clay. it's not encased at all because the tiles are only glazed on top of
porcelain.

neither the glaze nor the tile may be safe. there's a lot of glazes that
aren't food safe (contain lead, cadmium, etc) and could leach metals from
either a basic or acid solution in contact with it. you'd have to find out
what is in them from the manufacturer, and they probably don't know since
tiles typically don't have a msds.

"Harry Muscle" wrote in message
...
Anybody know if porcelain tiles (like the ones that go on the floor) are
safe in an aquarium. Sinks and such are made of porcelain, so the
porcelain
itself is fine, but the tiles are colored porcelain. Anyone know what
kind
of chemicals they use to color porcelain, and if this stuff would be
pretty
well encased inside the porcelain so none of it leaches out? I'm hoping
to
use these tiles for a background.

Thanks,
Harry