Lead leaching from utilitarian ceramic ware into food and drink contained in these items has caused a number of lead poisoning cases and even fatalities over the year. This has especially been a problem with ceramic ware made with lead glazes imported from Mexico and other countries. As a result, the FDA has set standards for the amount of lead that can leach from ceramic ware used to contain food and drink. An 8-ounce cup (small hollowware), for example, must leach less than 5.0 parts/million (ppm) of lead when tested by the FDA method; large hollowware less than 2.5 ppm; and flatware less than 7.0 ppm.
This problem, however, is not limited to imported ceramic ware. Tests by the Food and Drug Administration (FDA) on domestic ceramic ware produced by craftspeople using lead glazes has also indicated excessive lead leaching. This can even be true of so-called "food-safe" lead glazes since it is difficult to have good quality control over firing conditions in kilns commonly used by craftspeople. As a result, craftspeople using lead glazes (or lead frits) should test their ware regularly to see if their glazes are safe. The ceramics industry in this country, for example, does routine testing for lead leaching in order to assure safe products.
There are laboratories which will do routine testing for craftspeople using the official FDA method. However, a recent test kit was developed by Donald and Frances Wallace of Seattle for home use, after they developed lead poisoning from Italian coffee mugs. This test kit has also received a lot of interest from potters and ceramicists who are looking for an inexpensive way to test their ware. This test kit was evaluated by the FDA and we obtained their test results.
Their conclusion was that the Wallace test kit "is capable of readily detecting lead levels of 2 ppm or more... If we consider that the purpose of a home test kit would be to alert a person to a potential hazard that will require further investigation, and not to interpret the kit as a substitute for the official procedure for leachable lead in earthenware, it can very easily accomplish its goal." In other words, this test should not be relied on as guaranteeing compliance with FDA standards, but could be used as an inexpensive, routine screening test on most pottery to determine the reliability and consistency of your firing. Pieces should occasionally be tested by the official FDA test for verification.
When using this kit, it is important to do it in a consistent manner each time and keep careful records. The FDA report also cautioned that the test releases hydrogen sulfide gas, a poisonous gas. Therefore, the test should be done outdoors, in front of a window exhaust fan, or with local exhaust ventilation (e.g. spray booth). Other metals such as copper, bismuth, and antimony can also cause a reaction.