On Tue, 10 Jan 2006 17:47:37 -0800
QX > wrote:

> I have heard from a friend that quarry tiles may contain lead, and you
> should ensure that they are lead free before cooking on them. Is this
> true? I know there are test kits available to test for lead in painted
> surfaces etc. Should I be concerned about lead, or is the concept an
> urban legend. (not knowing what is used to make the tiles).
>


Not lead, mercury.

In areas where BTUs come at a relatively high price - for example Mexico
and most third world countries - it's very common practice to mix mercury
in with the clay, because this significantly lowers the firing temperature
and saves you a lot of money in your fuel budget.

Nobody does this in developed countries where fuel isn't so hard to come
by. It's actually illegal in most developed countries.

Nearly all of the mercury sweats out during the firing process and ends
up in a puddle on the floor of the kiln, and is mixed into the next batch.

Some small amount of it does remain in the fired ceramic, and it can
certainly leech out.

How much? Hard to say. You probably wouldn't want to store food in
unglazed containers that were fired with mercury, but who stores food in
unglazed ceramics? Eating off of glazed dishes that were fired with
mercury, every day for your whole life, probably doesn't constitute
'significant' exposure to mercury.

Baking on a tile? Even less.

As for myself, I make a point of not eating heavy metals where i can
avoid it. Just doesn't seem like a good idea.

Depends what tile you're referring to how worried you should plausibly
be. If we're talking about those 'saltillo' tiles that are mottled pink &
yellow, about 3/4" thick, often misshapen, and quite porous, those are
almost certainly made in mexico as cheaply as possible, and it's very
likely that there is some tiny amount of mercury in them - but still
probably not enough to worry about for the occasional pizza.

If we're talking about made-in-the-USA good quality quarry tiles from
the hardware store or tile supplier, no, there isn't any mercury in 'em.
The EPA would have a field day.