How to Use Pottery Overglazes
Real gold, white gold, copper, bronze and mother of pearl go on after the glaze firing and take a third trip through a kiln. They are not hard to use. They are unforgiving about three things, and almost every ruined piece comes from one of those three. Here is the whole process, what to buy, and how to get a piece into our baby kiln.
Overglaze goes on a finished, glazed pot and gets fired a third time, very low. Clean the surface with alcohol, never touch it again with bare fingers, paint one thin coat, fire to cone 018 with the kiln venting. That is the whole job.
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You are painting metal onto glass
Gold luster is real gold, ground fine and suspended in a pine resin oil. You paint that oil onto a finished glazed pot. In the kiln the oil burns away and the metal left behind melts into the surface of the glaze underneath.
So two things decide the result, and neither of them is your brush.
- Whatever is on the glaze when you paint gets fired into the gold. A fingerprint is oil. Oil becomes a dull patch.
- The finish of the glaze underneath becomes the finish of the metal. Gloss gives mirror gold. Satin gives a soft gold. Matte gives a dull one.
Everything else on this page comes out of those two sentences.
The route that works first time
Ten steps. This is gold on a glossy glaze, which is the easiest thing in the family to get right.
- Start with a pot that is already glaze fired and finished. Glossy glaze, no crazing, nothing you are still hoping to fix.
- Wipe the area with rubbing alcohol on a lint free cloth. Let it dry fully. Alcohol carries water and water is a defect.
- From here on, hold the pot with a paper towel. Skin oil is the single most common cause of a dull patch.
- Put on a respirator with organic vapor cartridges. Overglaze is solvent based and the smell is strong. It stays on until the piece is in the kiln.
- Shake nothing. Overglaze does not want to be shaken. Open it and take a small amount onto a clean natural hair brush.
- Paint one thin even coat. It looks brown and unpromising in the bottle and on the pot. That is correct.
- Fix misses while it is still wet. Once it skins over, leave it. A second coat over a dry one goes dull.
- Let it dry an hour, or fire it wet. Both work.
- Fire to cone 018 on a clean shelf, kiln venting, lid cracked early. The fumes are unpleasant and want somewhere to go.
- Let it cool all the way before you open the kiln.
At The Clay Hole that firing happens in our baby kiln, and you arrange it with Dan, the general manager or the studio manager. It is $30 a run.
Three things ruin nearly every piece
You touched it
A fingerprint on the glaze before you paint fires in as a dull grey smudge in the middle of the gold. Wipe with alcohol, then handle the pot through a paper towel until it is in the kiln.
You put it on thick
Thick overglaze fires dull, smoky or brown instead of bright. One thin coat is the whole technique. If the coverage looks weak, that is normal. Resist the second coat.
You fired it too hot
Cone 018 is around 1,300 F, which is a fraction of a glaze firing. Fire gold at glaze temperature and it burns off completely. You get a faintly stained pot and no metal at all.
Read the reasons, watch the hands
Overglaze is one of the few things in pottery where reading gets you most of the way there. The movements are small and slow and there is no timing to learn. What there is instead is a short list of rules that look fussy until you understand what each one is protecting against.
So this page explains the rules and then hands you somebody else's hands. The ten videos are from working potters, none of them us, and each one is placed next to the part of the process it shows.
One honest warning before you spend money. A small bottle of gold luster costs more than a bag of clay, it covers less than you expect, and there is no way to practice cheaply except on test tiles. Read the whole page before you buy anything.
A third firing, and why it has to be cold
Bisque is the first firing. Glaze is the second. Overglaze is a third, and it runs far cooler than either of them, which is the fact that explains everything else.
- What is in the bottle. Metal, ground extremely fine, suspended in an oil made from pine resin. Gold luster is real gold. The bright golds are usually around 8 percent gold by weight, the premium ones around 10, and what ends up on the pot fires out somewhere between 18 and 23 karat.
- What the kiln does. It burns the oil away. That is the smell, and it is the reason the kiln has to vent. What is left is a film of metal sitting on the glaze.
- Why it fires so low. Cone 018 is roughly 1,300 F. Go much above that and the metal film burns off entirely instead of settling. Our glaze firings run to cone 5½, which is more than twice as hot. A luster piece put in a glaze load comes out looking like nothing happened.
- Why the glaze underneath has to be finished. At cone 018 the glaze does not move at all. It will not heal a crack, fill a pinhole, or smooth a rough patch. Whatever you send in, you get back, with metal on it.
- Why the surface finish transfers. The metal is a film a few molecules thick. It takes the shape of what it lands on. Gloss glaze gives mirror bright gold. Satin gives a soft gold. Matte gives a genuinely matte metal, which is beautiful and is not what most people are expecting.
- Why it is always a separate firing. Different overglazes want different temperatures, the fumes want a nearly empty kiln, and the pieces get stilted rather than stacked. It is its own load, every time.
The sentence worth memorizing
An overglaze decorates a finished pot. It does not rescue one. If you are hoping the gold will distract from a problem, it will do the opposite, because a bright metal line draws the eye straight to whatever it is sitting next to.
The family, one by one
They all get painted on a finished pot and fired low, and after that they behave differently enough that mixing them up wastes a firing.
Bright gold and premium gold
The workhorse. Opaque, the color of 22 karat yellow gold, and the easiest of the family to get a good result from. Premium costs more and is worth it: the cheaper golds are more likely to fire with a purple or brown cast. Fires to cone 019 through 018.
White gold and platinum
The same product with a silver finish instead of a yellow one. Handles identically and fires to the same cone. Over a gray glaze it reads as bright as chrome. Over cream it can look slightly warm, which some people want and some do not.
Copper and bronze
Warmer and more variable, and the two most likely to shift color depending on what is under them and how full the kiln is. Treat your first bottle as a test rather than a plan. Excellent on dark glazes, muddy on pale ones.
Mother of pearl
Not a metal at all. A translucent film that throws rainbow iridescence, different at every angle. It goes over a shiny glaze of any color and you want to see the brush strokes, because those swirls are the finished effect. Fires cooler than the golds, to cone 020.
Overglaze enamels, also called china paint
Colored glass rather than metal, painted on and fired low the same way. This is how hand painted porcelain has been decorated for two hundred years. Far more control than underglaze and a far wider color range, and a much longer learning curve.
Decals
The same materials printed on a film. You soak them, slide them on, smooth out every bubble and fire them like anything else here. Cleaner and more repeatable than a brush, and the honest answer for lettering or anything that has to match across a set.
The one combination rule
Golds and mother of pearl on the same pot go on in two separate firings, golds first at cone 018, then the mother of pearl at cone 020. Layering mother of pearl directly over a metallic luster does not work. And keep mother of pearl off copper glazes, where it tends to go cloudy.
Buying it, since we do not stock it
Overglaze is bring your own. We do not carry it and we are not planning to, so the shopping is yours to do. Here is what a first order should contain and what it will roughly cost you.
- One 2 gram bottle of premium bright gold. Two grams sounds like nothing and it is not nothing, but it is not much either. Expect to decorate a small set rather than a dinner service. Buy premium rather than standard for a first bottle, because the standard golds fail in ways that are hard to tell apart from your own mistakes.
- A bottle of essence. This is the thinner. It re-wets overglaze that has thickened in the bottle or dried in a brush, and you will want it by the second session.
- One good natural hair brush, small, and kept only for this. Synthetic bristles do not hold the resin well. A dedicated brush also means you never carry a trace of one overglaze into another.
- Rubbing alcohol and lint free cloths. Cheap, and they do more for your results than anything else on this list.
- Test tiles. Glaze fire a handful of tiles in the glazes you actually use, in gloss, satin and matte. One cheap firing tells you more about how gold will look on your work than any amount of reading.
Do not clean the gold out of your brush
Washing a luster brush in essence and pouring it away throws money down the sink. Wrap the loaded brush in foil instead. A few drops of essence brings it back the next time you use it.
Preparing the surface
More ruined luster pieces come from this section than from every other section put together, and none of it is difficult. It is just easy to skip.
- Pick the right pot. Glaze fired, fully vitrified, no crazing. Crazed glaze pulls overglaze down into the cracks and fires as a dirty web instead of a clean line.
- Decide the finish first. Look at the glaze and decide whether you want mirror, soft or matte metal, because the glaze has already decided for you. If you want mirror gold, the pot needs a gloss glaze.
- Wipe it with rubbing alcohol on a lint free cloth. This takes off kiln dust, the film that fired glaze carries, and every fingerprint from the day it came out.
- Wait. Rubbing alcohol is mostly alcohol and partly water. The alcohol flashes off fast and the water takes longer. Painting onto a surface that still holds moisture gives cloudy metal.
- Stop touching it. From the wipe until it is in the kiln, the pot gets handled through a paper towel. Hand lotion is worse than plain skin oil.
- Check your hands too. Wash, dry, then wipe with alcohol on a paper towel. Everything your brush hand touches ends up in the finish somewhere.
- Work somewhere clean and ventilated. Dust settling on wet overglaze fires in as specks. Moisture in the air is a problem too, which is why breathing directly over the work is a bad habit.
- Put the respirator on before you open the bottle. Overglaze is solvent based and the smell is strong enough to notice across a room. A fitted half face respirator with organic vapor cartridges is the right gear, and it stays on for the painting, for the touch ups, and for loading the kiln. Good ventilation on its own is not the same thing.
Putting it on
It looks like brown varnish going on and nothing about it looks like gold until it comes out of the kiln. Trust the process and keep the coat thin.
- One thin even coat. This is the entire technique and it is the rule people break. Thick overglaze fires dull, smoky, cloudy or brown. If the coat looks too thin to work, it is probably right.
- Fix misses while it is wet. You have a working window of several minutes. Inside it, touch up freely. Once the surface has skinned, stop, fire it, and add more on a second firing if you want it.
- Mother of pearl goes on in swirls. Every brush stroke survives the firing as part of the iridescence, so keep the strokes deliberate and generally running the same way. One thin coat again.
- Solid coverage has a trick. Gold over a yellow glaze or yellow underglaze covers more evenly. White gold does the same over gray. The color underneath stops a slightly thin patch reading as a gap.
- Mistakes lift with alcohol while wet. Wipe it back to clean glaze, let the surface dry properly and start that area again.
- Drying is optional. Overglaze skins in about an hour and pieces can go into the kiln wet. If you have the patience, dry them. If you do not, it will still be fine.
What a satin glaze does to gold
This sake set was made here and decorated with premium gold luster. It is the clearest demonstration we own of the rule that the glaze decides the metal.
The glaze under that gold is a dark satin, not a gloss. So the gold came out warm and soft rather than mirror bright, and every brush stroke is still visible in the finished metal. You can see where the brush lifted at the end of a stroke and where it pressed at the start.
On a glossy black glaze the same gold, from the same bottle, would have come out looking like a mirror, and the brush marks would have mostly disappeared into the shine.
Neither one is the correct answer. It is a decision you make at glazing time, one firing earlier than you think you are making it, and a set like this is worth knowing about before you glaze a piece you are planning to letter in gold.
The baby kiln
Our four production kilns run at cone 05 and cone 5½, which is far too hot for any of this. So there is a small kiln for overglaze work, and it runs for approved projects only.
- What it costs. $30 to run an overglaze firing. That is per firing, not per piece, so a full load costs the same as one earring.
- How big it is inside. 9 inches wide, 9 inches deep and 5.5 inches tall. Measure your piece before you plan around it. The height is the limit that catches people out, because 5.5 inches is shorter than most mugs are tall once they are on a stilt.
- What fits comfortably. Jewelry, ornaments, small bowls, a short lidded jar, a set of cups, tiles, test pieces. A dozen small things go in one load, which is where the flat fee starts making sense.
- What does not. Vases, tall tumblers, dinner plates, anything with a handle sticking out past 9 inches. If a piece is destined for gold, the size limit is worth knowing before you throw it, not after.
- How to arrange it. Ask Dan, the general manager or the studio manager. There is no form and no text line for this one, because each project gets looked at before it is approved.
- Why it is approved rather than open. Overglaze fumes, an unfamiliar firing schedule and a kiln small enough that one badly stilted piece can ruin the shelf and everything else in the load. A quick look before it goes in saves all of that.
Firing it
A short, cold, smelly firing. If you are firing at home rather than here, this is the part to get right.
- Clean kiln, clean shelf. Anything on the shelf that can smoke will land on your metal.
- Stilt the pieces rather than resting them on a glazed foot, and do not crowd the load. Fumes need room to leave.
- Vent it properly. Peeps out, lid cracked for the first stretch, and closed only once the smoke and smell have gone. On a vented kiln, run the vent throughout.
- Golds go to cone 019 through 018. Mother of pearl goes to cone 020, which is cooler. Fire them separately if you are using both.
- Keep the respirator on while you load, then stay out of the room while the binder burns off unless the kiln is vented outside. The fumes are not dangerous in a well ventilated space and they are genuinely unpleasant.
- Cool completely. Opening early puts cold air onto a very thin metal film on a pot that is still moving.
What goes wrong, and what caused it
Overglaze fails in a small number of recognizable ways. Find yours here before you blame the bottle.
Dull, smoky or cloudy instead of bright
Almost always too heavy a coat. Also caused by an uneven one, by moisture on the surface when you painted, or by a glaze underneath that does not get along with the product. Thin it and try one coat on a test tile.
A grey or dull patch in the middle of good gold
A fingerprint, or hand lotion, or a drop of sweat. It was on the glaze before you painted and the firing made it permanent. Alcohol, paper towel, and no bare hands.
A purple or brown cast
Common with standard bright gold and much rarer with premium. Also happens where the coat is too thin over a dark glaze. If it keeps happening with a premium bottle, suspect the surface rather than the gold.
Nothing there at all
It was fired too hot. At glaze temperature the metal burns off and leaves a faint stain. There is no rescue for this except to clean the piece up and start again.
The gold sits in a dirty web of lines
The glaze underneath is crazed and the overglaze wicked into the cracks. This is not fixable at cone 018, because the glaze will not move at that temperature. Choose an uncrazed pot next time.
Specks and pinpricks through the metal
Dust landed on the wet surface, or the kiln was dirty, or the load was crowded and something smoked onto it. A clean bench, a clean shelf and a loose load fix all three.
It rubbed off later
Overglaze is a very thin film on top of the glaze rather than part of it. Scouring pads, dishwasher racks and knives will take it off. That is expected behavior, not a defect.
The second coat looks worse than the first
A coat over a dry coat tends to go dull. If you want more depth, fire the first coat, then apply and fire the second. Two firings, not two coats.
What you can claim afterward
Adding metal to a pot changes what you are allowed to say about it, and the change is bigger than most people expect.
- Not microwave safe. Ever. Metal in a microwave arcs. This is the one rule with no exceptions and no judgment call, and it applies to a hairline band as much as a solid panel.
- Hand wash only. The film is thin enough that dishwasher heat, detergent and rack contact will wear it off. It will not hurt anyone, it will just stop being gold.
- Keep it off the wear surfaces. Gold on the outside of a mug lasts. Gold on the inside of a bowl meets a spoon every time it is used.
- No scrubbing. A scouring pad takes overglaze off in one pass.
- Label it. If it leaves your hands, the person receiving it needs to know it is hand wash and not for the microwave. A pot that fails quietly in somebody else's kitchen is the worst version of this.
The honest summary
A lustered pot is decorative first and functional second. Plenty of people use them daily and they hold up when they are washed by hand and kept out of the microwave. What you cannot do is describe one as dishwasher safe or microwave safe, because it is neither.
The bench checklist
Two short lists. The left one before you open the bottle, the right one before the kiln lid comes down.
Before you open the bottle
- Pot is glaze fired, finished and not crazed
- Glaze finish is the metal finish I actually want
- Piece fits 9 by 9 by 5.5 inches
- Surface wiped with rubbing alcohol
- Surface fully dry, not just alcohol dry
- Hands washed, dried, wiped, no lotion
- Paper towel ready to hold the pot with
- Clean bench, decent ventilation, no dust
- Respirator on, organic vapor cartridges
- Natural hair brush kept only for this
Before the lid comes down
- One thin coat, not two
- Misses touched up while it was still wet
- Nothing bare-handed since the alcohol wipe
- Pieces stilted, load not crowded
- Shelf and kiln clean
- Golds to cone 018, mother of pearl to cone 020
- Peeps out and lid cracked for the burn off
- Brush wrapped in foil, not washed away
The ones that come up at the tables
Can I put a gold piece in a normal glaze firing?
No, and it will not half work. Our glaze kilns run to cone 5½, which is more than twice the temperature gold survives. The metal burns off completely and you get a faint stain where the pattern used to be. Overglaze is always its own firing.
Do you sell luster at the studio?
No. Overglaze is bring your own. We do not stock it, so plan on ordering before you start. The buying section further up this page is what a sensible first order looks like.
How much does a firing cost here?
$30 to run the baby kiln, per firing rather than per piece. Ask Dan, the general manager or the studio manager to set it up. It takes approved projects only, and it is small: 9 by 9 inches and 5.5 inches tall.
Is a mug with a gold rim safe to drink from?
Fired overglaze from a reputable manufacturer is lead free and is not a health problem in normal use. The real answer is about durability rather than safety: hand wash it, never microwave it, and expect a rim you drink from every day to wear before one on the outside of the pot does.
Can I use gold leaf instead?
You can, and it is a completely different thing. Leaf is glued on and never fired, so it sits on top of the glaze and can be scratched off with a fingernail. Luster is fired into the surface and is permanent. Leaf is cheaper and easier. Luster is the one that lasts.
Why does my gold look matte rather than shiny?
Because the glaze under it is matte or satin. The metal takes the surface it lands on. If you want mirror bright gold, the pot needs a gloss glaze, and that decision gets made a firing earlier than most people realize.
How long does a 2 gram bottle last?
Longer than it looks, because the coat is so thin, and not as long as you would like. Think a small set of cups with a design on each rather than a whole dinner service. Wrapping the loaded brush in foil instead of washing it out makes a real difference to how far a bottle goes.
Can I fix a bad gold firing by going over it again?
Sometimes. A thin or patchy area often improves with a second thin coat and a second firing. Dull, smoky or burned off gold does not come back, because the problem is underneath the metal rather than in it.
Where to go next
Food safe, dishwasher safe, what you can claim
The four claims and what each one actually promises. Lusters change all four answers, so read this before you sell a gold pot.
Read it →Glaze problems, causes and fixes
Crazing, pinholes and the rest. Overglaze cannot hide any of them, so the pot underneath has to be right first.
Read it →Underglaze techniques, rules and firing
The other end of the pot. Color that goes on before the glaze and survives a full firing, which is where most decoration belongs.
Read it →What a kiln firing actually does
Why cone 018 and cone 5½ are different worlds, and what is happening to the clay and glaze at each of them.
Read it →Making and logging glaze test tiles
The cheapest way to find out what gold does over your glazes before you commit a finished pot to it.
Read it →Clay Hole University
Every lesson in one place, from first day at the wheel through firing and glaze chemistry.
Start there →Cheap to learn, expensive to guess at
Nothing on this page is difficult. Wipe it, do not touch it, one thin coat, fire it cold. A careful beginner gets a good result on a first attempt more often than not, which is unusual for anything in pottery.
What overglaze punishes is guessing, because the material costs real money and every mistake costs a whole firing rather than a pot. So put the first bottle on test tiles, in the glazes you already use, and find out what your own work looks like with metal on it. Then spend the rest of it on something you care about.
Wipe it with alcohol, stop touching it, one thin coat, fire to cone 018 with the kiln venting. That is the job, and a careful first attempt usually works.
If you want the full family, the shopping list, the firing detail and the eight ways it goes wrong, switch to the Comprehensive Version at the top of the page.
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