What the glaze leaches
This is the part with actual federal numbers attached. Lead and cadmium have published limits, measured with a specific lab test, and they are different for a mug than for a plate. Everything else about a glaze is unregulated.
Pottery safety reference
Is Handmade Pottery Food Safe?
Almost always. And when it is not, the reason usually has nothing to do with the fact that a person made it by hand. Here is what the rules actually say, what the research settles, what it does not, and how to judge a piece sitting in your cupboard right now.
The short answerOne Two Three
Three things decide it, and only one is the glaze
A piece of pottery is safe to eat off when nothing harmful comes out of it into your food. In practice that is a question about three things, and people almost always ask about the third one first.
What the clay under it does
The forgotten one, and often the bigger problem. A porous, underfired body holds water whatever is painted on top of it. That is where odor, weeping and a genuinely unpleasant surface come from.
How you wash it
The one nobody expects to matter. In the one published test on crazed pottery and bacteria, how the tile was cleaned mattered more than whether it was crazed at all. More on that below.
The thing worth saying at the top. Almost every documented case of ceramics poisoning someone traces back to lead glaze, usually on imported traditional ware, not to studio pottery fired in an electric kiln with commercial glazes. The risk is real and it is narrow. Knowing where it actually sits is the whole point of this page.
What it means
Food safe is a test result, not a promise
There is no federal certification a potter applies for. What exists is a pair of FDA action levels for how much lead and cadmium can leach out of a glazed surface, and whoever sells the finished piece carries the responsibility for meeting them.
There are no FDA regulations that authorize lead for use as a color additive or food additive, including as a component of foodware, cookware, or food contact surfaces.US Food and Drug Administration
The test behind those numbers is the same every time: fill the piece with four percent acetic acid, which is roughly household vinegar, leave it for twenty-four hours at room temperature, then measure what came out. The limits are in micrograms per milliliter, which is the same number as parts per million.
Lead, micrograms per milliliter
| Vessel | Lead limit | Judged on |
|---|---|---|
| Flatwareanything under 25 mm deep, so plates and most saucers | 3.0 | average of 6 |
| Small hollowware, not cups or mugsdeeper than 25 mm, under 1.1 liters | 2.0 | any one of 6 |
| Cups and mugssmall vessels for hot drinks, usually about 240 mL with a handle | 0.5 | any one of 6 |
| Large hollowware, not pitchers1.1 liters or more | 1.0 | any one of 6 |
| Pitcherslarge vessels with a lip spout, for juice and other acidic drinks | 0.5 | any one of 6 |
Cadmium, micrograms per milliliter
| Vessel | Cadmium limit | Judged on |
|---|---|---|
| Flatware3.0 above for lead, 0.5 here | 0.5 | average of 6 |
| Small hollowwarea mug is judged here for cadmium | 0.5 | any one of 6 |
| Large hollowware1.1 liters or more | 0.25 | any one of 6 |
Read the mug row again. A plate is allowed 3.0 and a mug is allowed 0.5, which is six times stricter, because you hold hot acidic liquid in a mug for a long time and food sits on a plate briefly. Almost nobody knows this, including plenty of people who use the phrase food safe every week. The cadmium guide, separately, has only three categories and no mug row at all, so a mug is judged as small hollowware there.
Sources: FDA Compliance Policy Guides 545.450 (lead) and 545.400 (cadmium), issued 1980, last revised 2005 and still operative. Flatware means anything less than 25 mm deep. Small hollowware is under 1.1 liters. Note the judging column: flatware is assessed on the average of six pieces and everything else on any one of six, which is the stricter test.
Where the risk actually sits
Four things that are true and one label that is not reliable
Lead free on a label is not proof
The FDA issued an entire guidance document in 2010 because imported traditional pottery labeled Lead Free was turning up with leachable lead in it. One named mechanism is a kiln previously used for lead glazes contaminating lead free work fired in it afterwards. The label describes an intention, not a measurement.
Bright red, orange and yellow are the flagged colors
Cadmium is the pigment chemistry behind those colors, which is why California and the FDA both name them specifically. The FDA also flags them as a lead marker in traditional pottery. A bright red decorative rim is worth more attention than a brown stoneware glaze.
A food safe glaze can still fail on a pot
When a glaze manufacturer tests a glaze and passes it, that covers that glaze, fired as directed, by itself. Layered over another glaze, underfired, or put over a raw colorant it is a different chemistry, and the test no longer describes it.
Trace amounts are not the issue
It is not illegal for foodware to contain traces of lead or cadmium. What matters is how much leaches out under the test. That distinction is why sweeping claims in either direction, safe or unsafe, are usually wrong.
The most misunderstood one
Crazing, and what the one real test found
Crazing is the fine web of cracks in a glaze surface. It happens when the glaze and the clay shrink at different rates on cooling, so the glaze ends up stretched over the body and relieves the tension by cracking. It can appear straight out of the kiln or turn up years later.
The common belief is that a crazed piece is unsafe because bacteria live in the cracks. In 2018 a team published the test in Ceramics Monthly: crazed and non-crazed tiles were dosed with about a billion bacterial cells each, then cleaned four different ways.
What they found on the crazed tiles
Bacteria survived wiping, and survived washing, right up through increasingly stringent cleaning. Then a normal dishwasher cycle removed or killed all of it, with no colonies detected afterwards.
What they found on the tiles with no crazing at all
Bacteria were recovered from the non-crazed tiles that were only wiped and dried. A perfectly smooth surface, cleaned badly, still grew things.
The use of heat, soap, and water kills or removes bacteria in even crazed surfaces, though they are commonly and mistakenly thought to be totally non-food safe.Ceramics Monthly, November 2018
So how you wash it mattered more than whether it crazed. That is the finding, and it reframes the question.
The honest caveat, because there is one. This was a magazine technical column rather than a peer reviewed paper, run on one organism. And the technical position against crazing is not about bacteria in the cracks so much as what is under them: if the clay body below is porous, the cracks give water a route into it. On a vitrified stoneware body, crazing is mostly a durability problem, because a crazed glaze is under tension and a piece under tension is weaker. On a porous body it is a real hygiene question.
Which puts the answer back on the clay, not the glaze.
In your kitchen
Dishwasher, microwave, oven, freezer
Most of what goes wrong here is thermal shock, which is what happens when one part of a piece changes temperature faster than another and the stress has nowhere to go. Ceramics are brittle, so the stress becomes a crack.
Dishwasher
Usually fine, and per the crazing test above, better for hygiene than a wipe with a cloth. What it does do over years is dull some surfaces and work on any unglazed foot ring. Metallic lusters and gold rims should not go in at all.
Microwave
Microwaves pass straight through ceramic, which is why it is a normal material to heat food in. Metal reflects them instead, so anything with a luster, a gold band or a metallic glaze will arc and spark. Thick or unevenly walled pieces also heat unevenly.
Oven
The hardest of the four on a pot. Silica in a fired body can change volume somewhere between about 100 and 270 degrees C, which an oven crosses every time. Go in cold, come out to a dry surface, never straight onto a wet counter.
Freezer
The freezer itself is not the problem. Frozen to hot is. A frozen dish going into a heated oven is one of the largest thermal shocks you can hand a piece of pottery, and it is where most casserole dishes die.
One counterintuitive thing worth knowing. A porous earthenware body can survive thermal shock better than a dense porcelain one, because the tiny gaps in it stop a crack from travelling. Vitrified and shock resistant are two different goals, and they pull against each other. A piece can be excellent at one and poor at the other.
Under the glaze
The clay is doing more of this than the glaze is
Absorption is the share of its own weight a fired body will take back on in water. Porcelain fired properly can reach effectively zero. Stoneware usually settles somewhere around 1 to 3 percent. Earthenware sits higher, which is the entire reason a terracotta pot sweats.
A piece that is porous inside does not stop being porous because a glaze covers it. Water gets in at the foot ring, at a chip, through a crazed line. What follows is a mug that stays damp, smells after a week, weakens over time, and leaves a ring on a wooden table hours after it was dried.
And a fair warning about what does not exist. There is no federal absorption limit for dinnerware. The FDA action levels cover leachable lead and cadmium and nothing else. The 0.5 percent figure people quote is the ANSI definition of porcelain tile, which is a different product with a different standard. Anyone quoting a legal absorption threshold for a mug is quoting something that is not there.
Our clay body comparison chart lists published absorption for 114 clay bodies, at the cone each one was measured.
A piece you already own
How to judge it, honestly
You cannot tell by looking. Everything here is triage, not a test. The only way to actually know is a laboratory leach test, which for one mug costs more than the mug. What you can do is work out whether the mug is even in a risky category.
- Ask where it came from. The FDA names five things that raise concern in traditional pottery: handmade with a crude appearance or irregular shape, antique, damaged or excessively worn, bought from flea markets or street vendors or sources that cannot be verified, and brightly decorated in orange, red or yellow. That list was written about imported traditional lead glazed ware, mostly from a handful of countries. It is not a verdict on studio pottery, and it is worth reading in that context rather than as a rule about anything made by hand.
- Look at the inside surface. A raw oxide wash, an unglazed stained surface or a chalky matte inside a bowl is a different thing from a glassy fired glaze. Anything powdery, dusty or that marks your finger does not belong under food.
- Check the foot ring. Turn it over. If the unglazed clay looks and feels like chalk, and a drop of water soaks straight in and darkens it, the body is porous. That tells you about durability and odor, not about lead, but it is the one physical test you can genuinely do at the sink.
- Note anything metallic. Gold, platinum and luster bands are not microwave safe and the dishwasher wears them off. This one is easy to see.
- If it is old, imported, brightly painted and you do not know its history, stop using it for food. There is no way to fix a piece that leaches. The FDA is explicit that no amount of washing or boiling removes lead from pottery. It can still be a lovely thing on a shelf.
About those home lead swab kits
This is the part where the honest answer is that the evidence does not agree with itself, so here is both halves of it.
The regulator says no
A 2007 Consumer Product Safety Commission study of consumer lead kits found 56 false negatives out of 104 results, and concluded consumers should not use lead test kits to evaluate consumer products. The line that matters most for pottery: none of the kits consistently detected lead when it sat under a non-leaded coating. A lead bearing layer under a clear glaze is exactly that case.
The one ceramics study says maybe
A 1998 peer reviewed study tested four lead kits and one cadmium kit on pre-1970s ceramic dishes and then leach tested the same dishes. Fewer than 10 percent of the dishes that actually failed gave a false negative on the lead kits. The cadmium kit missed 29 percent. Its conclusion was that lead kits are useful for screening old dinnerware and the cadmium kit is not.
Both are real. The study is the only one done on ceramics specifically, and it is nearly thirty years old, on kit formulations that no longer exist. The regulator tested a wider range of products more recently and came out against them. What a swab can reasonably do is flag an obvious problem. What it cannot do is clear a piece.
Testing by a qualified laboratory and trained personnel is the only way to accurately assess the potential risk posed by a consumer product that may contain lead.Consumer Product Safety Commission
If you made it
Then the claim is yours, and that is a different page
Everything above is written for the person holding the mug. If you are the person who made it and you are about to write food safe on a label or a listing, that sentence belongs to you rather than to your glaze supplier, and there is a whole process behind saying it honestly.
We wrote that one separately, because it is a different job: which four claims people make casually, what each one commits you to, what to test on a tile, and what to write only after it passed.
The ones that come up
Questions people actually ask
Is handmade pottery safe to eat and drink from?
Ordinarily yes. Studio pottery fired in an electric kiln with modern commercial glazes is not where the documented problems come from. The cases that reach the medical literature almost all involve lead glazed traditional ware, usually imported, often antique or brightly painted.
Does food safe mean it was certified by someone?
No. There is no federal certification and no body a potter applies to. What exists is a pair of FDA action levels for leachable lead and cadmium, a defined lab test, and the expectation that whoever sells the piece has met them. Food safe is a claim about a test result.
Can I use a crazed mug?
Generally yes, if the body under it is vitrified and you wash it properly. The one published test found a dishwasher cycle cleared bacteria from crazed tiles entirely, while smooth tiles that were only wiped still grew them. On a porous, underfired body it is a closer call, and a crazed glaze is also a weaker one.
Is handmade pottery dishwasher safe?
Almost all of it, and the dishwasher is the better choice for hygiene. The exceptions are pieces with gold, platinum or luster decoration, which come off, and anything the maker specifically said to hand wash. Long term, hot cycles will slowly dull some surfaces.
Why can I not put my mug in the microwave?
If it is plain glazed ceramic, you almost certainly can. Microwaves pass through ceramic. What sparks is metal, so anything with a luster, a gold rim or a metallic glaze stays out. Very thick or uneven pieces also heat unevenly, which is a thermal shock risk.
Do lead free glaze labels mean the pot is lead free?
Not by themselves. The FDA issued guidance in 2010 after finding leachable lead in pottery labeled Lead Free, and named kiln cross contamination as one route: a lead free glaze fired in a kiln previously used for lead glazes. The label describes the glaze as sold, not the finished piece.
Are home lead test kits any good on pottery?
They are a screen at best. The CPSC found more than half of results were false negatives and advises against using them on consumer products, and noted specifically that the kits miss lead sitting under a non-leaded coating. The one ceramics specific study is more positive and is from 1998. A positive result means something. A negative one does not clear the piece.
What about pottery fired at The Clay Hole?
We bisque to cone 05 and glaze fire to cone 5½, which is cone 5 with a twelve minute hold, using commercial glazes from named manufacturers. What we cannot do is test your individual piece, because a claim about one pot depends on how it was glazed and what went on it. The claim on a finished piece belongs to whoever made it.
The short version
Know the piece, not the category
Handmade is not the risk factor. Lead glaze is, and it lives mostly in old and imported traditional ware. A vitrified body under a properly fired commercial glaze, washed in a dishwasher, is about as unremarkable as a dinner plate gets.
And if a piece is old, brightly painted, from an unknown source and holding your morning coffee, that is the one worth thinking about.
More reading: can I put a kiln in my garage, why did my pottery do that, the pottery dictionary.
- FDA Compliance Policy Guides 545.450 and 545.400, the 2010 guidance on imported traditional pottery and the Lead Free label, and the FDA questions and answers on lead glazed traditional pottery.
- Consumer Product Safety Commission staff study on home lead test kits, October 2007. Sheets, R.W., Science of the Total Environment, 1998, on home test kits and ceramic dinnerware.
- Coppage, Farsin and Runyen-Janecky, Techno File: Dirty Dishes, Ceramics Monthly, November 2018, on crazing and bacteria.
- California OEHHA Proposition 65 fact sheet on cadmium. Digitalfire on crazing, thermal shock and clay body porosity.
- Read 24 September 2026. This page is general information about pottery, not advice about any particular piece.