Product detail

ZnO (99.80% ZnO) It can be an active flux in smaller amounts. It generally promotes crystalline effects and matteness/softness in greater amounts. If too much is used the glaze surface can become dry and the heavily crystalline surface can present problems with cutlery marking. Other surface defects like pitting, pinholing, blistering and crawling can also occur (because its fine particle size contributes to glaze shrinkage during drying and it pulls the glaze together during fusion). Calcined zinc oxides are available and apparently produce less glaze surface defect problems. You can calcine zinc on your own in a bisque kiln, fire it at around 815C. Calcining a mix of zinc and kaolin produces a more workable powder. However calcined zinc tends to rehydrate from atmospheric water (and get lumpy in the process). Zinc oxide sublimes at 1800C but it reduces to Zn metal in reduction firing and then boils at around 900C (either causing glaze defects or volatilizing into the atmosphere). Note that electric kilns with poor ventilation often have local reduction. While it might seem that zinc would not be useful in reduction glazes, when zincless and zinc containing glazes are compared it is often clear that there is an effect (e.g. earlier melting). Thus some zinc has either remained or it has acted as a catalyst. The use of zinc in glazes is limited by its price, its hostility to the development of certain colors and its tendency to make glazes more leachable in acids (although zinc itself is not considered a hazardous substance). Source: Digital Fire.