This test is to see if a glaze is durable in an acid food environment.
It can be done with vinegar or acetic acid - my preference is to use 4% acetic acid, as this is more repeatable than variations in the acidity of different vinegars, and also corresponds to what is used in the official standards.
- Pot(s) or test tiles to be tested. You need 2 for each glaze, one to be tested and the other, with an identical clay body and glaze, to be used as the reference to compare against after the test.
- Vinegar or a 4% (by volume) solution of acetic acid
If testing tiles, a plastic container to hold the acid and test tiles
- If testing the glaze inside a bowl, pour the vinegar or acid into the bowl and cover
- If testing tiles, pour the acid or vinegar into the plastic bowl, and add the tiles glaze side up. Ensure that the tiles are fully covered. Cover
- Leave for 24 hours at room temperature
- Remove the test piece(s), rinse off in cold, fresh water and pat dry
- Compare the glaze against the reference piece. Ignore any crazing as this is likely to be due to water absorption by the pot causing expansion, rather than a chemical attack on the glaze. Use a magnifier to see more details, e.g. a magnifier app on your phone, possibly with a magnifier lens, or under a microscope.