Barium carbonate is popular for the production of crystal/matte glazes. Barium carbonate is commonly added to clay bodies in small amounts (0.2-0.8%) to halt fired surface scumming normally found in red clays. Barium carbonate produces gases as it decomposes and these can sometimes cause pinholes in glazes. Glazes containing barium in higher concentrations are normally considered not safe for food or drink.