Lead is an active flux and, over the centuries, has been a very important material for potters. In recent years, safer procedures for handling and using lead have been developed. Instead of using raw lead compounds such as lead oxide and lead carbonate, potters have available frits where lead has been combined with other materials and is rendered insoluble in fritted form. That said, it is still my opinion that no responsible potter uses lead in a glaze on a pot intended to hold food or drink. While lead can be handled safely (particularly in fritted form), few potters have the necessary control or testing capabilities to assure that lead in a glaze will not leach into food or drink that the pot holds. On decorative pieces the use of lead in glazes is also controversial; however its use is more common. Some potters say they cannot get the colors they want without the use of lead. Others (and more every day) find other ways to get colors that meet their needs because, not only do they not want lead in their product, but they do not want to have to handle lead-containing glaze materials themselves. Even if the pot is sold as a decorative piece, my recommendation is that you not buy it if there is any conceivable way someone might use it for food or drink or growing edible plants at some time in the future. Be particularly careful of pottery imported from developing countries. Potters in many of the developing countries do not have the same understanding of the toxicity of lead that we do in developed countries. They sometimes use raw lead compounds and fire them to low temperatures where lead will easily release into food or drink. From my personal standpoint, I have never used lead in a glaze and never will.
Unfortunately, there is still some misleading and/or incorrect information floating around about lead and its use. To counter this, I offer the following statement of Myths and Facts in the hope we can finally bury some of this misinformation:
Myth: Using lead in fritted form makes it safe
Fact: Lead-containing frits are indeed safer for the potter to handle than the various forms of raw lead. The use of frits, however, has ABSOLUTELY NOTHING to do with the safety of the final glaze. Once the glaze is melted in the kiln, the lead no longer knows it was contained in a frit. The only things of importance from this point on are the composition of the glaze and the firing conditions.
Myth: If I use a commercial lead-containing glaze which indicates that it is food safe, it is.
Fact: This is only true if your firing conditions and things like underglazes are exactly the same as those used by the glaze manufacturer. In fact, most kilns have significant variation in temperature and your firing conditions, at least in part of your kiln, are probably significantly different from those used by the glaze manufacturer. A copper-containing underglaze may significantly affect lead release. The only way to assure that a lead-containing glaze is safe for use with foods is to have representative pots from every firing tested by a qualified laboratory. In addition FDA regulation in the United States requires that potters have a qualified laboratory periodically check their ware. Ware that might be used for food, but does not pass the leaching standards must have a hole drilled in the bottom or be permanently labeled that it is not safe for food use. California requirements are even more specific and stringent.
Myth: I only use lead-containing glazes on things like flower pots, planters and bird baths so I don't need to worry.
Fact: Lead is toxic to animals just as it is to humans. Plants raised in a lead glazed pot will absorb lead. If that pot is used for growing something like herbs the lead has just worked its way into the food chain.
Myth: I only use lead-containing glazes on my sculptural work. I don't need to worry about my functional work.
Fact: If your sculptural work and your functional work are fired in the same kiln--even at different times--you need to worry. It is well known that lead can migrate to the walls of the kiln and then contaminate future firings. Of course, if functional and non-functional pottery is fired at the same time, contamination is even more certain.
Myth: I use a lead-containing blue glaze which I have had tested and know is safe. In fact it was way below the allowable limit. I wanted to get a blue-green color so I added some copper. Because it was so far below the allowable limit in my first test, I don't need to retest it.
Fact: Addition of copper to a lead-containing glaze is widely reported in the literature to significantly increase the release of lead. COPPER SHOULD NEVER BE USED IN A LEAD-CONTAINING GLAZE.
Although lead-containing glazes have been a favorite of potters for many years and have many desirable properties, IT IS PAST TIME FOR POTTERS TO STOP USING LEAD-CONTAINING GLAZES ON FUNCTIONAL WORK. Val Cushing, an esteemed Professor Emeritus of Ceramics at Alfred University and a long time user of lead glazes, speaks for many potters when, after reviewing all the data on lead glazes he wrote in Cushing's Handbook: "It has been hard for me to accept the fact that, generally speaking, the world is a safer place if we potters eliminate lead glazes from our repertoire. Good-by lead glazes -- we shall miss you..."