Zinc Oxide

Zinc oxide (ZnO) is a common material used in ceramics, especially in glazes, due to its versatile properties. Here's a detailed summary, including safety considerations:

Role of Zinc Oxide in Ceramics:

1. Glaze Flux: Zinc oxide functions as a flux, helping to lower the melting temperature of glazes. It promotes smooth, glossy finishes and can produce various textures based on firing conditions.
2. Colorant Interaction: Zinc oxide influences the colors of other metal oxides in the glaze. For example, it can enhance the development of iron oxide browns or influence the depth of cobalt blues.
3. Opacifier: ZnO can act as a mild opacifier, adding a soft, creamy appearance to glazes. It’s often used in matte and satin finishes.
4. Surface Effects: In some formulations, zinc oxide contributes to crystalline effects, especially when used in controlled cooling processes to produce zinc silicate crystals.

Safety Considerations:

1. Handling Zinc Oxide: Like many ceramic materials, zinc oxide should be handled with care. In powder form, it can be an irritant if inhaled or if it comes into contact with the skin. When working with zinc oxide, wearing protective gear such as a dust mask, gloves, and goggles is recommended.
2. Food Safety in Glazes: Zinc oxide is generally considered safe for use in glazes on food-contact surfaces if properly fired. However, it is important to ensure that the glaze matures fully and that the zinc oxide is fully incorporated into the glaze matrix to prevent any potential leaching.
3. Firing Stability: Proper firing is crucial when using zinc oxide in glazes, especially in functional ceramics. Underfiring can lead to incomplete reactions, which might affect both the durability and the safety of the glaze. Zinc oxide is most stable when fired in oxidation atmospheres at temperatures between cone 6 and cone 10.