I just got a porcelain decoration for my fish tank, but i'm not sure if it was made for a fish tank or not and i dont want it to contaminate the water.
Even fired porcelain can be quite soft, and most porcelians have no glaze on the base which will allow water to gradually seep through the porcelain. Aside from glazes not always being human or fish friendly I think the only way the porcelain can "contaminate" your tank is by raising or lowering the pH and maybe hardness of the water.