When it comes to food safety in ceramic ware, many designers take great care to ensure that the glazes they are using are not leachable. However some don't believe it's a big issue that should be taken quite seriously. If you're making functional ceramic ware then the safety of your product should be important. As artists and designers it's our responsibility to ensure that its safe for its intended use, especially if it involves food.
So why is it such a big deal?
If you are making functional ware you want it to be safe for the consumer. The glaze should be hardy and free from any toxic chemicals that may leach into the food or drink. The glaze needs to be able to withstand washing, and so you want it be able to resist degradation from detergents. And some surfaces need to be able to resist abrasion from the use of metals utensils like knives and forks. As a designer you want to solve problems and make objects that better the consumers experience. Hence ensuring that the glazes you use are hardy and food safe should be a priority.
If you're mixing your own recipes...
If you like to mix your own glazes, like I do, you need to be aware of what chemicals are in your glaze and if they're food safe. Barium and lithium for example, are known to be toxic (as is lead). So... just don't use them, find alternatives or change the recipe you're using. It's also good practice to ensure that your glaze is balanced, as glazes are leachable if they contain inadequate glass former and alumina. Also be wary that the glaze has the right amount of melt, and look out for crazing (cracks). Crazed glass is notorious for harbouring bacteria. Its always good to do a few at home tests to check for their safety, as well as send samples off to have professionals test them for their safety. Always get them retested if you change anything about the recipe also.
If you purchase glazes...
Always read the label, and if the company hasn't explicitly stated if its safe then ask them. Most commercial glazes in Australia are food safe these days, and will have warnings if they're not. But it's always good to not assume and double check if your going to be using the glaze for your dinnerware. You don't want a consumer to come back to you in a couple of months with complaints or concerns! So just be wary, and ask if you're not sure.
An at home test you can do...
One of the quickest and easiest tests you can do is to half fill a vessel with vinegar and let it sit for 24 hours. Empty and let it dry, then have a look. If the colour or texture of the glaze that was in contact with the vinegar has changed at all in that time, its not stable and don't use it for any surfaces that will be in contact with food. Its likely that it will leach when in contact with acidic foods and it won't be resistant to washing detergents. If your glaze hasn't changed though send it to professionals and have it checked over, just to be sure. There are other at home tests that also work, and it's a good idea to try a few to see how the glaze reacts to different acids.
So in short, its good practice to always test your glazes. If they're not safe, don't use them for functional ware and if they pass at home tests, send them to professionals to be sure. Happy glazing!