Yes, I've searched newsgroup archives, yes I've read all the arguments that unglazed quarry tiles are safe, and yes I've been baking directly on them for years and I'm still alive. But the time has come for my wife and I to see if we can pass our genes on to the next generation, and so we're being intentionally paranoid about food safety issues. From what I've read, the argument that they're safe seems to be that there's no evidence that they're not safe, and nobody has died or gotten sick or lost IQ points because of them (as far as we know), so there are more important things to worry about: they're innocent until proven guilty.
My quarry tiles are dark red-orange in color. Red to me means most likely iron, but perhaps cadmium. And who knows what else is in there. Maybe lead, maybe not. Maybe whatever's in there won't transfer to the bread anyway, but then I do bake mostly sourdough, which is a bit acidic. I don't know the origin of the clay used to make my tiles -- maybe it was Mexico or China, where perhaps the regulations about lead and heavy metals are a bit more lax. That's enough maybes for me that, being intentionally paranoid, I'm going to take a "guilty until proven innocent" stance. Unless anybody can point me to a supplier of tiles who will actually vouch for the composition of their product, down to trace elements in the single-digit ppm (parts per million) range, or else another reliable source of evidence that they're safe, I'm going to replace my trusty old quarry tiles with something NSF or FDA approved.
FLAME-RETARDANT DISCLAIMER: I'm not saying that quarry tiles aren't safe -- I believe they probably are, and have no evidence to the contrary -- but I'm just being paranoid. I don't encourage anybody else to throw away their quarry tiles and buy an expensive baking stone. If anybody can actually provide evidence to prove the innocence of quarry tiles, I would be truly grateful, because they work well and are cheap.
So on to what to replace it with -- there seem to be two contenders for the home baker: the commonly available cordierite "pizza stones", and the FibraMent stone from AWMCO
On the other hand, I once owned a cheap baking stone (probably cordierite, but I'm not sure), which cracked after only a few months of use, and I took what I thought was good care of it -- avoiding putting water on a hot stone, and always preheating the oven with the stone in it. The greatest stress was caused by transferring the (cool) stone in and out of the oven, since I don't want it in there when I'm only using the oven to quickly roast some vegetables, for example, because pre-heating the stone is a waste of time and energy in that case. Anybody who's owned a FibraMent for a while care to comment on its durability, or on what hoops you have to jump through to take advantage of their 10-year warranty?
Anybody care to comment on baking characteristics of cordierite vs. FibraMent?
TIA for any info/advice,