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Whiting
calcium carbonate, lime
Chemistry
Chemistry available on new site, see link above
Significant Temperatures
- 825C: Decomposed
Links to Other Materials
- Calcium Carbonate - Related
- Lime - Related
- Wollastonite - Related
- Cache
Miscellaneous
- Family: Flux Source
- Region: North America
- Mined At: Unspecified
- Raw Mineral: No
- Generic: Yes
Notes
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.
Inexpensive non ceramic grades of whiting tend to lack the quality and consistency needed for use in glazes (especially for industrial use). Also whiting produces a very large volume of gases while decomposing, it loses more than 40% by weight. While these gases should be gone well before 1100C (and therefore should not disturb the glaze melt), in low or fast fire they can contribute to imperfections and faults in the glaze surface. With the advent of faster firing schedules in recent years whiting has been replaced by wollastonite and frits as a source of CaO in many applicatons (CaO is advantageous in fast fire because it does not lower the melting point as much as the alkalis). Since LOI is a good indicator of variation in chemistry it may be practical to do an LOI test on shipments by firing a specimen of powder in a thin bisqued bowl to confirm the consistency of dolomite shipments.
There are many alternate no-LOI sources of CaO (e.g. wollastonite, frits) and incorporating one of them to source the CaO instead is a classic application of ceramic chemistry calculations.
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 (causes glazes to craze).
Properties
Glaze Opacifier - White
High calcium coupled with lower alumina will favour the formation of calcium silicate crystals during cooling. This mechanism promotes opacity.
Data
- Specific Gravity: 2.72-2.92
- Specific Gravity: 2.72-2.92
Suppliers
- Generic
Authors
- Tony Hansen (Owner)
XML
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