Clays For Vitreous Enamels

Vitreous enamels are similar in composition to ceramic glazes in the sense that they are both glasses with random structures which give rather indefinite lines in X-ray spectra & hence, it is uncertain what compounds are present, except that they are complex silicates & borates. While ceramic glazes can be fired for several hours, since the substrate is stable to heating, enamels must be fired in a matter of minutes to avoid excessive oxidation of the base metal & warping. This means that numerous chemical reactions between raw materials in the enamel must have been carried out in the pre-firing or fritting operation, whereas with ceramics these can often be allowed to proceed in the actual glost fire.