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Barium Glazes: How Safe?

By Monona Rossol

Part one of a three-part Series on barium from the December 1995 issue of Clay Times

Barium glazes do not present an unreasonable hazard to potters as long as they understand barium's health effects, use local ventilation (a spray booth or other area in which powdered materials can be handled safely), wear protective equipment, and practice good hygiene. Potters with heart or blood pressure problems should be especially careful because barium can worsen these conditions.

The risk during use of glazes is primarily from inhalation of tiny amounts of the dust. Inhalation of insoluble barium sulfate is only roughly as hazardous as inhaling iron oxide. On the other hand, slightly soluble barium carbonate is far more toxic. Still, standards for exposure to barium carbonate dust are less restrictive than those even for free silica.

All this is easier to understand if we look at a table of workplace air quality standards (Threshold Limit Values/TLVs) for various metals and their compounds. In general, the smaller the TLV, the less is allowed in the workplace air, and the more toxic the material is to inhale.

Inhaling barium compounds during glazing is far different from ingesting small amounts of barium with your food. For this reason, barium glazes should not be used for food wares unless they have been tested to assure that they will not contaminate consumers' food.

Metal compounds in order of
increasingly restrictive TLVs*
TLV in milligrams/cubic meter (mg/m3)
Calcium, magnesium, aluminum 10.0
Barium sulfate (insoluble), iron oxide 5.0
Fluorides (e.g. cryolite, fluorspar) 2.5
Tin, kaolin 2.0
Copper, nickel 1.0
Barium carbonate (soluble), antimony 0.5
Manganese, cobalt, selenium 0.2
Silica (quartz/flint) 0.1
Silica (cristobalite or fired quartz), lead 0.05
Arsenic 0.01
Cadmium, beryllium 0.002

*Material adapted from the data sheet: "Ceramic Ware Hazards", ACTS, M. Rossol, 1993. Available for $1.50 from ACTS at (212) 777-0062 or e-mail 75054.2542@compuserve.com., this 6-pg. technical data sheet also includes FDA labeling rules for decorative ware that looks like it could be used for food.

Monona Rossol is an industrial hygienist/ chemist with an MFA in ceramics/glass, an award-winning pot at the Everson Museum of Art, and has written five books on the hazards of art/ceramic materials.

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