Required training · Slab rollers and molds

Get certified for the slab rollers and molds.

Molds are the shortcut nobody tells you about. A serving bowl that would take years of practice to throw on the wheel, you can make properly on your first day.

More than 150 of them live in the mold room, plaster and wood, and every one is fragile and expensive. So everybody learns the same way first: watch the video, agree to the rules, sign for them. At the end you save a certification card with your name on it.

Takes about 25 minutes, and 15 of those are the video.Do it once and you are certified for as long as you are a member.

The Clay Hole mold room: steel shelving racks filled with white plaster dome and trough molds, each marked with a colored dot.
Why we are this careful about the molds

A mold is not a machine. It is a soft block of plaster, or a piece of soft wood, and both of them absorb water and both of them mark, chip and crack if you handle them the way you would handle a tool.

The damage is also quiet. Drag a needle tool across plaster and nothing looks wrong. What happens is that a few specks of plaster end up in the clay, and two weeks later somebody’s bowl splits down the middle in the kiln. Meanwhile the mold has a groove in it that every future piece will copy.

So we would rather spend 25 minutes with you once than lose molds one at a time. Small ones start around $40 and the big Black Level ones run past $600, and some of them we simply cannot buy again.

Before the rules, the good part

A bowl that takes years on the wheel, on your first day.

Throwing a bowl this big takes years of practice and a lot of clay, and even then plenty of them collapse. On a mold you get the same form, clean and even, right away.

The other thing molds give you is company. Slab work happens at the pottery tables, not tucked away at a wheel, so you spend the evening making something beautiful while you are actually talking to people.

A large mold-made serving bowl, bare Berlin Gray clay on the outside and a deep mottled blue glaze inside.
Made on a mold and paddled for that thump texture. Bare Berlin Gray on the outside, blue inside.
Three nested oval dishes in graduating sizes, glazed oatmeal and soft brown with warm tan breaking over the rims.
Three sizes off three molds. Nesting sets are one of the things molds do that a wheel really cannot.

The slab rollers are open to every level. Both of them, and they will roll a slab up to 30 inches. The molds are the part that steps up with your membership color, and the sticker underneath each one tells you which.

The certification

Let’s get you signed off.

Five steps, about 25 minutes, and most of that is the video. At the end you save a certification card with your name on it.

Step 1 of 5

First, who are we certifying?

Use the name you signed up with, spelled the way you would want it printed on your certification card.

The written guide

Everything, spelled out.

The video is the training. This is for the evening you are standing at the roller trying to remember how thick the slab was meant to be.

Choosing your mold

The color sticker is the whole system

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

  • GreenGreen molds only. The smaller forms.
  • YellowGreen and yellow.
  • PurpleGreen, yellow and purple.
  • BlackEverything, including the giants.

As a rule, bigger means higher

The bigger and more expensive the mold, the higher the level needed to use it. Almost all of them are open to you by Purple Level.

Plaster and wood

Most of the molds are plaster. There are also plenty of wooden ones now. The wood is soft and absorbs water the same way plaster does, and it is just as sensitive, so every rule on this page applies to both without exception.

Sharp corners are the difficult ones

Clay will not drape neatly over a sharp corner. You end up with folds that have to be cut away and mended back together, which takes more time and more practice. Every other shape is designed to have a slab laid straight over it and will look beautiful with very little effort.

One at a time

Take one mold out of the room at a time. Once you are experienced you can run two or three pieces at once if you want to, but dip your toes in first, figure out the rhythm, then expand.

Remember where it lives

Take a mental note of exactly where you lifted it off the shelf, because that is where it has to go back. If you know you will not remember, take a photo on your phone. Nobody will judge you for it.

Setting up your station

Every mold sits on a banding wheel

You want something that sits nicely underneath the mold without digging into it. Most of our molds work fine on the little banding wheels.

Flat bottom, concave bottom

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

The tools you need

  • A wire cutter, for cutting your clay off the block.
  • A soft red rib. These bend as you work and they are what gets your surface pristine. Green Level Members bring their own tool set; every other level can use the studio red ribs.
  • A pottery sponge. The yellow ones are great for mold work.
  • Either a wooden potter’s knife or a needle tool.

Knife or needle tool

The needle tool cuts noticeably nicer and easier, but it can shave plaster off your mold if you are careless with it. The wooden potter’s knife is the safe option and it is almost as good. It is a genuine preference, as long as you know what you are trading.

How much clay, and how thick

Thickness

A third of an inch is right for a mold around 13 inches across or smaller. Half an inch is the sweet spot for anything bigger than that. Those numbers are for wet clay, and they leave you enough to paddle, texture stamp or add embellishments without going through.

Do not go thinner to save clay. The thinner the slab, the more likely it warps in the kiln.

How much clay that means

For a 13 and a half inch mold at half an inch thick, that is roughly 8 pounds, or about a third of a bag. Close enough is usually good enough, and most of the trimmings go straight back into your bag for the next piece.

Width

Measure the widest point of your mold and add at least half an inch, preferably a full inch. So a 13 and a half inch mold wants a slab about 14 and a half to 15 inches at its narrowest point. Work this out before you start rolling, not after you carry the slab over.

Do you need to wedge it?

If it is coming straight out of a fresh bag, no. Fresh clay comes out of a pug mill already wedged, with no air bubbles in it, and it is going straight through the slab roller anyway. If you want it softer and more workable, wedge it. There is no wrong answer.

Getting the block under three inches

Whatever you do, the block has to be under three inches tall before it goes on the roller. Slam it on the table at an angle, rotate, slam again. It stretches out sideways and shortens as you go.

Rolling the slab

The setup

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 with every pass.

Read the gauge properly

This is the single most common mistake. The main marks are quarter inches and the marks next to them are eighths, not quarters. Read them as all quarters and you will end up nowhere near the thickness you meant to hit.

Also worth knowing: the lower the bar goes, the more each increment stretches the clay. A quarter inch change at the start barely does anything. 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 it is all the way through and there is no tension left.

If the wheel is really hard to turn, you have lowered the bar too far. Raise it back up. 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 90 degrees as you go to keep the shape square, and keep it centered on the mats. Square is what you want, because that is the shape you are draping over a round 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 final pass

Adjust to exactly half an inch, remembering that the half inch includes the thickness of the mats, so you are really landing a little under. On the last pass, send it through both ways.

Getting it off the mat

Pull the top mat off, then peel the bottom one back slowly. If you yank the clay, the whole mat comes up with it. Slow hands.

Air bubbles

You will get one eventually, especially with clay you have wedged yourself or scraps from other pieces. Grab an instructor and they will show you how to get them out. It is not hard at all.

Getting it onto the mold

Trim it round first

One side is almost always longer than the other. Come in with your needle tool and shave the extra off so it is closer to a circle. It will drape over the mold far more easily. Wedge the 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 the firing brings it back out. Keep the slab as flat as you can, move it slowly, drape it slowly.

Picking it up

Handle it very carefully here. If you squeeze it you get fingerprints all through the piece and they take a lot of work to remove. Hold it between your fingers and your palm and lift it off the mat that way.

The drape

Hang the slab down until you can see the bottom edge of it below the edge of the mold, then very slowly drape it across. If it lands off center, lift and shift it. You want the flaps and frills of clay reasonably even all the way around.

Trimming and forming

Find the edge of the mold

Take your needle tool and run it straight up against the mold until you feel it stop at the bottom edge. That is where your final cut will be. Not yet, though.

First, cut the big flaps off. Straight sideways.

Listen carefully to this one, because it is the whole trick. Cut straight sideways. Then adjust, so the cut part comes away and the next part 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. And do not push into the mold while you slice.

You are not trying to get a clean finished edge at this stage. You are just getting rid of the extra weight that is dragging the clay down.

Now press it onto the form

Do not rush this. Start in the middle, then slowly work your way out toward the outside, stretching the clay gently over the mold as you go.

Use the palms of your hands, rocking slowly. Not your fingertips. A finger squish is remarkably hard to get back out.

This is why you cut the flaps off first. Try to form it with all that extra clay still hanging and you will fight folds the whole way. Following these steps takes a few extra minutes per piece and it is the difference between a nice piece and a genuinely professional one.

The final trim

Go up to the edge again and very softly follow it around, keeping the needle tool fairly level. Be extra careful not to scrape the mold here. You will rasp this edge down later, so it does not have to be perfect. You just want a good starting point.

Smoothing, texture and your maker’s mark

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 will create thin spots and thick spots. Keep working it and keep it evenly compressed.

Try to stay dry

The goal is to get to where you use no water at all. If it is taking you a long time and you start getting cracks or separation, dip your sponge, squeeze it out really well, and you can use a bit more force. But dry-finished pieces always come out more pristine.

Paddling, and the thump texture

Once it is smooth you can decide: smooth, textured, or paddled. Paddling is simple and it adds a real elegance, and the thump texture is the signature on a lot of the work that comes out of this studio.

Center the piece on the banding wheel and find the point where it starts to curve down from the flat bottom, because most people do not paddle the bottom. Then get into a rhythm: spin slowly and give it light taps, working your way down and around the outside. Once you reach the bottom you can go faster, up and down the sides.

Paddling stretches the piece slightly, so do a quick trim afterward to bring the edge back against the bottom of the mold.

Your maker’s mark

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

Drying and getting it off the mold

Why plaster works

Plaster pulls water out of your clay, which is what hardens the piece and lets it hold its shape. The clay has to dry enough on the mold that it keeps its form when it comes off.

Air drying is better

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

The heat tables and lamps

If you want to speed it up, we have heat tables. Flip the switch on the lamp to turn it on. Space under them is limited, so get your pieces on and off quickly rather than parking them there. Rotate the piece 180 degrees from time to time, because one side always dries faster than the other. And be aware that leaving it too long under a lamp will dry it out and crack it, so speeding it up can create its own problems. Turn the lamps off if nothing else is under them.

Detach it early

After the first stretch of drying, pull the bottom of the piece away from the mold slightly and make sure it is not stuck anywhere. Put even pressure on the rim and lift until it comes loose. It is not ready to take off yet, you are just detaching it, so that when it shrinks the plaster cannot catch it and crack it.

Knowing when it is ready

This is a touch thing, not a timed thing. It is ready when you can lift it by the rim and it holds its shape instead of folding in on itself. Then lift carefully, because it is still fragile, and flip it over.

Finishing the rim and putting everything away

The rasp

Work out which side of the rasp is the sharp side, because it only cuts in one direction. Then apply even pressure 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 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 neat trick is to roll all the shavings into a little ball of clay and use that to tap the rest up. If they are dry enough, a dust brush works too.

Drying your finished piece

Put it 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 plastic sheets.

Then put your molds away

Clean up your mess, and put the mold back in the exact spot you found it. Dry cloth only, and a smooth clay residue left behind is completely fine.

The rules in one place

Never

  • Never put heat on a mold.Plaster cracks, and the wooden molds are just as sensitive.
  • Never scrape a sharp tool against a mold.Particles get into your clay, your piece cracks in the kiln, and the mold is damaged for good.
  • Never cut down into a mold while trimming.Straight sideways, always.
  • Never clean a mold with water or a wet cloth.Dry cloth, scrubbed well.
  • Never knock a mold on a hard edge.Most damage happens going on and off the shelves.
  • Never force the slab roller wheel.Hard to turn means the bar is too low. Raise it.
  • Never use a mold above your membership color.The sticker underneath tells you.

Always

  • Always check the sticker before you lift it.Your color or below, never above.
  • Always take one mold at a time.Until you are experienced with them.
  • Always note where it came from.A photo on your phone is a perfectly good memory.
  • Always rotate the slab 90 degrees between passes.Clay only stretches side to side.
  • Always move clay flat and slowly.Clay has a memory and the kiln reveals it.
  • Always press from the center outward with your palms.Never fingertips, never rushed.
  • Always detach the piece from the mold early.So shrinkage cannot crack it.
  • Always put the mold back in its exact spot.And clean up after yourself.
What happens if a mold gets broken

Members are responsible for the cost of a mold broken through accident or carelessness, and for damage caused by breaking the rules above, such as taking a sharp tool to one.

Normal wear and tear is never charged to a member. Molds age, and that is our cost, not yours.

To give you a sense of the numbers: small molds start around $40 to replace. Most of the big ones are under $200. The largest Black Level molds run past $600, and a few of them we would struggle to buy again at any price.

None of this is meant to make you nervous about using them. Follow the rules on this page and the odds of any of it applying to you are tiny. We would just rather you knew the stakes than found out about them afterward.

The honest numbers

Why the fuss over a lump of plaster.

Because it is not a lump of plaster, it is a shelf full of them, and they are the reason a beginner can make something beautiful on day one.

150+Molds in the roomPlaster and wood, from small Green Level forms up to the giants.
$40 to $600+To replace oneMost of the big ones are under $200. A few cannot be replaced at all.
2Slab rollersBoth open to every level, and both will roll a slab up to 30 inches.

Wear and tear is on us. Breakage is not. Molds get old and that is our cost. A mold broken through carelessness, or damaged by a sharp tool, is replaced by the member who did it.

Take care of them and they will be here in ten years.

Dry cloth. No heat. No sharp tools. Straight back on the shelf where you found it. That is genuinely most of it, and the rest of the video is just how to make a really good piece.