are various patterns on it, while the color material of the under-glaze is a blank that is formed and dried, and various patterns are painted on it.
Over-glaze colors require two firings, while under-glaze colors require one firing.
The surface of the over-glaze color is smooth, non-fading, and durable, while the pattern drawn by the under-glaze color highlights the glaze surface and feels more hand-feeling, and is not as smooth as the under-glaze color.
The under-glaze color is quick-matched with raw embryos after baking, the upper cells are decorated with colored paintings, and then glazed, while the over-glaze color is fired on the white porcelain body, decorated with colored paintings on the surface of the porcelain, and then fired in the kiln , the painted pattern and glaze color need to be fired separately.
The under-glaze color material is fired at high temperature, and the color change is difficult to grasp.