Food safety is determined by a number of factors: glaze and clay maturity; glaze melt; glaze fit; and solubility or stability of fired glaze materials. Non-food-safe glazes are so designated because they are either unstable in the fired state and may leach metal oxides into foods, especially acidic foods/liquids; or have a crazed glaze surface where bacteria can become lodged and grow.
All cone 10 gloss glazes at CAW meet the definition of food safe as long as they remain uncrazed; that is, our glossy glazes are chemically stable and contain no lead or other highly toxic, soluble materials. See Glaze Stability .
Matt glazes, however, are not recommended for use on surfaces that will come into contact with foods because their mattness is achieved essentially by underfiring, which can leave them unstable.