The Fresh Loaf

News & Information for Amateur Bakers and Artisan Bread Enthusiasts

Lead test results on unglazed quarry tile and travertine tile

yankeedave's picture

Lead test results on unglazed quarry tile and travertine tile

I metioned this in a couple of threads and I know some people were interested in the results, so I'll put them here. I bought two tiles at a tile shop, an unglazed quarry tile and an "unfilled" travertine tile, and had them tested for lead. The results show 1.03 mg/kg lead for the quarry tile, and <0.662 mg/kg for the travertine.

Now I haven't yet determined the implications of those numbers as far as food safety is concerned, and the lab is not in the business of making those kinds of judgments or recommendations, so if anybody has any thoughts on those numbers, please weigh in.

blaisepascal's picture

I wouldn't eat the tile, at least.  According to a CDC site, allowable lead content varies.  In playground soils, lead content is limited to 400ppm, which would nearly 400 times the lead content of your quarry tile.  Another site had a case study of a group of ill children attributable to lead-contaminated Indian spices in the 1ppm range (about the same as your tile).  

How the experience of cooking with spices with 1ppm lead relates to cooking on the surface of a unglazed tile with a bulk level of 1ppm lead I'll let others weigh in.

yankeedave's picture

Yes, that works out to about 1 ppm. Lead in paint right now is limited to 600 ppm, and uncontaminated soil is <50 ppm. Assuming that leaching, if any, would result in far lower levels of lead being transferred to the dough, the risk seems almost nonexistent.

iconoclasthero's picture

The amount of Pb leached by bread is going to be heavily dependant on how acidic the bread is.  Sourdough would be a bad idea on a tile that has Pb available to be leached.  When you do a qualitative test for the presence of lead, you first try to leach it with acid (vinegar works, look up lead (II) acetate on wikipedia and then search the page for romans) and then test it with a potassium dichromate solution and watch for it to change colors.  i would have to think that there is a limit to the amount of Pb that is leachable so soaking the tile in vinegar would likely leach it all out.  you could also use CLR because lead is leached as a 2+ cation as is Ca and Fe.  If you test the resulting acetic acid solution and find no Pb in there, you're not leaching lead...


All of that said:  where do I find unglazed quarry tiles.  Lowe's and The Home Depot (THD) seem to indicate on their website that they sell it, but it appears to be a vicious lie.  I've been into their stores and spoken with their web people and it just seems like they don't carry it.  I saw the travertine there but I didn't know if it would explode at > 500F and send my pizza all over my oven. 


BTW, I participated in an EPA working group session in RTP on a rapid simple test method for Pb in paint...  wow, what a cluster.  I'm not sure how the governement ever gets such projects done based on my very small interaction with this group.




PeterS's picture

, if any, would leach out of the tiles. It also depends on the nature of the lead in the tiles and how reactive it is--probably very low. Also, the bread would only react with lead on the surface; it would not react with the lead in the bulk tile, i.e. below the surface. Furthermore, the rate of the reaction would be very slow: any liquid from the dough is likely going to vaporize when it comes in contact with a 400+ deg tile eliminating the medium to extract the lead out.

If the tile is dusting, the lead hazard might be significant if present in high enough concentration.

Leaching lead from ceramics and glazes is a much more serious hazard when dealing with liquids in vessels where it also can sit for a long period of time. Baking bread on a bare ceramic or glazed tiles is not for concern.

PeterS's picture

out baking bread.

It is easier, if the conditions are right, to extract lead or other undesirable elements (if present) out of a glaze than I probably implied.

That said, the conditions of baking are still not condusive to extraction and the hazard is likely minimal, at most.

Tanya's picture

I bought 6 boxes of unglazed quary tile at Home Depot several years ago to line up our 6 decks.  Lowes does not carry them.  They worked very well for over two years of heavy use, but when I went back to them this past summer, they only carried 3/8" thick tile instead of the previous 1/2" for the same price, about 45 cents per 6" sq.  The tile is made by Metropolitan and they have distributors around the country and 8" sq is also available from the distributors.  The boxes include a warning to avoid inhaling dust if you cut the tile.  The few pieces that I had to cut, I used a wet tile saw and made sure that the entire tile was well soaked and then washed them well before use.  Not aware of anyone growing any extra fingers or toes yet, but I'll have my eye on that ...  Anyway, they work well, the sourdoughs come out good and they're a lot cheaper than fancy baking stones.  500 deg F is not a problem at all, even when steam from the injectors hit them.  And when a tile gets too dirty, I just throw it away.

Haunz's picture

Your calculations are way off. 1.03 mg/kg and 0.662 mg/kg is equal to 1030ppm and 663ppm, respectively.


I am not sure I would be comfortable cooking my food on something like that.

yankeedave's picture

1 mg/kg = 1 ppm.

yankeedave's picture

I agree about Lowe's and Home Depot. The ones I've been to don't carry it and never have.

bonnibakes's picture

When I lived in New Bern, NC (1990-99) I bought unglazed quarry tiles that were thicker than the traditional thin ones (which they also carried) for under $1 each. They've been lining my ovens since then. I've closed by bakery/cafe and am thinking of taking the tiles out of the commercial convection oven before I sell it.

Caperchick's picture

Another concern I have regarding lead in tiles, is how lead reacts to high temperatures in the oven. Would there be a certain amount of lead released into the air when the tiles are heated?

Does anyone know if there is a way to test the lead content in older ceramic baking bowls? I've collected some over the years but am leary about using them for my doughs.

Mini Oven's picture
Mini Oven

:)   for info

yankeedave's picture

I don't think that heat alone releases lead "into the air." You need contact between the tiles or bowl and the bread or whatever you're baking, some moisture, and from what I've read, acidity to leach out the lead. But if you're baking in these bowls, some of those conditions may be met, so personally I wouldn't use them if I wasn't sure about their lead content. I don't think there's any way to test them without damaging them, though. With my tiles they had to grind up a little bit and test the powder.

Hank Gurdjieff's picture
Hank Gurdjieff

I'm thinking of picking up some quarry tiles for bread and pizza baking, saw this thread, and then found the following:

The Center for Environmental Health in Oakland, CA, offers free lead testing. You only have to mail in (or drop off, if you're nearby) a small chip of tile and they'll test it and send you the results. They're local, so once I get around to getting some tiles I'll have them tested and post results but it seems there are many colors/sources of tiles and content will surely vary. 

Hmm, lead - I wonder if lead paint is why I keep finding my dog licking the wall with a far-off, dumb look on his face...

ryster's picture

used some standard (3/8") filled and honed travertine tiles, upside down on the lowest rack, heated in a 455 deg. oven, baked some HUGE calzones, They came out perfect. My bread/pizza bakes just fine on aluminum pizza trays but thought I'd give these stones a try, not sure how they would hold up long-term, but I plan on using these 3 stones until they give, as I only bake breads maybe once a month.

dabrownman's picture

before sliding in the oven with a peel.  No leaching with parchment if you discount the silicone in the parchment :-0

yankeedave's picture

One of the experiments I keep meaning to do is to bake two bread loaves, on tile or a stone, side by side, one with parchment, the other without. When I use parchment, I usually slide it out halfway through the baking process, but even so, it seems to me that when I use parchment, the bottom doesn't get quite as charred. Maybe that's just a subjective perception. And it's not necessarily a bad thing, but if you're using a stone or tile, presumably you're looking for charring. And once the bottom is dry, I think leaching becomes much less of an issue, because it's the water that acts as a medium for the transfer of lead.