It is probably ok. But one test I know is you put a vinegar in it, and let it sit over night. Once you pour it out and clean it, if there isn't a color change where the liquid was it is ok. If there is a slight change in color, I wouldn't use it.
My ceramics professor used a dish that she thought was safe and had some type of dressing in it during a party. She left it sit overnight and went to wash it the next morning and she noticed that the color of the glaze was slightly lighter where the dressing was. It had leached. No huge effects on humans for a one time use, but not something you want to be using for foods (or a fish).
Last edited by MoePaac; 06-24-2010 at 07:54 AM.