Disclaimer and Health Warning
Glazy takes no responsibility for the recipes in this database. You should be aware of the dangers of ceramics materials when mixing, applying, and firing glazes.
Ceramic recipes "do not travel well" and are very sensitive to differences in materials, preparation (seiving and ball milling), application, firing, and cooling. Even for well-known and well-tested glazes, your results may be significantly different from others. Therefore,knowledge of how to test and adjust glazes is extremely important.
Recipes in this database contain dangerous chemicals that can injure or even kill you through short-term and long-term exposure when ingested, inhaled, or absorbed through the skin.
Mixing & Firing Hazards
When preparing, mixing, and firing ceramic materials you must take the proper precautions as mandated by local and national regulations. A respirator must be worn at all times when handling dry materials.
Toxicity & Food Safety
Some ceramic recipes may be toxic even after firing, leaching toxic materials into food or drink. It is your responsibility to insure that functional ware meets all criteria for safety as mandated by local and national regulations.
Toxicity and food safety is a complicated issue that depends upon a number of factors, including the toxicity of ingredients, glaze durability and flaws, leaching, and how well a glaze is fired from kiln to kiln. To make the situation even more problematic, government regulations differ by country and region.
Given these variables, no one on Glazy can tell you with absolute certainty whether or not a specific glaze is "food-safe". Glazy itself makes no claim and accepts no liability as to the food safety or toxicity of recipes listed on the glazy.org website. The only way for you to know with absolute certainty if your glaze is safe is to a) do not include any regulated metals like lead & cadmium or b) have your glaze tested by a certified lab.
If you are making functional ware, it is your responsibility to educate yourself as much as possible and to ensure that you do not harm your customers.
The best way to avoid issues of glaze toxicity and leaching is to use a "liner" glaze. A liner glaze is a clear or white glaze applied to all areas of food contact (for example the inside & lip of bowls, cups, and plates).
There are a number of glaze books and classes that can teach you guidelines and ways to test for toxicity. Listed below are a few online articles:
Copper Leaching and Glaze Durability by Peter Berg and Matt Katz
An Overview of Glaze and Glazing Safety by William M. Carty and Hyojin Lee
NCECA Presentation: An Overview of Glaze and Glazing Safety by William M. Carty and Hyojin Lee
Glaze Stability and Food Safety by Sherman Hall
Two Tests to Determine if Your Glaze is a Food Safe Ceramic Glaze by Gabriel Kline
Are Your Glazes Food Safe or are They Leachable? by Tony Hansen
Food Safe by Tony Hansen
Hazards in Ceramics by Marvin Bartel
Safety and Hazards in Ceramics from Princeton University Environmental Health and Safety
Technical information for potters by Tim Thornton