Magnesium Carbonate Fine Powder (Magnesia)

Magnesium carbonate (MgCO3), also sold as light mag carb or magnesia, is a very fine, fluffy white powder at lab grade, typically 99 percent or better. It is the usual source of MgO in glaze work, acting as a matting agent that gives smooth, buttery matte surfaces at mid to high fire and as a refractory opacifier that produces bright white mattes in lower-fire glazes.

Its fineness and high dry shrinkage also make it the standard addition for deliberate crawling and snakeskin textures. Elsewhere it is used as a drying agent, a filler, and an antacid ingredient.