Burnishing and terra sigillata: shine without a drop of glaze.
Rub a leather hard pot with a smooth stone and it comes up glossy. No chemistry, no melting, nothing added. You are just pushing the clay flat against itself. Terra sigillata is the same idea with a head start: paint on a layer of the finest particles you can separate out of a bucket of slip, polish that instead, and get a deeper shine for a fraction of the effort. Here is how both of them work, when to do each one, and the part nobody warns you about, which is what our kilns do to that shine afterward.
Rub a leather hard pot with a smooth stone and it comes up glossy. No glaze, nothing melted, nothing added. Terra sigillata is the same idea with a head start. Here is the short version of both, and the one thing our kilns do to that shine that you need to know before you start.
- Wheel or hand building
- No glaze involved
- Intermediate
- An evening, plus drying
They are two different things, and they get talked about as one.
Nearly every video you will find covers both in the same breath, because most potters use them together. They are not the same technique and they do not fail the same way, so it is worth ten seconds to separate them.
Burnishing
You polish the pot itself. A hard smooth tool, usually a stone, gets rubbed over the surface while the clay is at a very specific dampness. Nothing is added. The shine comes out of the clay body you already threw or built.
Terra sigillata
You paint on a very thin layer of ultra fine clay, then polish that. The layer is made by letting a watery slip settle and taking only the finest particles off the top. Those particles are already flat and tiny, so they shine with a soft cloth instead of an hour of stone work.
| Burnishing | Terra sigillata | |
|---|---|---|
| What you are polishing | The clay body | A coating you painted on |
| When you do it | Hard leather hard, and again near bone dry | Any time from leather hard to bone dry |
| Tool | Smooth stone, spoon back, agate | Soft cloth, plastic bag, chamois |
| Time on a mug | Thirty to ninety minutes | Ten minutes of buffing, plus drying between coats |
| Color | Whatever your clay body is | Whatever clay and stain you mixed, so you can change it |
| Grog tolerance | None. Grog wrecks it | Some. The coating fills a little of it |
| Survives our bisque | Partly, and it dulls | Much better |
If you ever lose track of which one you are doing, one question sorts it: are you polishing the pot, or polishing something you painted onto the pot? That is the whole distinction, and every difference in tools, timing and failure comes out of it.
Why there is a list sitting next to every video on this page. Watching somebody burnish is the fastest way to understand the motion. It is also the fastest way to forget the order. Video runs at somebody else’s pace, your hands are busy, and by the time you have the stone in your hand the thing you needed went by four minutes ago. Reading is slower going in and much stickier coming out, because you set the speed and your eye goes back over the part that did not land. So watch the videos for what the motion looks like, and keep the lists open on your phone while you work.
Watch for the motion, read for the order. Video shows you what a burnishing stroke actually looks like. A list is what you keep open on your phone once your hands are busy, because you set the pace and you can go back a line.
Clay particles are flat plates. Shine is just getting them to lie down.
A clay particle is not a grain of sand. It is a flake, wider than it is thick, like a playing card. On a normal dry pot those flakes sit at every angle, so light hits them and scatters in every direction. That scatter is what matte looks like.
Rub the surface with something hard and smooth and you knock those flakes flat, all facing the same way, packed tight. Now light bounces off them the way it bounces off a still pond, and the pot looks wet. That is the entire trick. There is no glass, nothing melted, nothing chemical. It is a mechanical polish, exactly like buffing a shoe.
Terra sigillata gets to the same place by cheating. If you stir clay into a lot of water and walk away, the heavy coarse particles sink first and the finest flakes stay suspended. Pour off that suspended layer and you have a liquid made of almost nothing but the smallest, flattest particles in the bucket. Brush it on thin and it settles into a coat that is already most of the way flat before you touch it, which is why a soft cloth finishes the job in a few passes.
Terra sigillata cheats to the same place. Stir clay into a lot of water, let it settle, and pour off the top layer. What you poured off is nothing but the smallest, flattest particles in the bucket, so it dries almost flat already and a cloth finishes it.
Two things follow from this, and they explain most of the rest of the page. Anything gritty in the clay is a bump you cannot flatten, so grog and sand are the enemy. And a mechanical polish can be undone by heat, because heat starts moving the particles again. Hold on to that second one.
Burnishing, in six steps.
Use a smooth clay body with no grog. Everything below assumes the surface is already smooth, because a burnish magnifies every ridge instead of removing it.
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Get the surface smooth first
Scrape and rib every throwing line off while the pot is still soft. A stone will polish a ridge, not remove it, and a polished ridge is more obvious than a matte one.
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Wait for hard leather hard
Firm enough that a fingernail leaves a mark but no clay comes off on it. Still faintly cool against the back of your hand. This window is the whole ballgame.
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Work one small patch at a time
Two or three inches square. Light pressure, short overlapping strokes, all going the same direction. Finish the patch, then overlap into the next one.
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Keep it barely damp
If the stone starts to drag or squeak, wipe the patch with a barely damp sponge and wait a few seconds. Wet enough to smear is too wet.
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Rims and handles last
They are the thinnest, they dry first, and they chip. Do the belly of the pot while the rim is still catching up.
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Second pass near bone dry
Let it dry slowly overnight under loose plastic, then go over it again with a trace of oil on a cloth. This pass is where the real depth comes from.
Terra sigillata, in five.
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Mix a thin slip and let it settle
Roughly one part dry clay to three parts water by weight, plus a pinch of deflocculant. Blend, then leave it alone for a day.
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Siphon the middle
Three layers form. Pour off the clear water, siphon the fine middle layer into a clean jar, throw out the heavy sludge at the bottom. The middle layer is your terra sigillata.
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Brush it on thin
Onto dust free greenware. Three or four coats that look almost watery. Thick coats flake off.
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Buff as the wet look leaves
Soft cloth, plastic bag or chamois, as each coat goes from shiny wet to just barely matte. Too soon and you drag it, too late and nothing happens.
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Let it dry all the way, then fire
Read the firing section below before you decide where it goes. That part matters more here than it does with glaze.
Two and a half minutes on the only thing that really decides it
Timing is the one variable beginners get wrong, and it is the one that cannot be fixed later. Andy Ward has spent decades on primitive pottery and this is him answering the question directly. Watch it before you pick up a stone.
Mixing and applying, in one sitting
Most terra sigillata videos do the mixing or the applying. This one does both end to end, which makes it the single most useful nine minutes if you are only going to watch one. Sumi von Dassow wrote the book on pit firing and low fire surfaces, so the advice is coming from the alternative firing world where this technique actually lives.
The clay body decides how good this can get.
Burnishing does not remove anything. It flattens what is already there. So every piece of grit, every throwing ridge, every sponge mark gets polished into place instead of polished away, and a shiny defect reads worse than a matte one.
What to look for in a bag
- Smooth and fine. No grog, no sand, no added tooth. Grog particles are harder than the clay around them, so the stone rides over them and leaves a pale scratch on every pass.
- Dark bodies read better. A shine is a reflection, and a reflection shows up against a dark ground far more than against a pale one. This is why so much burnished work is red or near black.
- Porcelain works and is unforgiving. It takes a spectacular polish and it also shows every single stroke boundary you leave behind.
- Our clay bodies are not equal for this. Check the bag, and ask an instructor which of the ones we stock is smoothest before you buy one specifically to burnish.
Getting the surface ready
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Compress and rib while it is still soft
A metal rib on a thrown pot, pulled up the wall in long passes, removes throwing lines properly instead of hiding them. Do this on the wheel, not later with a stone.
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Trim, then rib again
Trimming leaves a slightly torn surface. A flexible rubber rib over the trimmed area at leather hard closes it back up. Our trimming guide covers the cuts themselves.
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Finish with a rib, not a sponge
A sponge pulls the fine particles off and leaves the coarse ones standing proud, which is the exact opposite of what you want. Use a soft rubber rib for the last pass and use the sponge only for moisture.
Do not dry sand greenware to get it smooth. Sanding dry clay puts fine silica dust into the air in a room full of people, and that is the one genuinely hazardous thing in this whole process. If something needs knocking back at bone dry, do it with a barely damp sponge or a green scrub pad held wet, and wipe the surface after. Our studio cleanup rules exist mostly because of dust.
Hard leather hard, and nowhere else.
Everyone who tries burnishing once and gives up got the moisture wrong. Too wet and the stone smears the surface into soft waves that never shine. Too dry and it skates, scratches pale lines, and can flake the surface clean off. The window between those is real, it is narrower than you expect, and you can feel it.
Three ways to test it without guessing
- The cheek test. Hold the pot against your cheek. Cool means water is still evaporating out of it, so it is not there yet. Room temperature means you have gone past.
- The fingernail test. Press a nail into the foot. It should dent, and nothing should stick to your nail. If clay transfers, wait. If it will not dent at all, you are late.
- The color test. Damp clay is noticeably darker than dry clay. Watch the foot ring, which dries last, and start when the walls have gone pale but the foot has not.
Nothing about this window is fixed in hours. A thin porcelain cup in a dry Utah week can pass through it in ninety minutes. A thick hand built jar under plastic can sit in it for two days. Plan around the pot, not the clock, and slow the whole thing down with loose plastic if you need it to wait for you.
The short answer, from somebody who has done it thousands of times
Andy Ward has spent decades recreating the pottery of the American Southwest, which means burnishing is not a decorative option for him, it is the finish. Two and a half minutes, one question, no padding.
Half of a two part demonstration, and the half most people skip
Jason Dunn splits burnishing into two separate sessions at two different dryness levels, which is exactly how good burnished work gets made and exactly what a single tutorial usually leaves out. This is the first pass. The second one is further down this page, and they are worth watching in order.
Burnishing, properly, start to finish.
Plan on thirty to ninety minutes for a mug and considerably more for anything bigger. This is genuinely slow work, and rushing it is visible in the result, which is most of why so few people do it.
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Test on a scrap first
Every stone behaves differently and every clay body reaches the window at a slightly different feel. Burnish a coil or an offcut from the same batch, at the same time, and you will know within thirty seconds whether the pot is ready.
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Start with light pressure
The first pass is about laying the particles down, not forcing them. Heavy pressure on a surface that has not been compacted yet will gouge. Go light, get the whole area evenly dulled and slightly slick, then come back harder.
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Work small patches and overlap them
Two or three inches at a time. If you try to cover a whole side, the far end dries while you are still on the near end and you will see the boundary forever. Finish a patch, then start the next one an inch inside the last.
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Keep the strokes going one direction, then cross them
Consistent direction gets the particles aligned. A second pass at roughly ninety degrees to the first fills in the microscopic tracks the first one left. On a thrown form, go around the pot first, then up and down.
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Manage moisture constantly, in small amounts
If the stone squeaks or grabs, the patch has dried past the window. A barely damp sponge wiped over it and ten seconds of waiting brings it back. Never enough water to see a sheen, because that is wet enough to smear.
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Build pressure on the second and third pass
Once the surface is compacted and slick you can lean on it. This is where the shine actually arrives, and it arrives suddenly rather than gradually, so keep going past the point where it looks merely smooth.
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Rims, handles and feet last
Thin edges dry fastest and chip easiest. Do the body of the pot while those are still catching up, then come back to them with lighter pressure and a smaller tool.
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Dry it slowly on purpose
A burnished surface that dries fast can go dull again as the surface shrinks away from the compacted layer. Loose plastic, a day or two, no fans and no sunny windowsill.
Fourteen minutes of the actual motion, in a modern studio
If the list above tells you the order, this tells you the feel. It is recent, it is unhurried, and you can watch the surface change under the tool in real time, which is the part writing cannot do. Worth having playing on a bench while you work through your first pot.
Anything hard, smooth and seamless.
There is no correct burnishing tool. There is only a surface harder than leather hard clay with no edge, no seam and no chip in it, because every one of those prints itself onto the pot.
A river stone
The traditional answer and still the best one. Look for agate, jasper or any dense stone worn glassy by water. You want a few shapes: one rounded for open curves, one with a pointed end for inside a rim, one flat for broad walls.
The back of a metal spoon
Free, in every kitchen, and genuinely good. The bowl of the spoon fits a convex wall well. Check for a manufacturing seam along the edge first, because it will score a line all the way around your pot.
A polished glass bead or marble
Excellent for tight curves and inside small openings. Glass is hard, perfectly smooth and does not hold water the way a porous stone can.
A plastic bag over a fingertip
Not for the main burnish, but very good for softening stroke boundaries at the end and for polishing terra sigillata. Your finger follows the form in a way a rigid tool cannot.
Chamois or a soft cloth
The standard finish for terra sigillata and a good final buff on a burnish. Old cotton t-shirt works as well as anything you can buy.
Bone, antler or hardwood
What most of the world used for most of history. Softer than stone, so it is gentler and slower, and it will not chip a delicate rim the way a stone can.
What not to use
- Anything with a manufacturing seam. Spoons, plastic tools and cheap ribs often have one, and you will not see it until it is on the pot.
- A chipped stone. One chip becomes one scratch, repeated across the entire surface.
- Metal ribs used on edge. The edge is the point of a rib, which makes it the wrong shape for this.
- Anything porous and unsealed. It picks up clay, dries, and turns into sandpaper mid-pass.
Proof that you do not need to buy anything
Two minutes, one spoon, a visible result. We include it because the most common reason people never try burnishing is thinking they need a special stone first, and they do not. Try it with a spoon tonight and buy a stone later if you like the technique.
Come back at bone dry with a trace of oil.
One burnish at hard leather hard gives you a nice satin surface. The deep, wet looking shine that makes people pick a pot up comes from a second pass, days later, on a surface that has already been compacted once.
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Let it get all the way to bone dry
Slowly, under loose plastic for the first day. The surface will go noticeably duller than it was when you finished. That is normal and it is not lost.
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Put a trace of oil on a soft cloth, not on the pot
A drop of vegetable oil, mineral oil or a solid vegetable shortening, worked into the cloth until the cloth barely looks damp. Applying oil directly makes a slick that will not burnish and can leave a stain.
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Wipe a small area, then burnish it dry
The oil is a lubricant so the stone can slide on a dry surface without scratching. Work the area until the oil is gone and the surface is glossy, then move on. Any oil left sitting on the surface is too much.
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Finish with a dry cloth
A last buff with clean cotton evens everything out and picks up any oil you missed.
Go easy on the oil. Enough of it will burn out in the firing and carbonize, leaving grey smudges you did not plan, and on a pot headed for a smoke firing it can make the pattern muddy rather than dramatic. A cloth that looks dry and feels faintly slick is the right amount.
The second half of the pair from earlier on this page
Same pot, days later, dry. Watching the two videos back to back is the clearest demonstration anywhere of why this is two sessions and not one, and how much of the final shine is sitting in the second one.
The finest clay in the bucket, and nothing else.
Terra sigillata is not a glaze, not a slip in the ordinary sense, and not a product you have to buy. It is a separation. You take ordinary clay, suspend it in a lot of water, and let gravity sort it by particle size. The coarse fraction sinks. What stays floating is a liquid made of the smallest, flattest particles the clay contains, and that is the material.
Because those particles are already tiny and plate shaped, they pack down almost flat on their own as the coat dries. A soft cloth finishes the alignment in a couple of passes. You are getting most of the result of an hour with a stone for about ten minutes of buffing, which is why so many potters working in pit and smoke firing use it as their default surface.
The name comes from Roman pottery, where it referred to the stamped decoration rather than the surface, so the modern usage is a bit of a misnomer that has been in place long enough that arguing about it is pointless. What matters for you is that it is cheap, it is made from materials that are already in a pottery studio, and it will keep in a jar for years.
Reasons to use it
- Far less labor than burnishing for a comparable or better shine.
- You choose the color, independent of the clay body underneath.
- It fills small imperfections instead of magnifying them.
- It holds its sheen through a hotter firing than bare burnishing does.
- It takes smoke, carbon and horsehair beautifully.
Reasons not to
- It is a coating, so it can flake off if applied wrong. A burnish never can.
- Making a batch takes a day of waiting, mostly unattended, but a day.
- It hides the clay body, which is the whole point for some people and a loss for others.
- Getting a color you like takes test tiles, the same as glaze does.
Water, clay, a pinch of deflocculant, and a day of patience.
Recipes vary widely and most of them work. The ratios below are a reliable starting point rather than a sacred formula, and the number that actually matters is the thickness at the end, not the amounts at the start.
| Ingredient | Proportion by weight | What it does |
|---|---|---|
| Water | 3 parts | Enough volume for the particles to separate by size as they settle |
| Dry powdered clay | 1 part | The material. Ball clay, Redart or a kaolin, depending on the color you want |
| Deflocculant | About half a percent of the dry clay weight | Breaks up clumps so individual particles can settle on their own. Sodium silicate, soda ash or sodium hexametaphosphate |
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Dissolve the deflocculant in the water first
Not into the clay. A tiny amount goes a long way, and undissolved lumps will not do their job. Too much and nothing settles at all, which is a slow way to find out you have gone wrong.
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Add the clay and blend it hard
A drill mixer or a blender kept for studio use. Five minutes of real agitation. Every clump left intact is fine material that will end up in the discard layer instead of your jar.
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Leave it completely alone for twelve to twenty four hours
In a tall clear container so you can see the layers. Do not bump it, do not check it by stirring. Longer settling gives you a finer, glossier, smaller yield. Shorter gives you more of a coarser product.
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Read the three layers
Clear or slightly cloudy water on top. A cloudy, colored middle layer. A dense sludge at the bottom. The middle is what you want.
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Siphon the middle into a clean jar
Pour or siphon off the clear water first, then siphon the middle layer with a length of tubing. Stop before you disturb the sludge. Throw the sludge in the reclaim bucket rather than the sink.
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Check the thickness and adjust
Weigh 100 millilitres of it. Around 110 to 120 grams is right. Thinner than that, let it evaporate with the lid off. Thicker, add water. Thin is safer than thick, always.
Picking a clay for color
A ball clay such as OM-4 gives a creamy off white and is the usual default. Redart gives a warm terracotta through to a deep red and takes the highest shine of the common options. Kaolins give the whitest result with somewhat less gloss, because the particles are a little coarser and blockier.
Adding color
Mason stains at roughly two to five percent of the dry clay weight, or oxides at one to three percent, added after siphoning. Make test tiles and fire them the way the real pot will be fired, because these colors shift dramatically between a smoke firing and an oxidation bisque.
You can also make it out of what is already here. The fine slop in a reclaim bucket is most of the way to terra sigillata already. Thin it heavily with water, let it settle, and siphon. The result is unpredictable batch to batch, so it is not what you want for a set of matching pots, but it costs nothing and it is an excellent way to find out whether you like the technique. If you are working with clay you dug yourself, our wild clay page covers the settling and screening side of it in more depth.
The demystifying one, if the recipes have you nervous
Terra sigillata gets written about as though it needs laboratory precision, and it does not. This is the antidote to that, from somebody who makes it out of ground he walked to. Watch this first, then the recipe video below if you want measured numbers.
The measured, scaled down version
A lot of published recipes make gallons of the stuff because it is a nuisance to make. This one is scaled to a batch a single person can actually use up, with the weighing and the settling shown clearly. Good companion to the list above.
Thin coats, and buff in a short window.
Almost every terra sigillata failure is one of two mistakes: the coat was too thick, or the buffing happened at the wrong moment. Everything below is about avoiding those two.
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Start with clean, dust free greenware
Leather hard or bone dry both work, and bone dry is easier to handle. Wipe the surface with a barely damp sponge and let it re-dry. Dust is the single most common reason a coat lifts off later.
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Brush on a coat that looks too thin
A soft wide brush, quick even strokes, no going back over a wet area. It should look watery and slightly translucent. If it looks like you are painting, it is too thick.
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Change direction with each coat
Horizontal, then vertical, then horizontal. Three to four coats total. Let each one lose its wet look before the next, which is usually a minute or two.
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Buff as the shine leaves the surface
The window is short. Too early and the cloth drags the coat off in streaks. Too late and you are polishing a dry powder that will not move. Watch for the moment it goes from wet looking to just barely matte and go then.
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Use something soft
A plastic grocery bag over your fingers, a chamois, or a piece of old t-shirt. Light pressure, small circles or short strokes. A stone works too and gives an even harder gloss, but it is easy to cut through a thin coat with one.
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Let it dry completely before firing
The coat is thin but it is still water going into a kiln. Treat it like any other greenware and give it the time.
Combining the two techniques
Burnish the bare clay lightly first to compact the surface, then apply terra sigillata over it and buff that. You get the density of a burnish underneath and the fine particle gloss on top. It is more work than either one alone and it is the route to the deepest shine.
Spraying instead of brushing
A spray gun or an airbrush lays down thinner, more even coats than a brush and avoids stroke marks entirely, which matters on a large or complex form. Wear a respirator and spray in a booth, because an airborne clay mist is a dust problem like any other.
Mixing and application in one go
Sumi von Dassow works almost entirely in pit firing and low fire surfaces, which is exactly the world this technique belongs to. Watch the buffing timing here in particular, because that moment is the hardest thing to describe in words and the easiest thing to recognize once you have seen it.
Terra sigillata problems and what caused them.
It flakes or peels off
Almost always too thick. Sometimes dust on the pot underneath. Occasionally too much deflocculant, which leaves the coat brittle. Thin the batch with water and use more coats.
No shine at all
Either the coat is too thick to polish, or you buffed after it was already dry, or the batch did not settle long enough and is still carrying coarse particles. Let the next batch settle a full day.
It streaks when you buff
You went in too early, while the coat was still wet enough to move. Wait for the surface sheen to go and try again on the next coat.
Visible brush marks
Coat too thick, brush too stiff, or you went back over a half dry stroke. Load the brush more, move faster, and do not touch an area twice in the same coat.
It crawls or beads up
Something on the surface is repelling it. Wax, oil from your hands, or a fingerprint from handling the dry pot. Wipe with a damp sponge, let it dry, and recoat.
The jar has separated
Normal, and not a problem. Stir it gently rather than shaking, so you do not whip air into it, and check the thickness again if it has been sitting for months.
Twelve minutes aimed squarely at what goes wrong
Most tutorials show you a batch that worked. This one spends its time on the batches that did not, which is far more useful the second time you make it. Jeremy Randall builds his work around terra sigillata surfaces, so the troubleshooting comes from repetition rather than theory.
Heat undoes a polish. Our kilns are hot.
This is the part that catches people, and it is worth knowing before you spend an hour with a stone rather than after.
A burnish is a physical polish. As firing temperature climbs, the particles you flattened begin to move and sinter, and the shine softens. Potters chasing the maximum possible gloss from burnishing alone often fire as low as cone 018. We bisque to cone 05, about 1,888°F, which is a good deal hotter than that, so a purely burnished surface comes back from our bisque less glossy than it looked when you put it on the shelf.
Terra sigillata holds its sheen far better through a cone 05 bisque than bare burnishing does. If you want that hard polished look coming out of our kilns, terra sigillata is the route, and it is the main practical reason to pick it over the stone.
A glaze firing is a different conversation entirely. Ours goes to cone 5½, just over 2,180°F, and nothing about a polished surface survives that. Whatever sheen you had is gone, and the pot comes out looking like ordinary matte stoneware. There is no version of this technique that ends in our glaze kiln.
A glaze firing at cone 5½ erases the sheen completely. There is no version of this technique that ends in our glaze kiln.
Do not glaze over it
A glaze needs something to grab, and a burnished surface is deliberately as slick and closed as you can make it. On top of that, glaze covers the polish you just spent an hour creating. If a piece needs glaze, do not burnish it.
It is not waterproof and it is not for food
A burnished or terra sigillata surface fired low is still porous clay. It will absorb liquid, it will stain, and it should be treated as decorative. Water and dishwashers also dull the shine, so keep these pieces dry.
Talk to us about the firing before you commit an evening to polishing. Bisque firing here is free and goes to cone 05, and our alternative firings run on their own schedules and their own calendar. Knowing where a pot is headed changes which of these two techniques you should be using on it. Our page on what a firing actually does covers the underlying chemistry if you want it.
Burnished surfaces exist for the smoke firings.
Every technique on this page was developed in a world without glaze, and it still does its best work in firings that behave like that world. A polished surface is what makes carbon, smoke and horsehair read as sharp marks instead of a grey smudge, because there is nothing porous for them to sink into.
Two minutes showing why any of this is worth the trouble
Marcia Selsor takes a terra sigillata surface straight through to a horsehair and feather firing, so you see the whole arc from polished pot to finished piece. If you have been wondering what the payoff looks like, this is it, compressed.
Eight things that go wrong, and what each one means.
The three you will actually hit.
Pale scratchy lines
The surface was too dry when the tool went over it, or there is grit in the clay or on the stone. Wipe the patch with a barely damp sponge, wait a few seconds, and check your tool for a chip.
A soft, smeared, wavy surface
Too wet. You are pushing the clay around instead of compressing it, and no amount of extra polishing will fix it at this dampness. Stop, let it firm up, come back.
It came out of the bisque dull
Temperature, not technique. A cone 05 bisque takes the edge off a bare burnish. Use terra sigillata for a surface that survives our kilns, or send the piece to one of the cooler alternative firings instead.
Visible bands of different shine
You burnished patches at different moisture levels, so each one compacted differently. Work in smaller sections, overlap them, and keep the whole area at one dampness rather than letting the far side dry.
The shine faded while it dried
It dried too fast and the surface shrank away from the compacted layer. Loose plastic for the first day next time, and recover this one with the oiled bone dry pass.
The rim chipped
You burnished a thin edge that had already gone past the window while the body of the pot was still in it. Rims last, lighter pressure, smaller tool.
Grey or brown smudges after firing
Too much oil on the bone dry pass, carbonizing in the kiln. Work the oil into the cloth rather than onto the pot, and buff every trace of it off before the piece dries.
It looked great and then somebody washed it
Water dulls a low fired polished surface, and a dishwasher destroys it. These are dry, decorative pieces. Dust them, do not wash them.
Two long ones, for when you are not standing at a bench.
Everything above is built to be usable with clay on your hands. These two are the opposite: sit down, take notes, and come out understanding why the rest of it works.
Twenty three minutes on burnishing as a whole subject
Slower and more complete than any of the technique clips above, covering the reasoning behind the choices rather than just the motions. The one to watch if your first pot came out wrong and you want to understand why instead of trying again blind.
A full conference lecture, and the most authoritative hour on the subject
Peter Pinnell and Rhonda Willers presenting at NCECA, the national ceramics conference. This is where a lot of the recipe advice circulating online originally came from, delivered by the people it came from, with the reasoning intact. An hour, and worth it if terra sigillata becomes your thing.
The rest of it.
Can I burnish a pot I already bisque fired?
No. Burnishing works because damp clay particles can still be moved. Once a pot has been fired the particles are locked, and rubbing it with a stone does nothing at all. This has to happen on greenware.
Can terra sigillata go on bisqueware?
It can, and it is done, but it bonds noticeably worse than it does on greenware and is more likely to flake. If you have the choice, apply it before the bisque. If you are salvaging a piece you already fired, expect to use extra thin coats and to accept a less reliable result.
Do I have to use a deflocculant?
No, and plenty of people skip it. Without one the separation is slower and less complete, so you get a smaller yield of slightly coarser material. With one you get more of a finer product in less time. Try it both ways with the same clay and see whether the difference matters to you.
How long does a batch keep?
Years, in a sealed jar. It will separate, which is normal, and it may develop a smell, which is also normal and harmless. Stir gently, check the thickness, and use it.
Can I put underglaze under or over terra sigillata?
Underglaze under terra sigillata generally works and the polished coat over the top gives it a soft sheen. Over the top is less reliable, because you are putting a matte layer on the thing whose whole purpose is to be glossy. Our underglaze page covers the firing rules for those, which still apply here.
What is the difference between terra sigillata and an engobe?
Particle size and purpose. An engobe is a formulated slip designed to fit a clay body and carry color at stoneware temperatures, applied relatively thick. Terra sigillata is an unformulated fine fraction applied extremely thin, for shine rather than for coverage. Our engobes page has the full comparison.
Is this beginner friendly?
The motions are simple and anybody can do them on their first day. What makes it intermediate is judgment: reading moisture, knowing when to stop, and choosing a firing that matches the surface. Expect the first pot to teach you something the second one gets right.
Can I burnish something made on a slab roller or in a slab mold?
Yes, and the flat panels are easier to work than a curved thrown wall. Watch the canvas texture, which a slab roller leaves behind and a burnish will happily polish into permanence. Rib it out while the slab is still soft, before you build anything.
Related lessons.
Try it on something you do not care about.
Go find a spoon.
This is one of the few techniques in pottery where the whole thing can be learned in a single evening on a test tile. Roll out a slab, cut it in four, and burnish each piece at a different dryness. You will know more about the moisture window from that one hour than from any amount of reading, including all of this.
Then pick the technique that matches where the pot is going. Bare burnish for the cooler alternative firings, terra sigillata for anything coming out of our own kilns, and neither one for a piece that needs glaze. Get that decision right and the rest is just patience and a smooth stone.
Roll out a slab, cut it in four, and burnish each piece at a different dryness. One hour will teach you the moisture window better than this page can. Then pick terra sigillata if the pot is coming out of our own kilns, and a bare burnish if it is headed for a pit or a smoke firing.
There is a considerably longer version of this page with both techniques in full, every tool, all twelve videos and the whole troubleshooting list. The toggle is at the top.
Which version would you like to print?
Videos come out as a labelled box with the title and channel to search for, since paper does not play them.