Just to add my $0.02. I agree with the notion that the unglazing part is
mostly for moisture absorption, not due to the impurities in the glazing per
se. I don't know specifically what is in the glazing that might be bad for
you. But consider that in a place like California, crystal must contain a
warning label. Why? Because it contains lead. This is ridiculous, but true.
My concern is more about moisture absorption as it pertains to older stones.
Mine is not all that old, not all that used, but is terribly discoloured. I
know that's normal, but I'm not sure it doesn't hamper the moisture
absorption process. Similar to the way glazing seals the ceramic surface of
tiles, most of this materials that leach out and discolour the stone are
oils. Since oil and water don't like each other, I wonder if the moisture is
still absorbed as readily as with a virgin stone. Just wondering if somebody
could set my mind at ease.
BTW, I have both a real stone and a cheaper tile in my oven. The stone is
the only thing that sees food. The tile is on the top rack, trying to
recreate a pizza oven, at least on two sides. But I haven't really noticed
much of a difference. Yesterday I tried baking bagels, with the top rack
lowered so that there was only about a 1 inch gap above the top of the
bagels. I thought this might help brown them on top. But it didn't. I
finally ended up removing the top tile and broiling to complete the bake.
This did the trick.
Happy Baking.