Surface and decoration · Using mason stains
One jar of powder colours clay, slip, engobe or glaze.
A stain is colour that has already been fired, so what is in the jar is close to what comes out of the kiln. The percentage changes for each thing it goes into, the note on the jar decides which glaze it survives in, and a test tile decides everything else.
Four steps with a tick list at each: the four uses and their percentages, weighing and wetting, wedging or sieving until it is even, and the test tile. Six fixes, six videos, and the safety rule that opens every jar.
This is the short version: the four percentages, the mask, the paste, the sieve and the tile, each with a tick list. The chemistry, the food-safety notes and the questions are in the comprehensive version.
Read it, then watch it
Why this is written down and filmed, both.
Stains are a table of percentages with a compatibility note attached, and tables are what a page is for. Five to ten in clay, five to fifteen in slip, two to ten in glaze, a wash at half and half. Nobody remembers those from a video. What a page cannot show is a paste being wedged into clay until the streaks vanish, or a sieve being worked, and those are the videos. Six of them, because stains have five uses and one safety lesson.
Use both, in this order
Read the percentages and the compatibility note for your colour. Watch the use you want. Mix a test tile before a pot, every time, with the tick list open.
The whole idea
One jar of fired pigment, four percentages, one test tile.
A stain is colour that has already been fired, so what is in the jar is what comes out of the kiln. Five to ten percent colours a clay body, five to fifteen a slip or engobe, two to ten a glaze, half and half with water makes a wash. Wet the powder first, sieve or wedge it in, read the note on the jar, fire a tile before a pot. Mask on whenever the jar is open.
The five-minute version
The whole technique in six moves.
If you already mix slips or glazes 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 open the jar
What you need on the bench.
Six things, and the mask is not optional. The sieve is the one people skip and then wonder about the speckles.
A jar of stain, a scale, a mask and gloves, an 80 mesh sieve, the clay, slip or glaze it is going into, and test tiles.
Step one
Decide what the stain is going into, and read the note on the jar.
One powder, four jobs, four percentages. Into a clay body it colours the clay through. Into a slip or an engobe it colours a coating. Into a glaze it colours the glass. With water it is a wash for wiping into texture. The percentage is different for each.
Clay body
Of the dry clay weight, up to fifteen for weak colours. The colour runs through the pot, shows on every trimmed edge and every carved line, and survives anything. Past fifteen the clay goes short and cracks. Strong stains, cobalt blues and blacks, want the low end.
Slip and engobe
Of the dry weight of the slip. The cheapest way to a hundred colours from one bucket of slip and a few jars, and the way to match a colour to your own clay body. This is what underglaze is, before somebody bottled it. Our engobes lesson is the coating side.
Glaze
Of the dry glaze weight, most colours between two and six. Stain stiffens a glaze, so the top of the range changes the fit. The base glaze has to suit the stain: read the compatibility note first.
Wash
Roughly equal parts stain and water, with a spoon of the base glaze or a frit so it sticks, brushed on and wiped back so only the texture keeps it. A clear over the top on anything that touches food. Our wipe-away lesson is the method.
Then the note on the jar, which is the part beginners skip and regret. Chrome-tin pinks and maroons need calcium in the glaze and die with zinc. Some blues and greens are happy anywhere. Encapsulated reds, oranges and yellows fade if fired past their limit. The supplier’s chart lists a compatibility note for every colour, and a stain in the wrong base fires out to grey.
Step two
Mask on. Weigh it dry, then wet it to a paste.
The jar does not open without a mask. Stain is ground metal oxide fused into a glass and ground again, safer than raw oxide and still not for lungs. A fitted respirator or a good mask, gloves, a damp towel under the scale, never at a shared table.
Weigh by dry weight. For clay, that means the dry weight of the clay, which for soft clay from the bag is roughly three quarters of what the scale says; for a pound of soft clay, about a twelve ounce dry weight, so ten percent is a little over an ounce of stain. For slip and glaze, weigh the dry materials before the water goes in, or work from the recipe. Write the numbers down; you will want to repeat the good one.
Then wet it. A spoon of water stirred into the weighed powder until it is a smooth paste with no dry pockets. Dry stain dropped into wet clay or slip clumps, and every clump is a speck on the pot. The paste is the whole difference between an even colour and a marbled one.
Step three
Mix it in until it is even. Wedge, or sieve.
Stain does not dissolve. It has to be spread. Into clay: spread the paste on softened clay, fold it in, wedge far longer than feels necessary, then cut the lump in half and look. Streaks mean more wedging. Into slip, engobe or glaze: stir the paste in, then sieve through 80 mesh, glaze twice.
A marbled lump is not a failure if you wanted marbled clay, and some potters stop wedging on purpose at the streaky stage. For an even body, keep going. Stained clay is also a good candidate for a second wedge the next day, after it has rested and evened out its moisture. Our wedging lesson is the method.
Keep stained clay separate from everything: its own bag, its own name, its own reclaim. A scrap of cobalt-stained clay in the studio reclaim is a blue speck in somebody else’s bowl months later. Stained slip and glaze go in labelled containers with the percentage and the base written on the lid.
Step four
Fire a tile before a pot. Then use it.
The tile is the recipe. One test tile per colour per base, fired at cone 5½ under the glaze you mean to use, with the percentage and the base written on the back in underglaze. A stained body wants a tile with a carved line and a clear over half of it. A stained slip wants a tile of your clay with the slip on it. A stained glaze wants the glaze on the clay it will live on.
Then use it the way the tile told you. A stained body throws, hand-builds and trims like the clay it came from and shows its colour on every cut edge, which is why potters carve it. A stained slip or engobe goes on leather hard for a surface that fires like clay, or bisque for engobe, and takes sgraffito beautifully. A stained glaze is a glaze, with the fit the tile showed. A wash wipes into texture and wants a clear over it on anything that touches food.
Food safety follows the glaze, not the stain: a stained body or a wash under a fitted clear is as safe as the clear. Bare stained clay on a food surface is not settled, and chrome and cobalt stains especially want covering. When in doubt, a coat of clear, which is the answer to most glaze questions.
Watch it done
Now watch six people use one jar five ways.
Watch this one, then go read the note on the jar.
None of these potters work here or know we exist. Between them they cover what a stain is against an oxide, stain into clay twice, stain as a wash, stained slip against bought underglaze, and the compatibility notes explained. Nothing but the still frame loads until you press play.
Seventeen minutes from a teacher on what a stain is, why it is predictable, and how much goes in. The other five videos are in the comprehensive version.
When it goes wrong
Six ways it goes wrong, and what to do about each.
The three failures that happen on the first tile.
Pick the one that looks like your tile. The first three are chemistry and mixing. The last three are percentage, fit and your lungs.
The colour fired out or went muddy
The stain met a glaze it is not compatible with, or too little went in, or it was fired past its limit. Chrome-tin pinks die without calcium and with zinc; some yellows and oranges are encapsulated and fade if overfired; a stain at two percent in a glaze is a tint, not a colour.
Read the note on the jar or the supplier’s chart before choosing a base. Use the middle of the percentage range, not the bottom. Test on a tile at cone 5½ before a pot.
A faded pot is a pale pot. On the next tile, double the percentage or change the base glaze, one variable at a time.
Speckles, streaks or marbling where you wanted an even colour
Dry stain went into wet clay or slip without being wetted first, so it clumped, or the clay was not wedged enough to distribute it. Stain does not dissolve; it has to be spread.
Wet the stain to a paste with a little water first, work the paste into soft clay, and wedge fifty times more than feels necessary. For slip, sieve the mix through an 80 mesh sieve.
If it is still soft, keep wedging. If it is fired, you have marbled clay, which some people pay for. Cut the clay in half to see if it is even before you commit it to a pot.
The colour bled or blurred into the glaze over it
A stain wash was put on too thick, or the glaze over it was too thin, or the stain is a strong colourant like a cobalt blue that moves in a melt.
Wash thin, wiped back so only the texture holds it. A full coat of clear over the top. Fire a tile of the wash under the glaze you mean to use.
Fired is fired, and a soft bleed under a clear often reads as depth. The next one is thinner.
The stained clay is short, cracks when bent, and dusts
Too much stain. Stain is a ground, fired pigment with no plasticity, and past about fifteen percent a clay body stops being clay.
Five to ten percent by dry weight for most colours, fifteen for the weak ones, never more. Colour the surface with a stained slip or engobe instead and leave the body alone.
Wedge in plain clay to bring the percentage down. If it is already a pot, it is a fragile pot.
A glaze with stain in it crawled, crazed or went matte
Ten percent of anything added to a glaze changes the glaze. Stain is a refractory powder; enough of it stiffens the melt, and some stains pull the glaze off the pot in a crawl.
Stay under ten percent in glaze, most colours want two to six. Sieve the mix. Test on a tile, both the colour and the fit, before it goes near a pot.
A crawled test tile is a cheap lesson. A crawled pot is a cheap lesson with a pot attached.
You breathed it
Stain powder is finely ground metal oxides fused into a glass and ground again. It is safer than raw oxides and still not for lungs. Cobalt, chrome and nickel stains are the ones to respect most.
A fitted respirator or at least a good mask whenever the jar is open. Weigh over a damp paper towel. Wet it before mixing. Wipe the bench down wet. Never at a shared table.
Close the jar, wipe everything down wet, and do the rest of the job with the mask on.
How it works here
At The Clay Hole, stains are bring-your-own and the reclaim is sacred.
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
Stains are bring-your-own; we do not stock them. Colouring a batch of our clay with your stain is fine; as with anything you bring in that will go into a kiln, tell the studio team first. Mix away from the shared tables with a mask on, and keep stained clay in its own bag. It never goes in the studio reclaim.
Bring your own
We do not stock stains, oxides or washes. Bring your own jars, and tell the studio team before anything you have brought in goes into a kiln, which is the rule for every outside material. The 150+ underglazes on the wall are stained slips somebody else made, and they are there for the days you would rather buy.
Colouring our clay
Stain wedged into clay from our shelves is still our clay, and it is welcome in the kilns once the studio team knows. Outside clay is not, stained or otherwise. Mix it at the far end of a table with a mask on, over a damp towel, and wipe down wet.
The reclaim
Stained clay never goes into the studio reclaim. A scrap of cobalt clay in the communal bucket is a blue speck in somebody else’s bowl months later. Your own bag, your own name, your own scraps taken home or binned.
Glaze and firing
The glaze wall needs the free brush-on glaze and underglaze certification. A stained slip or wash under one of our clears fires with everything else at cone 5½. Bisque is cone 05 and free; test tiles cost nothing to bisque and pennies to glaze fire, so fire them.
Questions people actually ask
The ones that come up every week.
What is a Mason stain?
A colouring pigment made by firing metal oxides with other minerals into a glass, then grinding it to a fine powder. Because it has already been fired, the colour is stable and predictable: the powder in the jar is roughly the colour the pot will be. Raw oxides are cheaper and wilder; stains are what you use when you want to know what you are getting. Mason is one brand; other suppliers make equivalents and the numbers cross-reference.
How much goes in?
Into a clay body, five to ten percent of the dry clay weight, up to fifteen for weak colours. Into a slip or engobe, five to fifteen percent of the dry weight. Into a glaze, two to ten percent, most colours between two and six. As a wash, roughly equal parts stain and water with a little of the base glaze or a frit added so it sticks. Every one of those is a starting point for a test tile, not a recipe.
Why do some stains die in some glazes?
Chemistry. Chrome-tin pinks and maroons need calcium in the glaze and are killed by zinc. Some blues and greens are fine in almost anything. Encapsulated reds, oranges and yellows fade if fired hot. The jar or the supplier’s chart carries a compatibility note for every colour; read it before choosing a base glaze, and test.
Is stained clay food safe?
A stained clay body under a fitted, fired clear glaze is as safe as the glaze over it. Bare stained clay on a food surface, or a stain wash on a food surface with nothing over it, is not a settled question, and the answer is a coat of clear. Chrome and cobalt stains especially want covering.
Stained slip or bought underglaze?
Underglaze is a stained slip somebody else made, with a binder so it brushes well. Making your own is cheaper per pot, lets you match a colour to your clay, and gives you a hundred colours from one jar and a bucket of slip. Buying it is faster and it brushes better. The Nu Kua video on this page is the honest comparison, and our wall has 150+ underglazes for the days you would rather buy.
Can I colour clay at The Clay Hole?
Stain is bring-your-own; we do not stock it. Colouring a batch of our clay with your own stain is fine so far as the clay is ours, and, as with anything you bring in that will go into a kiln, tell the studio team before it does. Weigh and mix it away from the shared tables with a mask on, and wipe everything down wet.
How do I keep the colour even?
Wet the powder to a paste before it meets clay or slip. Into clay, knead the paste into softened clay and wedge far more than feels necessary, then cut the lump in half and look. Into slip, mix and then sieve through 80 mesh. Into glaze, sieve twice. Uneven stain is almost always dry powder that clumped.
Related lessons
Six lessons that sit next to this one.
Three to read next.
A stain is a colourant; these are the things it colours and the tools that spread it.
That is the whole technique
Pick the use. Read the jar. Mask on. Paste, then sieve or wedge. Tile before pot.
Your first stained clay will be marbled because you stopped wedging when your arms got tired, and your first stained glaze will be paler than the jar. That is normal, and the tiles will tell you which. One jar of a good blue and a bucket of slip is a decade of colours, and the tile drawer is where they live.
If you want the chemistry, the food-safety notes, the dry-weight arithmetic and the answers to the questions everybody asks, switch to the comprehensive version at the top. Otherwise, go read the note on the jar.
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.