Whiting / Calcium Carbonate

Calcium Carbonate (CaCO3), commonly called Whiting in the ceramics trade, is a highly refined calcium source that behaves identically to limestone in firing but offers greater purity, finer particle size, and more consistent results.

Where natural limestone can contain traces of iron, silica, and other impurities that cause slight color variations, whiting is chemically precipitated or finely ground from pure marble or chalk sources, producing a bright white powder with reliable chemistry batch after batch. For bright white glazes, celadon bases, and any recipe where predictability matters, whiting is preferred over limestone.

Functionally, both materials release carbon dioxide at around 825 degrees Celsius during firing, leaving behind calcium oxide (CaO) as the active flux. CaO is the workhorse flux of all high-fire stoneware and porcelain glazes, producing hard, durable, food-safe surfaces at cone 9 to 10.

The ceramics tradition of using whiting dates back centuries, with Song Dynasty potters using ground marble as the key flux in their celebrated celadon glazes. European potters picked up the practice in the Renaissance for majolica and faience production.

Typical usage: 10 to 25 percent in cone 9 to 10 glazes as the primary flux. 5 to 15 percent in mid-fire glazes. 2 to 5 percent in clay bodies as a whitener and flux.

Difference from Limestone: Chemically identical (both CaCO3), but whiting is purer, finer, and whiter. Use whiting for bright glazes and precise recipes; limestone works for standard functional pottery where small variations don’t matter.