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Mike Avery
 
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Default Fibrament Stone Questions?

On 1/10/06, 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).




I have heard this several times, and have searched extensively on the 'net.
I have found *NO* evidence to suggest that unglazed quarry tiles contain
lead. I have repeatedly followed that statement on-line with a request that
anyone who has any evidence to the contrary contact me. So far, no one has
come forward.

A quick note on lead and glazes. Some glazes contain lead. If a lead
containing glaze is completely fired, the lead is inert and will not
contaminate foods or drink, at least as long as the glaze is unchipped and
unbroken. However, if the lead containing glaze is not fired correctly, the
lead in the glaze can be leached out. Tiles made in third world nations -
that is, the cheap tiles in import houses, sold from mysterious vans on the
side of the road, or purchased just across the border - are the ones most
often poorly fired.

The general equation is no glaze = no lead. In the past few decades, the
use of lead in glazes has declined, and even the third world potters have
gotten better. Still, it's cheaper to use an unglazed tile, so why take a
chance?

Lead usually migrates to food when acid is present, especially liquid
acids. So, putting a tomato salsa into a leaden container is not a good
idea. Nor a citrus fruit based punch. Most bread doughs are not terribly
acidic, sourdough being the exception. The other considerations are
temeprature, with high temperature speeding all chemical reactions, and
exposure time.

I don't think a lead glaze poses a serious health risk. Bread dough is
semi-solid, the exposure time is relative short. Once the dough forms a
crust, which is very quick, the migratio of lead is stopped. If you have
glazed tiles, using bakers parchment will probably protect the bread quite
effectively.

A comment on using tiles. Using sheet pans greatly reduces the
effectiveness of tiles. Jef Hammelman has some pictures of breads baked
directly on tiles (or a hearth) versus on sheet pans on tiles (or a hearth)
in his book. You lose a lot by using sheet pans. Bakers parchment is a
much better option if you are reluctant to put the bread directly on the
tiles.


Mike