I want to make some caves/hideout spots for my fresh-water aquarium fish, but first I need to know if these pieces could be toxic to my fish. I will be using high-fire glaze and I plan to make sure every part of the piece is covered with glaze, so none of the fired clay will be exposed. can you tell me the facts about this in a "matter of fact" way and/or refer me to some source that can answer my question? NO SARCASIM OR NON-VERIFIABLE ANSWERS PLEASE!!!