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 our glazes are tested by their makers, which is a good foundation; 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.
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 lemon slice lifted off a tile the next morning, or a mug in a microwave next to a cup of water, and those are the videos, from potters who sell functional ware and have answered this question more times than they would like.
Use both, in this order
Read what each claim commits you to. Watch the two home tests. 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 colourant inside. Dishwasher safe adds no lustre. 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.
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 unglazed scrap of your clay, a tile of every liner glaze, a lemon, a microwave and a cup of water, the glaze company’s label, and a label with your name on it.
Step one
Food safe: a vitrified body, a fitted glaze, no crazing, no raw colour 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 does not absorb; 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 eight clay bodies fire vitrified, and the 650+ brush-on glazes and seven dipping buckets are commercial glazes made by companies that test them. That is the foundation, and it is a good one. 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. The jar’s label is 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, the stoneware does not, and absorption is where the trouble lives. Our glaze problems lesson is the crazing half.
Step two
Dishwasher and microwave: the same, plus no lustre and no metal, plus even walls.
Dishwasher safe adds one thing; microwave safe adds three. A vitrified body with a fitted uncrazed glaze survives a dishwasher indefinitely; the exception is a lustre 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 holds no water.
What fails
Crazed glazes, which absorb and stain. Unglazed surfaces on porous bodies. Gold and silver lustres and most metallic glazes, which wear. Everything else on a vitrified stoneware at cone 5½ is fine, and dishwasher safe is a claim most pots here can carry once they have been checked for crazing.
What fails
Anything with metal: lustres, 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.
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 almost nothing. 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 lab leach test on a tile costs less than a bad review. What the home tests give you is the right to write the claim on the pots you make with that glaze on that clay fired that way, and the good sense not to write it on the ones that failed. Tammy Jo Schoppet’s video below shows the lemon and the soak at a kitchen table.
Then the tile goes in the drawer with the result written on the back, 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, against a legal limit, and it is what a shop or a wholesale buyer may ask for. It is a tile posted to a lab and a small fee, and for a potter selling liner-glazed ware in volume it is cheaper than a single bad week. For a member selling twelve mugs at a market, the lemon and the honest label are the right amount of care.
Step four
Write only what passed, and put your name on it.
The claim is the maker’s. 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: the glaze that passed the lemon, the body that passed the soak, the 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 lustred 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 on food safe against dinnerware safe is the distinction: the jar can be labelled 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 lustred 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. The claim is about the surface food touches, and every other surface is yours to do anything with.
Watch it done
Now watch four people answer the question.
Watch this one, then go buy a lemon.
None of these potters work here or know we exist. Between them they cover vitrification as the whole story, the two home tests, the long careful version, and food safe against dinnerware safe. Nothing but the still frame loads until you press play.
Thirteen minutes on why a vitrified body with a fitted glaze is what every claim rests on. The other three videos are in the comprehensive version.
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 colour, the lemon, and whose name is on it.
You wrote food safe on a pot with a crazed glaze
Crazing is a network of cracks that hold coffee and bacteria and cannot be cleaned. On a vitrified body the pot does not weep, but the claim is about the surface, and the surface is cracked.
No claim on a crazed pot. Sell it as decorative, keep it for dry things, or do not sell it. Fix the pairing per the glaze problems lesson.
Take the label off. A crazed mug is a pencil pot.
You wrote microwave safe on a pot with a lustre or a metallic glaze
Gold lustre, silver, and some metallic and bronze glazes carry real metal. In a microwave they arc, spark and can crack the pot.
Nothing with a lustre or a metallic glaze carries a microwave claim. Test one in a microwave for thirty seconds with a cup of water beside it before deciding about a glaze you are unsure of.
Reprint without the microwave claim. The dishwasher claim may still stand; the lustre lesson covers which.
A thick pot cracked in a microwave or an oven
Uneven thickness heats unevenly. A pot with a thick base and thin walls, or a glaze on one side only, expands at two rates and cracks. An oven does it faster.
Even walls, even glaze, and no oven claim on anything not designed for it. Microwave safe is a reasonable claim for a thin, even, vitrified pot with a fitted glaze and no metal; oven safe is a claim most potters never make.
Drop the oven claim entirely. Keep the microwave claim for pots you have tested.
A raw oxide wash or an unglazed stained surface is on the inside of a bowl
Raw oxides and stains without a fitted glaze over them can leach. Cobalt, chrome, copper and manganese in a wash on a food surface with no clear over them are not a food-safe surface.
A fitted clear glaze over every wash and every stained surface on the inside of anything that holds food or drink. Outside surfaces can be whatever you like.
Reglaze the inside with a clear and refire. Or sell it as a planter.
A glaze changed colour under a lemon slice overnight
Acid pulled something out of the glaze. A glaze that changes colour or texture under lemon or vinegar is leaching, and it does not carry a food claim on that pot.
Test a tile of every glaze you use on food surfaces with a lemon slice overnight. A glaze that passes on a tile and is fired the same way on a pot is a glaze you can stand behind.
No food claim on that pot with that glaze. Try a different liner glaze for the inside.
You wrote The Clay Hole on the label as if it were the guarantee
The studio fires the pot; it does not certify it. The claim on a label is the maker’s, and a stranger holds the maker to it.
Your name on the label, your test on the glaze, and a claim you can stand behind. The studio’s name is where it was made, not who is promising.
Reprint with your name and your claim.
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, so you know before you start.
Three things to know here
Our eight clay bodies fire vitrified at cone 5½, and every glaze on the wall and in the buckets is a commercial glaze tested and labelled by its maker. 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. All eight of our clay bodies fire vitrified at it, which is the absorption half of every claim on this page done for you. A pot made from our clay and fired here starts from a vitrified body.
The glazes
650+ brush-on glazes and seven dipping buckets, all commercial, all tested and labelled by the companies that make them, all fired here every week. The jar’s label is 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
Oxides and stains are bring-your-own here, and a raw wash 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 colourant without a fitted glaze over it, and no lustre 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 survives a dishwasher indefinitely; the water cannot get in and the glaze does not soften. Earthenware, unglazed surfaces and crazed glazes absorb water and slowly deteriorate. Lustres and some metallic finishes wear off. At cone 5½ on our bodies with a commercial glaze that fits, dishwasher safe is a claim most pots can carry; the exceptions are the crazed ones and the lustred ones.
Microwave safe?
No metal in or on the pot, no lustre, even walls, an uncrazed fitted glaze, and a vitrified body that does not hold 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?
Two tests. Absorption: weigh a fired, unglazed scrap of the clay, soak it overnight, weigh it again; a vitrified body gains almost nothing. Leaching: a lemon slice face down on the glazed surface overnight, and any change in colour or texture where the lemon sat is a glaze that leaches on that pot. Neither is a laboratory test, and both are what a careful potter does before writing anything on a label. Tammy Jo Schoppet’s video below shows both.
Are our glazes food safe?
The commercial glazes on the wall are made by companies that test them and label them, and 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 jar’s label 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. Most pots most members make can carry most 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.
That is the whole page
Vitrified body. Fitted glaze. No crazing. Clear over colour. 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. Most pots most members make can carry most 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.
Written for potters everywhere. Where our studio does things differently, the page says so.
Which version would you like to print?
Both print clean, with the videos turned into labelled boxes you can search for later.