Step by step · Slab molds

How to get a beautiful piece off a slab mold, every single time.

This is the walk-along version. Open it at your table, work down the steps in order, and tick things off as you go. It follows our slab mold video closely, in the order you will actually do it.

A serving bowl that takes years of practice to throw on the wheel, you can make properly on a slab mold on your first night. These twelve steps are the difference between doing that and doing it well. Your ticks save on this device, so you can close the page mid-piece and pick it back up.

Twelve steps, stripped to what you do and what goes wrong. Work down them in order and tick as you go. Your ticks save on this device, and they carry across if you switch to the long version.

Not certified on the slab rollers and slab molds yet? That part comes first, and it is required before you use either.Get certified
An illustrated potter lifting a large clay slab and draping it over a white dome slab mold set on a banding wheel, with hand tools and a rolling pin on the table beside her

Every step with the reasons behind it, the repairs, and the whole tool list.

The short of it

Bigger, thicker, slower, drier.

Four ideas carry the whole page. Every step below is one of them, in the order you will actually do it.

Bigger

Measure the widest point of the slab mold and roll a slab an inch wider than that. There is no adding clay back once it is draped.

Thicker

A third of an inch up to thirteen inches across, half an inch above that. Thin slabs warp in the kiln and leave you nothing to paddle into.

Slower

Lay the slab down, never drop it. Press with palms, never fingertips. Clay remembers being rushed, and it gives all of that back while the piece dries.

Drier

Finish the surface with a rib and as little water as you can. And nothing wet or sharp ever touches the slab mold itself.

Part one · Before you touch clay

Both of these happen in the slab mold room and at your table, before any clay gets cut.

Step 1. Pick your slab mold

In the slab mold room, before you touch any clay.

Your own membership color and everything below it, never above. Round and oval shapes drape with almost no effort. Sharp corners fold, and a fold has to be cut out and rejoined.

Every slab mold in the room has a colored sticker underneath it. That sticker is the whole system. You get your own membership color plus every color below it, and never a color above it.

  • Green Level uses green
  • Yellow Level uses green and yellow
  • Purple Level uses all three
  • Black Level uses everything

Bigger and more expensive sits higher up the ladder, and almost the whole room is open to you by Purple Level.

Shelves of white plaster slab molds in The Clay Hole mold room, each one carrying a colored membership sticker, with domes and troughs stacked from floor to ceiling
The slab mold room. Look along the shelf edges and you can see the stickers: purple, yellow, green.

Take one out at a time

One slab mold, until you have a few pieces behind you. Once you know the rhythm you can run two or three at once. Dip your toes in first, then expand.

Look at where it lives before you lift it

That exact spot on that exact shelf is where it goes back at the end of the night. If you already know you will not remember, take a photo of the shelf before you pick it up. Nobody will judge you for it. Half of us do it.

Where it goes wrong

Sharp corners are the hard ones. Clay will not drape around a corner, so you get folds that have to be cut out and mended back together. That is a different evening than the one most people signed up for. Every other shape in the room is built to have a slab laid straight over it and will look beautiful with very little effort.

If you want a sharp-cornered one anyway, step 8 has the full fold repair.

Plaster and wood

Most of our slab molds are plaster and there are more wooden ones every month. Plaster and fiberboard molds pull water out of the slab, so the piece lets go on its own, and every rule on this page applies to them. Ceramic, metal, stone and sealed wood molds do not, so those get wrapped in plastic before the clay goes on, or the piece sticks and tears coming off.

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Step 2. Set up your station

At the pottery tables, with your slab mold in front of you.

The trade-off: the needle tool cuts nicer, and it can also shave plaster into your clay, which is what splits somebody’s bowl weeks after it came out of the kiln. The wooden knife cannot. Keep water within reach and then try not to use it.

Every slab mold sits on a banding wheel. You want the wheel to sit under it without digging into it, and most of ours are perfectly happy on the small banding wheels.

A flat-bottomed slab mold goes straight onto the wheel. If yours has a concave bottom, and some of the bigger ones do, drape a dry clean rag over the wheel first and set it down gently on top of that.

What you need on the table

A wire cutter

For cutting clay off the block.

A soft red rib

These bend as you work, and they are what makes a surface pristine. Green Level Members bring their own tools. Every other Level uses the studio ribs.

A pottery sponge

The yellow ones are great for this kind of work.

A wooden potter’s knife or a needle tool

Pick one. See below, because it matters more than it sounds like it does.

Knife or needle tool

The needle tool cuts noticeably nicer and easier. It can also shave plaster off your slab mold if you get careless with it, and plaster in your clay is what splits somebody’s bowl down the middle weeks after it came out of the kiln. The wooden knife cannot do that, and it is almost as good.

It is a real preference either way, as long as you know which risk you picked up.

Fill a small bucket of water and put it within reach. Then try to finish the whole piece without touching it. That is not a joke, it is the goal, and step 10 explains why.

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Part two · Getting the slab right

Almost every disappointing piece was decided in these three steps, long before it looked wrong.

Step 3. Do the math before you cut anything

Two numbers, worked out here instead of discovered later.

A third of an inch up to thirteen inches across, half an inch above that. Never go thinner to save clay: thin warps in the kiln and leaves you nothing to paddle or stamp into.

Almost every ruined evening on a slab mold starts with a slab that was too small or too thin. Both are decided right now, before any clay gets cut.

How wide the slab has to be

Measure the widest point across your slab mold and add at least half an inch. A full inch is better. So a slab mold that is thirteen and a half inches across wants a slab that is fourteen to fourteen and a half inches at its narrowest point.

Work that out now, not after you have rolled a slab and carried it across the studio.

How thick

A third of an inch for a slab mold around thirteen inches across or smaller. Half an inch for anything bigger than that. Those are wet-clay numbers, and they leave you enough clay to paddle, texture stamp or add embellishments without going through the wall.

Never go thinner to save clay

The thinner the slab, the more the piece wants to warp in the kiln. Clay is the cheapest part of this evening and most of the trimmings go straight back into your bag anyway.

Work it out here

inches

Roll a slab

14.5 inches across

at its narrowest point

Thickness

Half an inch

wet clay, before it dries

Cut roughly

About 8 lb of clay

about a third of a 25 lb bag

Rough numbers, and rough is fine. Cut a little extra, because most of the trimmings get wedged up and go straight back in your bag.

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Step 4. Cut the clay and get the block under three inches

At the clay table, with your wire cutter.

Fresh from the bag it needs no wedging, because it left the pug mill wedged and the roller compresses it again. Under three inches or the bar cannot come down on it. Slam it flat at an angle, rotate, slam again.

Close enough is usually good enough here. Cut a rough block off the bag with the wire cutter and weigh it if you want to. Most of what you cut off comes back to you anyway, because the trimmings get wedged up and go straight back in the bag for the next piece.

Do you need to wedge it?

If it is coming straight out of a fresh bag, no. Fresh clay leaves the pug mill already wedged, and it is going through the slab roller next, which compresses it all over again. If you want it softer and more workable in your hands, wedge it. There is no wrong answer here.

Under three inches

This part is not optional. The block has to be under three inches tall before it goes on the slab roller, or the bar cannot come down on it. Slam it flat on the table at an angle, rotate it, slam it again. It stretches out sideways and gets shorter every time.

Where it goes wrong

People try to save a pass by starting with a block that is nearly four inches tall, then force the roller down onto it. That is how the machine gets hurt. Spend the extra thirty seconds on the table.

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Step 5. Roll the slab

At either slab roller. Both are open to every Level.

The small marks between the big ones are the eighths, and almost everybody reads them all as quarters the first time. Clay only stretches side to side, which is why you rotate it. Found a soft blister? Pierce it once with the tip of a needle tool, press the air in toward the hole, close it with the rib and roll the slab again.

Both of our slab rollers are open to every Level and both will roll a slab up to thirty inches. This is fiddly the first time and quick by the third, so give the first one some patience.

Setting up

Your clay goes between the two mats, centered. Crank the roller bar up to about three inches to start, since that is roughly the height of your block, then lower it a little with every pass.

Read the gauge in eighths, not quarters

This is the single most common mistake on the machine. The big marks in the middle are quarter inches. The smaller marks next to them are eighths. Almost everybody reads them all as quarters the first time and lands nowhere near the thickness they wanted.

The other half of that: the lower the bar goes, the more each increment does. A quarter inch change at the start barely touches the clay. A quarter inch change when the slab is already half an inch thick would double its length.

Each pass

Grab both ends of the mat and pull until you feel tension against the roller bar. That is how you know the clay has reached it. Pull ever so slightly, then start turning the wheel slowly until the whole thing is through and there is no tension left.

If the wheel is really hard to turn, you dropped the bar too far in one go. Raise it back up and take smaller steps. Never force it.

Keeping it square

Clay only stretches from side to side as you look at the machine. It does not stretch front to back. So rotate the slab ninety degrees as you go, and keep it centered on the mats. Square is what you want, because square is the shape you are draping over a round slab mold.

At least once during the process, flip the slab over as well as rotating it. That helps it release cleanly if it has started sticking to one of the mats.

The last pass, and getting it off

Set your real thickness, remembering that the gap includes the thickness of the mats, so you are landing a little under the number on the gauge. Send the final pass through both ways.

Then lift the top mat straight off and peel the bottom one back slowly. Yank the clay instead and the whole mat comes up with it, and a perfect slab is gone in about a second.

You found an air bubble in the slab

You will eventually, especially with clay you wedged yourself or with scraps from other pieces. It shows up as a soft blister that rises again a moment after you press it flat.

It is not going to blow your piece apart in the kiln. What it does is leave a void, and the surface follows that void as the piece dries and shrinks, so you end up with a blister on a bowl you spent a whole evening on.

  1. Find the edges of it with a flat palm. It feels springy compared with the clay around it.
  2. Pierce it once with the very tip of a needle tool, straight into the center at a shallow angle. One hole is all you want.
  3. Press the air out from the outside of the blister in toward the hole, using your fingertips or the flat of a rib, until it stays down.
  4. Compress the hole closed with the rib and smooth over it.
  5. Send the slab through the roller one more time at the same setting, or one notch lower. That re-compresses the whole slab and the repair disappears.

If a slab has three or four of them in it, do not fix them one at a time. Wedge the whole thing up and roll a fresh slab. It is faster, and you were going to reuse that clay anyway.

Any hand-building instructor will show you this in about ninety seconds if you would rather watch it once than read it.

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Part three · Onto the slab mold

Slow hands from here. This is the stretch where a slab becomes a piece.

Step 6. Trim it round and carry it over

Still at the slab roller, then back to your table.

Squeeze it and the fingerprints press all the way through the piece, and those take real work to smooth back out.

One side of a rolled slab is almost always longer than the other. Come in with your needle tool and shave the extra off until it is closer to a circle. It will drape over the slab mold far more easily and you will have less to cut away later. Wedge those scraps up and put them back in your bag.

Clay has a memory

This is the part people underestimate. Clay remembers being flopped around and manhandled, and it gives all of that back while the piece dries, not in the kiln. Keep the slab as flat as you can and move slowly. Every bit of this step is slower than it feels like it needs to be.

Picking it up

Hold it between your fingers and your palm and lift it off the mat that way. Squeeze it and you get fingerprints pressed all the way through the piece, and those take real work to smooth back out.

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Step 7. Drape it

One slow movement. This is the moment the piece is decided.

Drop it from height and whatever hits first stretches thin, which you will not see until the kiln. Uneven overhang means you run out of clay on one side in step 9, and there is no getting it back.

Hold the slab above the slab mold and hang it down until you can see the bottom edge of the slab sitting below the edge of the slab mold. Then very slowly lay it across.

If it lands off center, lift it and shift it. Do not drag it. You want the flaps and frills of clay to be reasonably even all the way around, because uneven now means you run out of clay on one side in step 9 and there is no getting it back.

Where it goes wrong

Dropping it from height. The slab lands, spreads unevenly, and stretches thin in whatever spot hit first. You will not see it now. You will see it in the kiln.

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Step 8. Cut the big flaps off

Rough cuts only. The finished edge comes later.

Going straight sideways is what makes this forgiving: you cannot take off too much that way. Specks of plaster crack your own piece, and the groove you leave behind gets copied by every piece made on that slab mold afterward. Sharp-cornered slab mold? The fold repair is in the Comprehensive Version.

First, find where the final cut is going to be. Take your needle tool and run it straight up against the slab mold until you feel it stop at the bottom edge of the form. That is your line. Not yet, though.

Right now you are only getting rid of weight. All that hanging clay is dragging the slab down and away from the form, and you cannot press the piece on properly while it is there.

Cut straight sideways. That is the whole trick.

Go straight sideways. Then adjust, so the cut part comes away and the next part of the flap drops down. Then cut straight sideways again. Keep going all the way around.

What beginners do is start following where they think the curve is going, and they cut too much. If you always go straight sideways, you can never take off too much. It is a very forgiving move and it looks wrong until you have done it once.

Never cut down into a slab mold

Straight across, never down into the plaster. This is the exact moment the sharp tool rule usually gets broken. A few specks of plaster in your clay is what cracks your own piece weeks after it comes out of the kiln, and the groove you leave behind gets copied by every piece made on that slab mold afterward.

You are not trying for a clean finished edge here. You are just taking the weight off. The neat cut happens in step 9.

Your slab mold has sharp corners

Clay will not drape around a corner. It bunches up into a fold, and a fold left in place is a crack waiting to happen. So you cut it out and put the clay back together properly.

The fold stands proud of the slab mold at the corner, which means all of this cutting happens in the air above the form. Nothing here goes down against the plaster.

  1. Press the slab down onto the flat faces first and let the fold stand up on its own at the corner. Do not flatten it.
  2. Cut down through both layers of the fold in one straight pass with your needle tool, following the line of the corner. You now have two clean edges that meet.
  3. Take the wedge of waste clay out.
  4. Score both edges. Scratch a crosshatch right across the face of each edge with the needle tool, so both mating surfaces are roughed up.
  5. Wet the score marks with a little slip, which is just clay and water mixed to about the thickness of yogurt. A fingertip is plenty. A dry seam is a seam that opens in the kiln.
  6. Press the two edges together and hold them. Then compress the joint from both sides with your wooden knife or a rib, working the clay across the seam until you cannot see where it was.
  7. Roll a thin coil of the same clay, lay it along the inside of the seam and blend it in with the rib. That coil is what makes the joint as strong as the rest of the wall.
  8. Smooth the outside with the red rib, slowly, keeping the wall thickness even. A thin joint is a weak joint.

Do all four corners the same way, and then dry a corner-molded piece slower than you would dry a round one. Seams shrink at their own rate, and a seam is where a crack starts.

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Part four · Making it beautiful

The two steps that separate a nice piece from one people ask you about.

Step 9. Press it onto the form, then trim the edge

The step everybody rushes. Do not be everybody.

A finger squish is remarkably hard to get back out, and it will still be sitting there under the glaze in three weeks. The edge does not have to be perfect, because you rasp it in step 12.

Start in the middle. Work slowly outward, stretching the clay gently over the form as you go, until the whole slab is sitting against the slab mold with nothing lifted anywhere.

Palms, not fingertips

Rock slowly with the palms of your hands. A finger squish is remarkably hard to get back out, and it will still be sitting there under the glaze in three weeks.

This is why the flaps came off first. Try to form the piece with all that weight still hanging and you will fight folds the entire way around.

Now the neat trim

Go back up to the edge you found in step 8 and follow it around softly, keeping the needle tool fairly level. Be extra careful not to scrape the slab mold here. You will rasp this edge down later, so it does not need to be perfect. You just want a good starting point.

Why this step is worth the extra minutes

Following these steps properly costs you a few more minutes per piece. That is the entire difference between a nice piece and one where people ask you where you bought it.

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Step 10. Smooth it, texture it, sign it

Where a good piece turns into a beautiful one.

Dry-finished pieces come out more pristine every time, which is why the sponge stays in the bucket. To paddle: center it on the banding wheel, find where it curves down off the flat bottom, and spin slowly while you tap your way down and around.

The red rib

Red ribs are extra soft and bend as you work, and this is where they earn their place. Work slowly over the whole surface until it is smooth, taking out the fingerprints and the rib marks as you go. Do not press too hard or you create thin spots and thick spots. Keep working it and keep it evenly compressed.

Try to use no water at all

The goal is a whole piece finished dry. If it is taking you a long time and you start seeing cracks or separation, dip the sponge, squeeze it out really well, and you can use a bit more force with it. But dry-finished pieces come out more pristine every single time.

Smooth, textured or paddled

Paddling is simple, it adds real elegance, and the thump texture is the signature on a lot of the work that leaves this studio.

  1. Center the piece on the banding wheel.
  2. Find the point where it starts to curve down from the flat bottom, because most people do not paddle the bottom.
  3. Get into a rhythm. Spin slowly and give it light taps, working your way down and around the outside.
  4. Once you reach the bottom, go faster, up and down the sides.
  5. Paddling stretches the piece slightly, so do a quick trim afterward to bring the edge back against the bottom of the slab mold.
A large finished serving bowl made on a Clay Hole slab mold, cream on the outside with a deep blue glazed interior, sitting on a stack of books by a fireplace
A serving bowl made on one of our slab molds. This is what the extra few minutes in step 9 buys you.

Your maker’s mark

Now is the stage to add it, while the clay still takes a mark cleanly. Most people scratch theirs in with a needle tool and most people put it on the bottom. There are no rules here. It is your mark, put it where you want it.

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Part five · Drying, finishing, putting away

Nearly there. This is also where a finished piece still gets lost, so do not coast.

Step 11. Dry it on the slab mold, then release it

The waiting part. It is a touch thing, not a timer.

Detaching early is so the plaster cannot catch the piece as it shrinks, which is what cracks it. Ready is when it holds its own shape lifted by the rim. A touch test, not a timer, and too long under a lamp cracks it too.

Plaster pulls water out of your clay. That is the whole reason we use it, and it is what hardens the piece enough to hold its own shape once the form is gone. So the piece has to dry on the slab mold before it comes off.

Air drying is better

If you have the time, let it dry naturally. It is always the better option and it is always the safer one.

The heat tables

If you want to speed it up, flip the switch on the lamp. Space under there is limited, so get your pieces on and off rather than parking them. Turn the mold a quarter turn every five minutes, because one side always dries faster than the other, and take the piece off the moment it holds its shape. And know that leaving it too long under a lamp dries it out and cracks it, so speeding it up can create its own problem. Last one out turns the lamps off.

Detach it early

After the first stretch of drying, pull the bottom of the piece away from the slab mold slightly and check that it is not stuck anywhere. Put even pressure on the rim and lift until it comes loose, then set it right back down.

It is not ready to come off yet. You are only detaching it, so that when the piece shrinks the plaster cannot catch it and crack it.

Knowing when it is actually ready

It is ready when you can lift it by the rim and it holds its own shape instead of folding in on itself. That is the only test.

Fifteen minutes is not the answer. Fifteen minutes worked once, for somebody else, on a different piece, in a different room.

When it passes that test, lift it carefully, because it is still fragile, and flip it over.

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Step 12. Finish the rim and put everything away

Last ten minutes. This is the part that keeps the room working.

The rasp only cuts one way, so find the sharp side first. Cotton sheet over it for Purple Level and Black Level Members, a plastic bag for Green Level and Yellow Level Members, or their own cotton sheet. Dry cloth on the slab mold, never water, never a wet cloth, never under a tap.

The rasp

Work out which side of the rasp is the sharp side, because it only cuts in one direction. Then apply even pressure all the way around the rim and even it out. Catch it at the right stage and you can smooth it perfectly with just your fingers afterward, then give it one final pass with the red rib. A damp sponge if it is really rough, but again, dry is better.

Clearing the shavings

Brush them off carefully so you do not press them into the wet clay. A good trick is to roll all the shavings into a little ball of clay and use that ball to tap the rest of them up. If they are dry enough, take them up with a barely damp sponge. Never sweep them dry or blow them off, because that puts dust back into the air you breathe.

Drying your finished piece

Upside down on a big plastic bat on your shelf. Purple Level and Black Level Members can use a cotton sheet over it, which dries it more evenly, and it will be ready by the time you come in next week. Green Level and Yellow Level Members use a plastic bag, or bring their own one hundred percent cotton sheet.

Putting the slab mold away

Dry cloth only, scrubbed well. Smooth clay residue left on the surface is completely fine. Never water, never a wet cloth, never under a tap.

Then back on the shelf in the exact spot you found it, not the nearest gap. The whole room only works because the next person can find what they need where it is supposed to be.

And clean up your mess

Table wiped, tools rinsed and returned, floor clear. Somebody is sitting at that spot tomorrow.

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The walk-through

Or watch somebody do the whole thing.

Just under fifteen minutes, one piece from choosing the slab mold to the finishing touches and cleanup. It runs in the same order as this page, so you can follow along with either one, or run both at once.

Just under fifteen minutes, one piece start to finish, in the same order as this page.

It plays right here. Watch it on YouTube instead.

Stuck halfway through a piece?

Ask. Any hand-building instructor can walk over and sort it out with you. Our main instructors wear pink shirts and our trade instructors wear purple, and there are instructors on the floor during every instructed class. Class times.

Not certified yet?

The certification covers the rules, the money side, and what actually damages a slab mold. It takes about twenty five minutes once, and then you are set for as long as you are a member. Get certified.

Starting a fresh piece?

Clear every tick and start again from step one. Nothing else on the page changes.

The Comprehensive Version has the reasons behind every step, the air bubble fix, and the full fold repair for sharp-cornered slab molds. The toggle is at the top of the page.

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