Kaolin is the purest clay that nature offers, one TLV (threshold limit value) quoted for it is 2.0 milligrams per cubic meter of air breathed (primarily because of the potential of associated quartz). By comparison, iron oxide is considered a safe-to-use material at 5.0, tin oxide is 2.0, barium carbonate is 0.5, quartz is 0.1-0.05.
Some books cite the presence of some free silica in kaolin as a silicosis hazard; however, other sources and regulatory bodies recognize no known hazards and consider it a nuisance dust (quartz often less than 1%). Ball clays, on the other hand, can have a much higher quartz content. That being said, the grains are often round rather than angular.
Like many clays, data sheets often caution against slipping on a slippery aqueous suspension if it gets spilled on the floor!
ALLERGIES: Clays are composed of tiny particles of inert minerals (thus insoluble). Some clays are relatively homogeneous (all the particles are the same) and some are composites (containing particles of many minerals). Molds, mildews, and other organisms can make their home in clay, along with their byproducts, and thus cause reactions. Sedimentary clays can contain calcium and magnesium sulfates, these are at least partially soluble and there is thus a possibility of allergy (however sulfates are common additives to many household products are not considered hazardous).
|By Tony Hansen
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The purest of all clays in nature. Kaolins are used in porcelains and stonewares to impart whiteness, in glazes to supply Al2O3 and to suspend slurries.
Ceramic glazes and clay bodies can host micro organisms. They can be just a nuisance, a source of worry or can render a product useless. What should you do?