Weather Resistant - Firing temperature: 1200-1250 degrees F. Vitreous paint is a mixture of ground glass and a pigment oxide. These superior glass stains and paints from Reusche are offered in 1 oz. (28.3 g) packets, containing powdered colors which must be mixed with water and gum arabic or other mixing agents before application to glass and subsequent kiln firing. 1 oz. covers 300 square inches.These are basic paints for painting on glass. Not bright transparent stains. Opaque colors are limited to blacks, browns, flesh, red and grey-greens.