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Sodium, potassium, magnesium sulfates can be found in many clays. These are soluble and often dealt with by the addition of barium carbonate to precipitate them. However, while the reaction that occurs produces insoluble chlorides of sodium, potassium, magnesium, these can have their own issues (eg. firing them generates of gases and fumes harmful to kiln refractories). Heavy clay industries can tolerate clays with higher sulfate contents, but other industries, such as tile, need lower contents).
Out Bound Links
Organic Matter in Clays: Detailed Overview
A detailed look at what materials contain organics, what its effects are in firing (e.g. black core), what to do to deal with the problem and how to measure the amount of organics in a clay material.
In ceramics, when we speak of deflocculation, we are almost always talking about making a casting slip. Glazes can also be deflocculated (to reduce water content and densify laydown).
Deflocculation is the process of making a clay slurry that would otherwise be very thick and gooey into a thin po...
Barium Carbonate - BaCO3
Barium Carb, Witherite
The Use of Barium in Clay Bodies
Hazards of barium carbonate, considerations regarding its use in clay bodies for precipitation of soluble salts
By Tony Hansen