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Whiting has traditionally been a source of CaO in raw glazes and glass (however whitings also typically contain some dolomite as a contaminant). Whiting is generally inexpensive and there is a large calcium carbonate industry worldwide for non-ceramic uses of this mineral. Well known deposits are the chalk cliffs of England, France and Belgium. Marble and calcite ores are abundant in many places.
In low-fire bodies, calcium carbonate is sometimes added in small amounts as a filler to reduce fired shrinkage and act as a whitener. It is also common to see 5% whiting included in porous earthenware body recipes to prevent moisture expansion (which causes glazes to craze).