While BaCO2 has a high melting temperature, it will break down much readily in a glaze melt (liberating the BaO for glass building). It decomposes even more readily during glaze melting in a reduction atmospheres. The dissolution process happen most quickly if BaCO3 is present in small amounts (e.g. 5% or less). Even if present in larger amounts, the glaze matrix can solidify with both types, one participating in the glass microstructure and the other acting as a refractory filler, opacifier and matting agent (especially in low temperature glazes). Effects produced when baria is acting as a filler are sometimes mistaken for those of a true baria crystal matte. Such will likely leach toxic BaO