Research update: UC offers lead test around state
California Agriculture 48(7):9-9.
Published December 01, 1994
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For the past few years, UC Cooperative Extension offices around the state have been offering what they call the “UC Quick Lead Test,” a 20-minute test which can determine whether a piece of pottery or ceramic ware is leaching lead.
Many pottery glazes contain lead, which adds color, texture and luster. When properly fired — or heated to a high enough temperature for a long enough time — the metals become incorporated into the glaze and are resistant to acid leaching.
But some pottery isn't properly prepared or fired. Glazes that are cracked or worn can also cause leaching of lead when they come into contact with acidic foods, such as tomatoes, according to UC Home Economist Shirley Peterson.
In 1991, concerned about the health effects of lead, the U.S. Food and Drug Administration (FDA) issued new guidelines concerning pottery and ceramics manufactured in, or imported to, the United States. Pottery made in the United States, or foreign pottery imported through FDA-approved channels, are screened for leachable lead. Not all pottery or ceramics manufactured in foreign countries meet FDA standards. Tourists and military may bring home dishware from foreign countries, which are not subjected to the screening process, but may contain leachable lead. Lead can also be found in antiques.
The UC lead test, which is adapted from an FDA test, uses a mixture of citric acid, “about as strong as lemonade,” which is placed on all colors in the pottery that come into contact with food, Peterson said. After standing for 20 minutes, some of this citric acid is transferred to filter paper, where it is tested with rhodizonic acid, which turns from goldenrod to pink on contact with lead. The darker the pink, the more lead is there.
Cooperative Extension originally offered the test at a Davis farmers' market and the Sacramento County Extension Office. Of 92 pieces tested, they found more than 6% leached lead, many of them pieces from Mexico, in which the glaze had been poorly or incompletely applied, and the pieces gave a “thunk” when tapped, which is indicative of ceramic ware fired at a low temperature.
Peterson said the lead tests are available at many of the Cooperative Extension offices. In addition, they can be obtained commercially for people who are concerned about the safety of their ceramic ware.