According to a process patented in Germany, a mixture is prepared from various natural or artificial varieties of ocher, to which 25-50 per cent of finely powdered more or less metalliferous or sulphurous coal is added. The mass treated in this manner is brought together in saggars with finely divided organic substances, such as sawdust, shavings, wood-wool, cut straw, etc., and subjected to feeble red heat. After the heating the material is taken out. The glazings now exhibit that thin but stable metallic color which is governed by the substances used. Besides coal, salts and oxides of silver, cobalt, cadmium, chrome iron, nickel, manganese, copper, or zinc may be employed. The color-giving layer is removed by washing or brushing, while the desired color is burned in and remains. In this manner handsome shades can be produced.