Unglazed clay and stoneware cookware starts the same way: no glaze, no coating, nothing added after the fire did its work. What you’re holding went in as clay and came out however that firing left it, and that’s the only surface it will ever have. The differences you notice from piece to piece, the color, the weight, how rough or smooth it feels, come from how hot the kiln ran and how far the clay got toward becoming stone. None of it was sprayed on afterward.
People have cooked this way for thousands of years, long before anyone thought to seal a pot. Left porous, clay soaks up water before cooking and lets it go slowly as steam, so food stays moist without you doing much. Fired hot enough to seal itself instead, it does almost the opposite: it holds dry, even heat long enough to crisp a crust. Same starting material, two different jobs, depending on how it was fired.
On Glaze and Lead
Most of what worries people about clay cookware is actually a worry about glaze, not the clay itself. A 2020 study in the Beni-Suef University Journal of Basic and Applied Sciences tested lead levels in water boiled in glazed versus unglazed clay pots. Water from the glazed pots came back significantly higher than a plain-water control, 26 micrograms per liter after two hours, 36 after four. Water from the unglazed pots showed no significant difference from that control.
That’s reassuring, but it’s not a free pass. Independent lab testing by Lead Safe Mama, using the same X-ray method the Consumer Product Safety Commission relies on, found 29 parts per million of lead on the food-contact surface of one unglazed, mass-produced stoneware baking tray. That’s a reading of what’s in the material itself, not proof of how much would end up in your food, and the distinction matters. But it happened on a nationally sold, factory-made piece, not some sketchy import, which is exactly why “it’s unglazed” isn’t something you get to say and stop thinking about.
Where to Start
A reliable first piece. Machine-pressed stoneware or a mass-produced terracotta pot, inexpensive enough to find out whether this way of cooking is for you before you spend real money.
A piece to keep. Hand-formed by someone who tests each batch, in theory. That claim is only as good as the testing behind it, and the tray above was a big, established brand, not a small studio. If a maker tells you their unglazed work is tested, it’s fair to ask what that testing actually was before you take it as settled.
There’s real disagreement over whether a clay pot needs a fresh soak every time you cook in it, or just the first.
On Porosity
Earthenware is fired low, somewhere around 980 to 1,100°C. That’s too cool for the clay to ever fully vitrify, which is just the word for clay particles melting together into something closer to glass. Left short of that point, the clay stays genuinely porous, soaking up something like 10 to 15 percent of its own weight in water. That’s why you soak a clay pot before you cook in it.
Stoneware is fired much hotter, up around 1,200 to 1,300°C, hot enough that the clay partly seals itself shut. Water absorption drops below 2 percent, sometimes under half a percent. That’s also why stoneware never needed glaze to hold water in the first place. Soak a piece like that the way you’d soak a terracotta pot, and you haven’t helped anything. You’ve just trapped moisture that can crack it the moment real heat hits.
Here’s the part that tends to surprise people: the porous piece is actually tougher against a sudden flame than the sealed one. In Digitalfire’s own direct-flame testing, unglazed terra cotta held up against a sidewall flame for around 30 seconds before cracking, while typical stonewares and porcelains failed in 10 to 15. That’s not a reason to skip heating a clay pot gradually from cold, though. What cracks a soaked pot isn’t the clay itself. It’s the water trapped inside, turning to steam faster than it can find a way out.
Unglazed Clay and Stoneware Cookware, Side by Side
Both go into the kiln with nothing on them, which is the entire idea behind unglazed clay and stoneware cookware: whatever the fire decided stands, nothing gets added afterward. But “unglazed” gets used for two genuinely different materials. Earthenware is old-world clay pot cooking, tagines, cazuelas, handis, built to hold and slowly release moisture over a long cook. Stoneware is what pizza stones and bread pans are made from, and manufacturer care instructions consistently warn against oil or soap on it for the same reason: the surface is porous enough to soak both straight in. Choose earthenware for a long, moist cook. Choose stoneware for dry, high heat. They’re not standing in for each other.
On Cracking
A crack in fired clay doesn’t heal the way rust reverses on iron. Once it’s cracked, it stays cracked, patched at best. Most cracks come down to the same few causes: heat applied too fast, a soaked pot rushed onto high heat, or a cold pot set straight onto a hot burner. None of that is a flaw in the clay. It just needed more time to catch up to the heat than it got.
On a Life of Use
A well-used piece of unglazed earth changes color over time. Oil and stock work into the surface and darken it, and that’s not something gone wrong. It’s just what happens when a piece has actually been cooked in. Wipe it out, let it dry, and it’s ready for the next meal.