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Common Sense About Barium Leaching

By Monona Rossol

Part two of a three-part series on barium from the January 1996 issue of Clay Times

I'm old enough to remember that the tests for leaching of barium in the '70s and '80s were done primarily to settle an argument. Some potters insisted that high fired glazes don't leach. Since barium was a common toxic flux for high fired glazes, barium glazes were tested. The tests showed that high firing does not necessarily create a "stable" glaze.

We need to understand that when we fire clays, glaze chemicals, or make glass, we are doing what only Mother Nature used to do­create new minerals, rocks, and obsidians. And like these naturally created geological substances, the "rocks" we create also begin to "weather" as soon as they are made.

All glazes and glass are slowly dissolving. Water, acids, and (for some glazes) alkaline environments speed the process. What we strive for are glazes that dissolve so slowly that released metals are barely detectable in a 24-hour FDA acid leach test. While there are no FDA standards for metals other than lead and cadmium, clearly the other metals can be harmful, too. We now know that there are toxic thresholds for all metals­even iron and calcium. The thresholds vary with the toxicity of each individual metal.

To know when we are overexposed, we have to look at our entire dietary intake, the quality of our water, sources in our homes and workplaces, plus additional exposure from ceramics. We may even have to look at our medications. If one of our customers is taking lithium to control depression, it doesn't take much additional lithium from a coffee cup to create a problem. We owe our customers glazes that do not leach toxic metals of any kind into their food.

*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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