Food Safe Glazes

Which glazes can go on a mug, which belong on the outside only, and how to keep a good rating from going bad.

Rated for food
465
Cleared not rated
144
Never for food
17
Food Safe Glazes at The Clay Hole

Look up any glaze we carry

Start typing a glaze name. You get the tile we fired, the answer, and where the answer came from.

This is the question behind almost every functional pot anyone makes here, and the Bible used to answer it one glaze at a time. Now it answers for all of them.

Four answers cover every glaze on this page. Rated for functional ware means the maker states it is safe for ware that holds food. Cleared, not rated means the maker clears the materials and stops short of rating the finished pot. Outside of the pot only means keeping it off anything food touches. Not dinnerware safe means never for food, at any thickness, on any pot.

A word about what food safe means, because it is looser than it sounds. Makers test a glaze as a material, fired to their specification on their clay. What comes out of our kiln is your glaze, on your clay, at your thickness, in our schedule. The rating tells you the recipe is sound. It does not certify your pot.

Three things void a good rating no matter what the jar says. Crazing, that fine web of cracks, gives bacteria somewhere to live and lets liquid reach the clay. Underfiring leaves the glaze not properly melted. And a thin or crawled coat leaves bare clay where you thought there was glaze.

Two things are deliberately not on this page. Raku is never food safe, and it has its own collection. So are the low-fire crystal glazes we keep for raku firings. Of what is left, twenty three glazes belong off food surfaces one way or another. The rest can go on a pot you eat from, as long as you fire it properly.

The safe habit costs nothing: a rated glaze on any surface that touches food or lips, anything you like on the outside, and no crazed pot in the cupboard.

What the labels actually mean

Food safe, dinnerware safe and non-toxic are three different promises, and the difference matters on a mug.

Food safe symbol as it appears on a glaze bottle

Food safe

A wine glass and fork on the bottle. In the United States this label has a legal definition behind it: the FDA sets limits on how much lead and cadmium a fired glaze may release, in Compliance Policy Guides 545.450 and 545.400, measured by the ASTM C738 leach test.

What it promises is narrow and specific. Used as the maker directs, the glaze will not leach harmful lead or cadmium into your food. That is the whole claim.

What it does not promise is durability. A food safe glaze can still craze, scratch, stain or fail in a dishwasher. Safe to eat from is not the same as built to last.

Dinnerware safe symbol as it appears on a glaze bottle

Dinnerware safe

A step beyond food safe. The glaze has to be non-leaching and also smooth, hard and non-absorbent, with nowhere for bacteria to sit.

The FDA Food Code asks food contact surfaces to be safe, durable, corrosion resistant, heavy enough to survive repeated washing, smooth and easily cleanable, and resistant to pitting, chipping, crazing, scratching and distortion. That is a much higher bar than a leach test.

And it is specific to the clay underneath. A glaze can only be called dinnerware safe on a body it has been tested against, because a thermal expansion mismatch causes crazing, and crazing disqualifies it whatever the jar says.

Non-toxic

The most misread label on the shelf. Non-toxic describes the wet glaze in the jar, not the fired surface on your pot.

It means the material will not harm you in normal use: handling it, brushing it, working near it. Think safe to touch rather than safe to eat from.

A glaze can be genuinely non-toxic and completely wrong for the inside of a mug. If a bottle says non-toxic and nothing else, treat it as decorative until you find a food safe statement.

Dishwasher and microwave safe

Separate claims again, and separate from food safety. A glaze can be food safe and still come out of a dishwasher dulled, or develop crazing after enough heat cycles.

Microwave safe usually fails for one of two reasons: metallic content in the glaze, or a body that absorbs water and heats unevenly. Anything with real metal in it stays out of the microwave regardless of what else the label says.

Check each glaze page. We record these separately because the makers do.

AP and CL seals

Two seals from the art materials world, answering a different question than the FDA does.

AP means Approved Product. A toxicologist reviewed the formula and found no ingredient in a quantity likely to cause acute or chronic harm, including to children. The closest thing to a safe for all ages stamp.

CL means Cautionary Labeling. A toxicologist reviewed it, found something worth warning about, and required that warning to be printed. Generally not for anyone under 12. Neither seal says anything about whether the fired glaze is safe for food.

ASTM C-1023 and D-4236

Two standards you will see in small type. C-1023 covers labeling ceramic art materials for chronic health hazards, D-4236 covers art materials generally.

Worth knowing what they actually do: they require a manufacturer to disclose known risks. They do not define tests for chronic hazards, they are written for artist-sized quantities rather than industrial use, and they do not claim to cover every concern.

They are a disclosure framework, not a guarantee. The last line of defense is still the person holding the brush.

Dinnerware safe with a clear glaze symbol as it appears on a glaze bottle

Dinnerware safe with a clear glaze

A spoon and fork with a spark beside them. It means the glaze is not dinnerware safe on its own, but becomes so once a food safe clear goes over it.

Most underglazes sit here. The color is stable, the surface is not, and a clear coat does the sealing. Skip the clear and you have a decorative pot.

If you are underglazing the inside of a mug, the clear is not optional.

Not dinnerware safe symbol as it appears on a glaze bottle

Not dinnerware safe

The same spoon and fork, crossed out. This one is unambiguous and worth taking at face value.

It does not mean the glaze is dangerous to handle or that you cannot use it. It means the fired surface has no business touching food, at any thickness, with any clear over it.

Put it on the outside, keep it off the rim, and line the inside with something rated.

The liner rule, and why it solves almost everything

You do not have to choose between a safe pot and an interesting one. Glaze the inside with a proven liner and the outside with whatever you like, and you get both.

That one habit removes most of the risk from most of the shelf. The wild reactive on the outside never touches coffee, the tested white inside does all the work, and the line where they meet at the rim reads as a deliberate design decision rather than a compromise.

We stock two liners for exactly this, a gloss and a satin white.

Three labels, three different promises

These three get used as though they mean the same thing, and they do not. Non-toxic is about the wet glaze in your hand. Food safe is about what the fired surface releases. Dinnerware safe is about whether the finished pot holds up in real use, on the clay you actually used.

A glaze can carry the first and fail the other two. That is not a loophole. It is three separate questions answered by three separate tests.

Much of the detail on this page follows the Ceramic Materials Workshop guide to glaze labels, which is the clearest public explanation of these standards we know of.

Common questions

Does food safe mean the maker guarantees my pot?

No. It means the recipe tested sound. Your clay, your thickness and your firing are still yours.

What is crazing and why does it matter?

A fine web of cracks in the glaze. It gives bacteria a home and lets liquid reach the clay, and it voids a food safe rating no matter what the jar says.

Can I put a decorative glaze on the outside of a mug?

Usually yes, if the inside and rim are a rated glaze. Check the glaze page, because a few run onto surfaces you did not intend.

Are these dishwasher safe?

Follow each glaze page. Dishwasher and microwave ratings are separate from food safety and not always the same answer.

Why is a glaze I use all the time not in the first group?

Either its maker gave a narrower rating than you expect, or its notes do not state one clearly. The glaze page has the full wording.

What about raku?

Never food safe, and it is not on this page. Raku has its own collection.

Simplest safe habit?

Rated glaze on anything that touches food or lips, anything you like on the outside.

The short version: a liner inside, whatever you want outside, and no crazed pot in the cupboard.

Also worth a look

Studio FavoritesThe glazes we keep coming back to, chosen on behavior rather than looks. Metallic GlazesMetal rather than glass. Spectacular when they land, and the least forgiving glazes we stock. Good for TextureThe glazes that show your carving instead of filling it in.
Back to the Glaze Bible
About these images and what your pot will actually look like

We have done our best to represent every glaze here accurately, and you should still expect your pot to look different from what is on this screen.

Our glaze tile images are digitally created. They are built to show the character of a glaze, not to be a color match.

A screen is not a printout, a printout is not a test tile, and a test tile is not a finished pot. Each step in that chain shifts what a glaze looks like, sometimes a lot.

On top of that, the pottery itself changes the result: the clay body, how thick the glaze went on, whether it was brushed, dipped or sprayed, what was layered under or over it, where the piece sat in the kiln, how hot that spot ran, how fast it cooled, what was fired next to it, and how much texture the surface had. Two pots glazed from the same jar on the same day can come out different.

Treat every image here as a starting point, and treat a test tile fired on your own clay as the real answer.

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