Underglaze colors, also hot-fire colors (French: décor sur émail cru ) are colors for painting ceramics , especially faience and porcelain , but also earthenware , which, unlike on- glaze colors , are applied before smooth or sharp firing. They can be applied directly to the body before glazing - as in the case of porcelain - or, despite the name, immediately afterwards on the glaze - as in the case of faience. In both cases, the decoration is sealed and protected by the glaze.
The spectrum of underglaze colors is much smaller than that of onglaze colors because only a few dyes - all of them metal oxides - can withstand the very high temperatures (1300–1410 ° C) of the glaze. Initially, only cobalt blue was known as an underglaze color, but the color tone could be varied slightly by adding alkaline additives to the glaze (light, dark, green blue). By the last decade of the 17th century, a three-tone color palette was reached, from cobalt blue to manganese violet to antimony yellow. In the course of the 18th century, technical innovations from southern Europe and Asia added copper green and iron red to the range.
The chemical industry has made it possible to produce other colors since the 19th century. In 1807 green, black and brown in the form of chromium oxides were developed, and at the end of the 19th century yellow-red and yellow-brown tones were developed from compounds of tungsten , molybdenum , titanium and vanadium . This exhausts the spectrum of underglaze colors.
- Porcelain paint
- Cobalt blue
- Copper green
- Chrome green
- Antimony yellow
- Manganese Violet
- Manganese brown
- Gustav Weiß: Ullstein porcelain book. A history of style and technology of porcelain with a list of brands . Ullstein, Frankfurt / Main 1964.
- Sandy Alami: "» Of truly artistic execution «. Porcelain plate painting from Thuringia since the 19th century. Studies in folklore in Thuringia", Volume 5, Münster / New York 2014.