Final segment of a three-part series from the March/April 1996 issue of Clay Times
The EPA recognizes the toxicity of various metals by setting standards for them in our drinking water. There are two types of standards: 1) Maximum Contamination Levels (MCLs) which are enforceable; and 2) Drinking Water Health Advisories (HAs). The EPA standard for barium shows it is certainly not the most toxic metal we use. Potters need to consider the toxicity of many different metals. The EPA standards also can be used to interpret leach testing data from pottery. This is not a scientific approach to leach tests, but it is pragmatic in the absence of better standards. Clearly, if our pottery does not leach more metal on a 24-hour acid leach test than is allowed in drinking water, it is certainly safe for the customer to use.
|Substance||Current MCLs/HAs in milligrams/liter|
Two good labs that are familiar with this kind of testing are:
The whole problem can be avoid-ed by using glazes that employ only fluxes containing sodium, potassium, calcium, and/or magnesium combined with sources of alumina and silica. Other substances that could be used in small amounts include sources of zinc, iron, titanium, and tin. Not very exciting glazes, but certainly safe for the insides of foodware.
*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 firstname.lastname@example.org., 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 and an award-winning pot on display at the Everson Museum of Art. She is also an award-winning author of five books published on the hazards of art/ceramic materials.
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