Many potters ask me how they can determine if their glazes are food-safe. One way to be certain is to use a clear or white liner glaze inside functional pots. However, it can be safe to use coloured glazes if you keep the total amount of colouring oxides low, below around 7%.
Colouring oxides
■ Glazes can be food-safe if the weight percentage of colouring oxide in the glaze is kept low.■ For cobalt and chromium oxide, below 2%■ For copper and nickel oxide, below 3%■ Iron, manganese, vanadium up to 7%■ Mixed colouring oxides, up to a total of 7%■ Stains and opacifiers, rutile, titanium, tin, zirconium, up to 10%.■ If using carbonates instead of oxides, you can use up to 50% more. If you use only a small…
