Pizza Stones: Rip off? Quarry stones: Safe?

November 14, 2010 7:29 AM

Are unglazed quarry tiles safe for use in an oven?

I have googled this question, but I seem to only get discussion boards and Amazon reviews saying "yes they are," "no they aren't." I'm hoping someone with some expertise in the hive mind can shed light.

Basically, I want a baking stone. At Amazon, the Old Stone Oven 4467 is $36, which is cheaper than at Sur La Table (of course). However, the idea of using a $1 "quarry tile" is appealing... if it's safe. Getting heavy metals poisoning over the course of a decade doesn't exactly seem worth the $30 savings.

How would I buy a quarry tile at, say, Lowe's? How do I know if it's food safe? Has any research been done on this topic? How do I prevent myself from buying a stone whose main ingredient is Reconstituted Stone Product, courtesy of 3M?

posted by sonic meat machine to food & drink (20 answers total)

More immediately, I'd worry about what thermal stress would do to something that wasn't intended to be put in a 450-degree F. oven. I've seen items "explode" before--although the metal oven might contain the impact, sweeping out the shattered bits from all the nooks and crannies afterward is not fun. I'd be interested to hear if anyone has direct experience with a particular type of tile.

(I use an Oneida baking stone that I bought at Bed, Bath, and Beyond. A check of their website shows the same one currently at $19. Sales and coupons could drive that lower, if there's a brick/mortar one in your area.)
posted by gimonca at 7:47 AM on November 14, 2010

Good Eats - Flat Is Beautiful (text transcript, search for 'quarry')
posted by buckaroo_benzai at 8:05 AM on November 14, 2010 [1 favorite]

I'm aware of that bit, buckaroo; that's why I'm willing to consider it. I'm not quite sure how much I trust the building stores I have available to me, though. That's the main issue: if it's safe, how do I guarantee that I get the safe product from the building store?

gimonca, I'm not that worried about thermal stress since it's so cheap and these tiles are fired in kilns.
posted by sonic meat machine at 8:19 AM on November 14, 2010

I got a cheap one from Target, with the idea that I'd try it out and get a nicer one if I liked it. It's been a few years now, and the thing is still in great shape, and it does exactly what it's supposed to (I use mine semi-regularly for bread-baking).
posted by ella wren at 8:21 AM on November 14, 2010

How do I prevent myself from buying a stone whose main ingredient is Reconstituted Stone Product, courtesy of 3M?

You could get the manufacturers details from your building store, approach/phone them, and ask whether they consider their tiles safe for use as pizza stones. If they say no, believe them.

To beanplate it, you could also ask the manufacturer to tell you the precise origin of the clay and the stone that goes into their tile, and check the chemical composition of those with a geologist at your local college/university. Then take that information to your doctor (although the geo should be able to give you a non-medical opinion).
posted by Ahab at 8:27 AM on November 14, 2010

We use an old cast iron skillet. (It got replaced by a bigger one with two handles, and we had nowhere to store it, and the oven thermostat is kinda wonky anyway, so.) It holds heat well, and catches drips, too!
posted by BitterOldPunk at 8:49 AM on November 14, 2010

BitterOldPunk, do you cook directly on the cast iron, or just use it as a "heat reservoir?"
posted by sonic meat machine at 9:00 AM on November 14, 2010

I have only semi-scientific info to offer, but I will say that I've been using some unglazed tiles as pizza stones for 2 years. They're natural clay, about 8x8 and were $1. No one knew what "quarry stones" were at my home depot.

Heavy metals, even radioactive materials, are possible in any natural product— fancy pizza stone or not. Also, any stone you put in there will break eventually.

If you're concerned about it, a piece of baking parchment paper will keep your food from directly contacting the stone, but still allows for pretty good browning. Its also much easier to move pizzas or bread on and off. Paper that isn't in contact with the food will probably get pretty dark and crumble away, but even at 500°, does not ignite.
posted by fontophilic at 9:07 AM on November 14, 2010 [1 favorite]

That's the main issue: if it's safe, how do I guarantee that I get the safe product from the building store?

You can't. The tiles aren't intended for food use, so no one is going to be able to tell if you if any particular tile is safe or not. You can call the manufacturer and get some information that way, but they certainly aren't going to be willing to guarantee that their tiles are food safe. Personally, if the manufacturer told me that certain tiles were made of clay and nothing else, I would consider the risk very low and be happy to use them but your tolerance and perception of risk may be different. When you want to use a product for something it isn't intended for, you have to do your own risk assessment and research and there won't be any guarantees.

Also, like BitterOldPunk, I find that cast iron is better for pizza (your oven doesn't get hot enough to heat the stone up to cook the crust quickly, but you can heat up the pan on the burner to a much higher temperature, throw the pizza on it and then put it under the broiler for a couple minutes). For bread, though, I prefer a stone (with a flowerpot for a lid), though a cast iron dutch oven is good too.
posted by ssg at 9:22 AM on November 14, 2010

We leave the old skillet on the lowest oven rack and bake on the two above it. Works fine using the skillet to hold heat. It does take a bit longer to bring the oven to temp, but checking an oven thermometer instead of relying on the oven's built-in sensor solves that problem.
posted by BitterOldPunk at 9:41 AM on November 14, 2010

This may be a bit tangential for you but here goes: I worked for a large art materials manufacturer, and we sold earth based pigments: titanium, lead, cadmium, earth oxides to the public. Most natural ores will contain trace elements of lead and cadmium, which are not good to ingest at very low levels. If the stone were not intended for consumption grade use, and is heated to high temperatures with food substances, you cannot be certain there will be no migration into your food.

Companies that manufacture children's jewelry, for example, have been struggling with the issue of trace cadmium and lead in their materials, and the fact that children suck on the jewelry. Those who want to sell it to you will tell you its safe, people who monitor toxic levels of metal will tell you its not safe.

Personally, I would stick with materials I know are safe. Plastic and heavy metal leeching are two things I try to minimize in my diet.

Believe it or not, the most common call I got from the public were from people who ate their art materials, then called me to find out if they were going to be ok.
posted by effluvia at 10:04 AM on November 14, 2010

However, the idea of using a $1 "quarry tile" is appealing... if it's safe. Getting heavy metals poisoning over the course of a decade doesn't exactly seem worth the $30 savings.

The people at your hardware store will not have any information about whether stones are safe for your oven any more than they would be able to guarantee that any item is effective or recommended for a non-standard use. They can't recommend the safety of a storage bin as a turkey-brining-container, drilling holes in 5-gallon buckets to use as cherry tomato planters, or converting a trash can into a smoker, either.

Okay, I'm not a chemist or a geologist or a tile-manufacturer or a poison-control expert or an environmental epidemiologist. I am highly skeptical of the price of pizza stones and am instead using unglazed tiles from Lowe's in my oven.

The whole point of the tiles is that they're very hard and durable, so I'm not concerned about the material flaking into my food and being ingested. (If one gets damaged, I've got a box of backups.) And it's not as if the heavy metals possibly present in the tiles are volatile. So it seems the only danger is heavy metals leaching into food directly placed on the stone.

For us, this is just pizza. We make pizza once every week or two, but only for the coldest half of the year (we avoid turning the oven to high in warmer months since we don't have A/C.) Not exactly a comparable level of exposure to the leaded water pipes or even everyday cooking and drinking vessels, right? So, do I think that eating half of a pizza twenty times a year is increasing my lifetime exposure to heavy metals in any significant way? Eh, nope. I really don't.

Buy the box of tiles and give 'em a whirl. If you find that they make you nervous, you can still leave 'em in there to improve your oven's heat-holding efficiency. Or use them as trivets, stepping-stones in your garden, tile the top of an outdoor table. Or donate them for use by crafty types.
posted by desuetude at 11:20 AM on November 14, 2010

Heavy metals are usually deliberately concentrated in glazes, not clays, (because heavy metals and toxic compounds produce color) so working with an unglazed tile is the smartest way to go.

You may be able to find more info about the clay source and make a more informed judgment. Personally, I would buy a tile, heat the living shit out of it in my oven, and see if it smelled like burnt plastic or other treatments. If it just smelled/looked like a hot piece of clay, it's almost certainly as safe as any other tile. Now, before anyone jumps on me, you won't be able to test heavy metal content this way. But again, you probably don't have to worry about it, because it wasn't deliberately added in large concentrations as a glaze.

Remember, fired clay is basically fused silica, which is as inert as you can get.
posted by fake at 11:33 AM on November 14, 2010

To be honest, I don't think heavy metals are that big of a concern here, but even if you somehow DID manage to get the leadiest tile out there I'm not sure you'd have that much to worry about at pizza baking temperatures. Your not going to get it nearly as hot as the temperature at which it was fired and at reasonable baking temperatures you're not going to get a whole lot of lead vapor.

In terms of what is going to kill you over decades, the typical American diet is probably a million times more dangerous than diffusion of lead from a solid clay tile to pizza crust.

Getting plastic binders or a sealant or something other than fire hardened clay would be my major concern. I'd do what fake suggests (only I'd do it on my BBQ grill so as not to make the house smell like eau de flaming garbage bag if it turns out that I picked something that wasn't acceptable).
posted by Kid Charlemagne at 11:43 AM on November 14, 2010

Thanks for the answers, guys. I think I will just bite the bullet and buy a baking stone. $36 won't break the bank, and it's worth it for the peace of mind. I've marked several answers as "best," because together they influenced my decision the most.

I don't trust "burning out" the plastic/chemicals and so forth. Half the noxious crap that could be in there could be odorless when it becomes vapor. Furthermore, I'm not as worried about intentional inclusions as I am "accidents" or inputs which are within tolerance for floors but which aren't necessarily so great when heated to 500° F and in contact with food.

I know that the "American diet" is much maligned (and with good reason), but I try to cook most of my meals (Mrs. Machine cooks, as well), so saying "it's not as risky as eating McDonald's every day" isn't very relevant. :)

The stone I will purchase, in all likelihood, is this one, recommended by Cook's Illustrated (and about $20 cheaper on Amazon than through their recommended vendor, King Arthur Flour).
posted by sonic meat machine at 1:20 PM on November 14, 2010

I don't trust "burning out" the plastic/chemicals and so forth.

To be clear, my suggestion was to use this to eliminate tiles from your selection (stinky ones are a clear no), I was in no way suggesting that you could eliminate plastics by burning them.
posted by fake at 1:49 PM on November 14, 2010

Fair enough. Point stands, though; if it has some newfangled Miracle Chemical that makes it impervious to dog pee (or whatever) in it, it may turn into Dow-Corning DeathGas at high temperature without so much as a sniff of scent...
posted by sonic meat machine at 2:08 PM on November 14, 2010

If it makes you feel any better about spending the money, though I received it as a gift I have a ~16" dia pizza stone that works great. It's like 13 years old. I never take it out.
posted by rhizome at 2:37 PM on November 14, 2010

Fair enough. Point stands, though; if it has some newfangled Miracle Chemical that makes it impervious to dog pee (or whatever) in it, it may turn into Dow-Corning DeathGas at high temperature without so much as a sniff of scent...

Hey, if you'd rather not use construction materials for cooking, that's totally cool, but I don't think that secret mystery chemicals like this are a likely concern. Unglazed ceramic tile is pretty basic, it's composed of natural clay and shale.
posted by desuetude at 7:04 PM on November 14, 2010

We have a Pizza Stone that we have used every Friday for like 15 years. But I can't count the number of times I've read that "you can use inexpensive tiles from your home store!"

Hmmm, try the blog post (for the "Artisan Bread in 5 Minutes a Day" books) where they discuss lots of alternatives: www.artisanbreadinfive.com/?p=2159
posted by wenestvedt at 12:25 PM on November 15, 2010