Selling your work · Food safe and what you can claim

Four claims people make casually, and what each one actually commits you to.

Food safe, dishwasher safe, microwave safe, oven safe. Each is a promise about one specific pot to a stranger who will hold you to it. Our bodies fire vitrified at cone 5½ and the Food Safe Lookup records which of our glazes their makers rate for food, which are only cleared, and which must never touch food; the pairing, the thickness, the crazing and the claim are yours.

Four steps with a tick list at each: what food safe takes, what dishwasher and microwave add, the three home tests, and the label. Six mistakes, most of them a claim written before it was checked, and four videos.

This is the short version: what each claim takes, the three tests, and the label, each with a tick list. The reasoning, the oven note and the questions are in the comprehensive version.

x4Claims. Each a promise about one pot
Cone 5½Our bodies fire vitrified at it. The foundation, not the claim
x4Videos, from makers and a supplier we do not work with
x4Steps, each with a tick list you can work off
Jump to a section
Why this page has words and video The whole idea in three lines The claims in six moves What you need to test 1. Food safe 2. Dishwasher and microwave 3. The tests 4. The label Four videos, four claims The one video to watch When it goes wrong How it works at The Clay Hole Questions people actually ask Related lessons
An illustrated potter with purple hair and glasses, in a clay-stained apron, loading mugs and bowls into an open dishwasher in a studio kitchen

Every claim in full, the oven note, the lab-test note and four videos.

Read it, then watch it

Why this is written down and filmed, both.

Four claims people write casually, and each one is a promise about a specific pot to a stranger. What each promise commits you to is a list, and a list belongs on a page you can read with the label in your other hand. What a page cannot show is a person explaining it out loud, and that is what the videos are for, from makers and a supplier who have nothing to do with us.

Use both, in this order

Read what each claim commits you to. Watch the four videos. Test every glaze you use on a food surface, once, on a tile. Then write only what passed.

The whole idea

Four claims, each a promise about one pot, and every one of them is yours.

Food safe means a vitrified body, a stable fitted glaze, no crazing, no raw colorant inside. Dishwasher safe adds no luster. Microwave safe adds no metal and even walls. Oven safe is a claim most potters never make. Test the glaze on a tile with a lemon, write what passed, and put your name on it, not the studio’s.

The five-minute version

The four claims in six moves.

If you already sell and you just want the shape of it, this is the shape of it. Everything below is these six moves, slowed down and with the places they fail marked.

1Vitrified body, fitted glazeAt cone 5½ our bodies fire vitrified. A fitted, uncrazed commercial glaze over it is the foundation of every claim.
2No crazing, everA crazed surface holds coffee and bacteria. No claim on a crazed pot, whatever the body.
3Clear over every wash insideRaw oxides and stains on a food surface get a fitted clear glaze over them, or the pot is a planter.
4No luster, no metal, for dishwasher and microwaveGold, silver and metallic glazes wear in a dishwasher and arc in a microwave. Those pots carry neither claim.
5Test on a tile: lemon overnight, absorption, microwaveEvery glaze you use inside a pot, once. Write down what passed.
6Your name, your claimThe studio fires it; the company made the glaze; the claim on the label is yours.

Before you print a label

What you need to test.

Six things, and one of them is a lemon. The label with your name on it is the whole point.

A fired scrap of your clay, unglazedFor the absorption test: weighed, soaked overnight, weighed again.
A tile of every food-surface glazeFired at cone 5½ on your clay, on a kiln cookie. The studio team loads every kiln, so ask them to put the tile in with your pots.
A lemonSliced, face down on the glazed tile overnight. Any change where it sat is leaching.
A microwave and a cup of waterThirty seconds, the pot beside the cup. If the pot is hotter than the water, no microwave claim.
The jar’s label and the Food Safe LookupThe jar says what the glaze was made for. The Food Safe Lookup says whether it is rated for food, only cleared, outside only or never for food.
A label with your name on itThe claim is yours. Not the studio’s and not the glaze company’s.

A fired unglazed scrap of your clay, a tile of every liner glaze, a lemon, a microwave and a cup of water, the jar’s label and the Food Safe Lookup, and a label with your name on it.

1

Step one

Food safe: a vitrified body, a fitted glaze, no crazing, no raw color inside.

Food safe is a claim about a surface. The surface food touches will not put anything harmful into it and can be cleaned. Four things: a vitrified body, so it absorbs very little; a stable glaze fired as it was made to be; no crazing, because cracks hold coffee and bacteria; and no raw oxide or stain inside without a fitted glaze over it.

At cone 5½ our clay bodies fire vitrified, and the 650+ brush-on glazes and our dipping buckets are commercial glazes, and the Food Safe Lookup records which of them are rated for food, which are only cleared, which are for the outside of a pot only and which must never touch food. That is where a claim starts. But a glaze in a jar is not a pot. The same glaze fired too thin is a different surface; too thick, another; crazed on one body and fine on another, a third; over a cobalt wash with no clear, a fourth. Lead free does not mean food safe, and bright reds and oranges can carry cadmium locked inside a stain that only holds up to a certain heat, so keep those off food surfaces unless the Food Safe Lookup clears the glaze. The jar’s label and the Lookup are where the claim starts, and the pot is where it ends.

Unglazed earthenware is treated differently from vitrified stoneware for one reason: the earthenware absorbs a lot, the stoneware very little, and absorption is where the trouble lives. Our glaze problems lesson is the crazing half.

Tick list, food safe0 of 4
2

Step two

Dishwasher and microwave: the same, plus no luster and no metal, plus even walls.

Dishwasher safe adds one thing; microwave safe adds three. A vitrified body with a fitted uncrazed glaze holds up well in a dishwasher; the exception is a luster or a metallic finish, which wears off. Microwave safe needs all of that, plus no metal on the pot, walls even enough to heat at one rate, and a body that takes in very little water.

Dishwasher

What fails

Crazed glazes, which absorb and stain. Unglazed surfaces on porous bodies. Gold and silver lusters and most metallic glazes, which wear. Check everything else against the glaze’s page in the Food Safe Lookup, which records dishwasher and microwave separately. Dishwasher safe is a claim to make glaze by glaze, and only once the pot has been checked for crazing.

Microwave

What fails

Anything with metal: lusters, metallic and bronze glazes, which arc. Thick bases with thin walls, which heat unevenly and crack. Crazed or porous pots, which hold water that turns to steam. A thin, even, vitrified mug with a plain fitted glaze heats fine; test it with a cup of water beside it and compare temperatures.

Oven safe is the fourth claim, and it is the one most potters never make. It needs a form designed for the oven, even walls, no sharp corners, a body that tolerates thermal shock, and instructions about preheating; a mug nobody designed for an oven is not oven safe because it survived one. Leave it off unless you made the pot for the oven and tested it there.

Tick list, dishwasher and microwave0 of 3
3

Step three

Test on a tile: a lemon overnight, a soak, and thirty seconds in a microwave.

Three home tests, once per glaze, before anything is printed. Leaching: a lemon slice face down on the glazed tile overnight; any change where it sat is a glaze that leaches. Absorption: a fired unglazed scrap, weighed, soaked overnight, weighed again; a vitrified body gains only a small amount. Microwave: a glazed cup beside a cup of water for thirty seconds; if the pot is hotter, it is absorbing energy.

None of these is a laboratory test, and a potter selling in volume or into a shop may want a laboratory one; a laboratory leach test is the next step up. What the home tests give you is a way to catch a glaze that fails, and the good sense not to write the claim on a pot whose tile changed. No change is not proof that a glaze is safe. The Hobby Potter video below covers absorption and leaching tests.

Then log the result against the tile’s number, per our test tiles lesson, and the glaze goes on the inside of pots or does not. A glaze that fails as a liner is often a fine glaze for the outside of the same pot, where nothing is eaten off it.

What a laboratory test adds

A lemon on a tile tells you whether a glaze visibly changes under acid. A laboratory leach test tells you what came out and how much, and it is what a shop or a wholesale buyer may ask for. A lab prices it metal by metal, and only lead and cadmium have legal limits in ceramicware, so a full palette adds up. For a member selling twelve mugs at a market, start with the Food Safe Lookup, use a lemon on a tile to catch a failure, and write an honest label.

Tick list, the tests0 of 4
4

Step four

Write only what passed, and put your name on it.

The claim is yours. The studio fires the pot; the glaze company tests its glaze in its lab; neither is standing behind the mug in a stranger’s hands. You are. So the label carries your name and only the claims that pot has earned: a glaze the Food Safe Lookup rates for food, a body that soaked up little, a mug that stayed cooler than the water.

Say it plainly and specifically. Dishwasher safe. Microwave safe. Food safe glaze on a vitrified stoneware. Hand wash only, for the lustered one. Not for the oven. A label that says less and means it is worth more than one that says everything and hopes. Blick’s ninety seconds below touch on food safe against dinnerware safe glazes. The jar can be labeled food safe and the pot still has to earn it.

And the pots that did not pass are not wasted. A crazed mug is a pencil pot, a lustered bowl is a hand-wash bowl, a bowl with a raw wash inside is a planter, and a glaze that leached as a liner is a good glaze for an outside, kept off the rim. The claim is about the surface food touches, and the rim your lips touch is part of it; every other surface is yours to do anything with.

Tick list, the label0 of 4

Watch it done

Now watch four people answer the question.

Watch this one, then go buy a lemon.

None of these people work here or know we exist. Between them they cover vitrification and the three claims, absorption and leaching tests, a long walk through food safe pottery, and food safe against dinnerware safe glazes. Nothing but the still frame loads until you press play.

Thirteen minutes on how vitrification relates to food safe, microwave safe and dishwasher safe pottery. The other three videos are in the comprehensive version.

Vitrification and the three claims How to make pottery Food Safe, Microwave Safe, & Dishwasher Safe // It's all about Vitrification! Pottery to the People
Thirteen minutes on how vitrification relates to food safe, microwave safe and dishwasher safe pottery, with chapters on testing for porosity and on crackle glazes. Watch on YouTube
Absorption and leaching tests Is Your Pottery Food Safe? Absorption & Leaching Test Explained Hobby Potter
Six minutes, a short segment from a workshop, in which the maker tests ceramics for absorption and leaching. The description points to written directions online. Watch on YouTube
The long version 95. Food Safe Pottery - How to make Pottery Food Safe Mikkel deMib
Sixteen minutes in chapters on what food safe pottery means, how it is tested, glazes and how they are applied, unglazed ware, sealing and pit fired pottery. The maker takes a relaxed view of the risk, so check any glaze in the Food Safe Lookup before you rely on it. Watch on YouTube
Food safe against dinnerware safe Understanding Ceramic Glazes: Low-Fire vs High-Fire and Food-Safe vs Dinnerware-Safe Blick Art Materials
Ninety seconds from a supplier on low-fire and high-fire glazes, ending with food safe against dinnerware safe glazes. Watch on YouTube

When it goes wrong

Six ways it goes wrong, and what to do about each.

The three claims most often written before they were checked.

Pick the one that looks like your label. The first three are crazing, metal and thickness. The last three are raw color, the lemon, and whose name is on it.

Pick the one that looks like your label. They are crazing, metal and thickness.

How it works here

At The Clay Hole, the firing is the foundation and the claim is yours.

This page is written for potters everywhere. A few things are specific to our building.

Three things to know here

Our clay bodies fire vitrified at cone 5½, and every glaze on the wall and in the buckets is a commercial glaze, and the Food Safe Lookup says which are rated for food and which never touch it. That is the foundation. A glaze in a jar is still not a pot: thickness, pairing and crazing are yours to check, and the claim on the label is yours, not the studio’s.

The firing

Cone 5½, the same every load. Every one of our clay bodies fires vitrified at it, which is a good start on the absorption half of every claim on this page. A pot made from our clay and fired here starts from a vitrified body.

The glazes

650+ brush-on glazes and our dipping buckets, all commercial, and the Food Safe Lookup records which are rated for food, which are only cleared, which are for the outside only and which must never touch food. Raku glazes are never food safe. The jar’s label and the Lookup are where your claim starts. The pairing with your clay, the thickness and the crazing are yours to check on a tile.

Washes, stains and outside materials

A raw wash or stain on a food surface with no clear over it is not a food-safe surface whoever fired it. A fitted clear over every wash inside anything that holds food or drink, and tell the studio team before anything you bring in goes into a kiln.

Whose claim

The studio fires your pot; it does not certify it. The studio’s name on a label is where the pot was made, not who is promising. Your name, your tests, your claim, and our selling lesson for the rest of the label.

Questions people actually ask

The ones that come up every week.

What does food safe actually mean?

That the surface a food or drink touches will not put anything harmful into it, and can be cleaned. In practice: a vitrified clay body, a glaze that has been formulated and fired to be stable, no crazing, no raw colorant without a fitted glaze over it, and no luster on the food surface. It is a claim about a specific pot, not about a glaze in a jar, because the same glaze fired too thin, too thick or on the wrong clay is a different surface.

Dishwasher safe?

A vitrified stoneware with a fitted, uncrazed glaze holds up well in a dishwasher; very little water gets in and the glaze should not soften. Earthenware, unglazed surfaces and crazed glazes absorb water and slowly deteriorate. Lusters and some metallic finishes wear off. At cone 5½ on our bodies, dishwasher safe is a claim to make glaze by glaze: check the glaze’s page in the Food Safe Lookup, which records dishwasher and microwave separately. The crazed ones and the lustered ones never carry it.

Microwave safe?

No metal in or on the pot, no luster, even walls, an uncrazed fitted glaze, and a vitrified body that takes in very little water. A thin, even mug ticks all of those and heats fine. A thick-bottomed pot, a crazed one, or one with a metallic glaze does not. Test every glaze you are unsure of: thirty seconds in a microwave with a cup of water beside it, and if the pot is hotter than the water, it is absorbing energy and should not carry the claim.

Oven safe?

Most potters never make this claim, and the ones who do make it for specific forms designed for it: even walls, no sharp corners, a body that tolerates thermal shock, and instructions about preheating. A stoneware mug is not oven safe because nobody designed it to be. Leave this claim off unless you have made the pot for the oven and tested it there.

How do I test at home?

Three tests. Absorption: weigh a fired, unglazed scrap of the clay, soak it overnight, weigh it again; a vitrified body gains only a small amount. Leaching: a lemon slice face down on the glazed surface overnight, and any change in color or texture where the lemon sat is a glaze that leaches on that pot. Microwave: thirty seconds with a cup of water beside it, and if the pot is hotter than the water, no microwave claim. None is a laboratory test, and all three are what a careful potter does before writing anything on a label. The Hobby Potter video above covers absorption and leaching tests.

Are our glazes food safe?

Some are and some are not. Check each glaze in the Food Safe Lookup (theclayhole.com/pages/glaze-collections/food-safe-glazes): some are rated for food by their maker, some are only cleared, some are for the outside only and some must never touch food. At cone 5½ on our bodies they fire as intended. But a glaze in a jar is not a pot: the same glaze too thin, too thick, crazed on one of our bodies, or over a raw wash is a different surface. The Food Safe Lookup is where you start. The claim on your pot is yours, and it rests on the pairing, the application and the firing, which is why the test tile matters.

Whose claim is it?

Yours. The studio fires your pot at cone 5½ on our schedule; the glaze company tests its glaze in its lab; neither of them is standing behind the mug in a stranger’s hands. Test the glaze, check the pot, write what you can stand behind, and put your name on it. Many pots can carry some of these claims, once checked; the checking is the job.

Related lessons

Six lessons that sit next to this one.

Three to read next.

A claim rests on the firing, the glaze fit and the test tile. These are those pages.

GlazingGlaze Problems, Causes and FixesCrazing, which is the claim-killer, and why it is a fit problem. GlazingTest TilesHow to make, number and log a tile for every glaze. Selling your workHow to Start Selling Your PotteryThe label, and everything else on it. Surface and decorationUsing Mason StainsThe colorants, and the clear that goes over them. Firing and fixingWhat a Firing Actually DoesWhat happens to the clay and the glaze in each firing. FoundationsThe Many Myths of PotteryIncluding several about what is and is not safe.

That is the whole page

Vitrified body. Fitted glaze. No crazing. Clear over color. No metal. Test it. Your name.

Your first label will say everything, and a crazed mug will go out under it, and you will get an email. That is normal, and the second label will say less and mean it. Many pots can carry some of these claims, once checked. The checking is the job, and a lemon costs a dollar.

If you want the reasoning, the oven note, the lab-test note and the answers to the questions everybody asks, switch to the comprehensive version at the top. Otherwise, go put a lemon on a tile.

Back to Clay Hole University Crazing, the claim-killer

Written for potters everywhere. Where our studio does things differently, the page says so.