Are the glazes you’re using food safe?

Anthea Grob

Gorgeous, but does that glaze you drool over belong on a pot for food and drink?

It is so, sooo easy, to get caught out. You drool about that glaze in the picture, imagine it all over your pot, click ‘buy now’, and relinquish your credit card details. Before you know it, the glaze powder arrives. Great; you make it up, stick it in the firing and drool over it when it comes out of the kiln because it really looks so fabulous. You are still in the glow of that rare successful outcome when someone absolutely rains on your parade by asking “Is that glaze really safe?” So you go searching the fine print and find that likely, it isn’t!

I recently purchased a glaze from a Kiwi provider over the internet that contained Barium which is not food safe. I did this quite accidentally because nowhere near the point of purchase did it say “DO NOT USE FOR FOOD POTTERY” or show any other kind of warning. I felt foolish because, with my knowledge of glazes, I should have guessed it was likely to be the case. It was expensive so I made it up, alerting students to use it on pots or pot surfaces that would not come into contact with food or drink—(coffee, for example, is about 4.5 percent acid). This has prompted me to alert other members to the risks. Many websites, both Kiwi and others, do not show the safety information anywhere near the point of sale.

Furthermore, many of the glazes sold as “in our opinion safe for food surfaces” are not in fact tested, nor are the ingredients, such as lead, identified. Just because it does not say that the glaze contains lead does not mean it is not present.

I know it is a pain, it might ruin the look you are going for (and we all know that butting up the inside-glaze and outside-glaze is a bit of an art that can wrong) however please choose a glaze suitable to be a ‘liner’ glaze. These are usually clear or white (or containing iron as the colourant). Unless you are satisfied about the glaze ingredients, choose a balanced glaze (properly fired) for the surfaces that come into contact with food and drink. Be aware that colourants added to a safe glaze can alter its safety through leaching. If you have used a glaze you are worried about, test it with vinegar or, slightly more acidic, lemon juice.

To learn more I would suggest John Hesselberth’s website or his book (in the WPA library) Mastering Cone 6 Glazes. One test he recommends is to simply put a lemon slice on a glazed plate overnight and look for changes in gloss or colour. Tony Hansen ( also suggests… “Since bases (e.g. detergents) can also leach glazes, (not just acids) another interesting test is to leave one of two identical pieces of ware in your dishwasher for a few months and then compare them for differences in surface quality.”

We are trying for a safety culture at WPA and need ourselves, our friends and our customers to be safe. So, yes, we may need to rain on our friends or our own parades; we may need to forgo the matte black on a plate despite how “now” it is and do look for the safety information when buying glazes on the internet but do not assume it will be there.