The pottery wheel · Diagnosing a throw

Something is going wrong on the wheel. Here is what to check, in order.

Find the thing your pot is doing, work down the list under it, and stop when you reach the cause. Most of these have three or four possible causes and only one of them is yours. Guessing costs you the pot. Checking costs you thirty seconds.

Twenty one problems, grouped in the order a throw happens: your body and the machine, centering, staying stuck to the wheel, the floor, the walls, and the clay itself. Each one has a short list of what to check and the order to check it in. There is also a six point check that fixes about half of them before you diagnose anything.

This is the short version: the six point check, and the seven problems that come up first. The other fourteen, the anatomy of a pot and the questions we get are in the comprehensive version.

21Problems, each with its own list of what to check
7Problems that come up first, each with its own list
6Things to check before you diagnose anything. They cover about half of this page
In orderEvery list runs top to bottom. Stop at the first thing that is off
Jump to a section
Find your symptom The check before every other check What these lists call the parts of a pot Your body and the machine Centering Staying on the wheel The opening and the floor Pulling the walls The clay and the water When to stop and reclaim it How this works at The Clay Hole Questions we actually get Related lessons
An illustration of a potter at a wheel looking down at a leaning, off center cylinder with one wall thinner than the other, water pooling in the bottom

Twenty one problems, the six point check, the anatomy of a pot, when to reclaim it, and the questions we get.

Start here

Find the thing your pot is doing.

Twenty one of them, grouped in the order a throw happens. Tap the one that looks like yours and it takes you straight to its list.

The seven that come up first. Tap the one that looks like yours and it takes you straight to its list.

Not sure which one it is? Run the six point check in the next section first. It covers about half of this page.

Your body and the machine
Centering
Staying on the wheel
The opening and the floor
Pulling the walls
The clay and the water

Before you diagnose anything

Six things to check before you change anything about your hands.

It takes about ten seconds and it is the cause of roughly half the problems further down. A beginner who is braced properly and running the wheel at the right speed for the stage has already fixed the jerking, most of the wobble and a fair share of the collapses.

  • 1Stool and wheel heightSit so your elbows land at or just above the level of the wheel head. Too low and you throw with your shoulders, and your back pays for it an hour later.
  • 2Elbows locked downLeft elbow into your hip or the top of your thigh. Right forearm braced across your thigh or against your side. An arm held out in the air has nothing behind it, and the clay wins.
  • 3Weight over your handsLean in from the hips so your body is behind the push rather than your shoulders. Sit close enough that you are not reaching for the wheel.
  • 4Hands joined into one toolThumbs crossed, or one hand stacked on the other. Two separate hands make two separate pressures, and clay reads that as an invitation.
  • 5Wheel speed matched to the stageFast for centering and opening. Slower for every pull, and slower again as the pot gets tall. Fast and tall is how pots fold.
  • 6Water enough to slide, not enough to softenA dry wall grabs and drags. A soaked wall goes slick and will not hold pressure. Wet your hands, not the pot.

If you remember one thing

Braced arms and the right wheel speed fix more beginner problems than any technique on this page. When something goes wrong, check those two before you change anything else.

The words on this page

What these lists call the parts of a pot.

Drawn to scale: a four inch mug with a quarter inch floor and a quarter inch wall, cut down the middle and sitting on a bat. Six words that turn up on every list below.

Mug cross-section on the bat, scale diagram: a thin rim first to show every error, quarter inch walls, the floor flat and thicker, outer base flat.
  • 1The rimThe thinnest, fastest part of the pot, and the first place every other error shows up. Compress it after every pull.
  • 2The wallA quarter inch is a good working thickness for a mug. Feel it between finger and thumb before each pull rather than guessing.
  • 3The profileThe line your outside hand draws as it climbs. Whatever path that hand takes is the shape you get.
  • 4The cornerWhere the floor meets the wall, on the inside. Every pull starts here, hooked under the base. A pull that starts higher leaves a shelf.
  • 5The floorAbout a quarter inch under a mug, more under a bowl that gets a foot ring. You cannot see it, so measure it with a needle tool.
  • 6The baseWhere the clay meets the bat. Sealed down with a thumb, dry underneath, and left alone until the throwing is finished.

Sitting and setup

Four problems that are really about your chair and your pedal.

Four things that hurt, or wobble, or feel wrong, and none of them are about your hands.

Your back, neck or shoulders ache after twenty minutes

Almost always the stool, not the throwing. If the wheel head sits high and your seat sits low, you end up bracing with your shoulders and holding your spine bent for the whole session. Clay does not cause back pain. Sitting wrong for two hours does.

Check, in this order0 of 6 ruled out

Your fingers, wrists or forearms hurt

Beginners squeeze. It feels like the only way to move clay, and it is the slowest way there is. Pressure on a spinning wall comes from your body leaning in through braced arms, not from your fingers gripping.

Raw fingertips are a different problem with the same look. That one is friction, and friction means there is not enough water on the wall.

Check, in this order0 of 7 ruled out

Your hands shake or drift while you are trying to hold still

A shake is an unbraced arm doing a static hold. Muscles held rigid in mid air start to tremble inside about thirty seconds, and the clay records every bit of it as a spiral up the wall.

Check, in this order0 of 6 ruled out

You cannot tell how fast the wheel should be going

There is no single right speed. There is a right speed for each stage. The rule is short: fast when the clay is low and thick, slow when it is tall and thin. Beginners get this backwards more often than any other single thing on this page.

Check, in this order0 of 6 ruled out

Getting it centered

Three ways centering goes wrong.

One way centering goes wrong, and it is the one everybody meets first.

The first wall everybody hits. Almost all of it is bracing.

The clay jerks your hands around and will not sit still

You are riding the clay instead of resisting it. An off center lump pushes your hands out once per revolution. If nothing is bracing your arms, your hands move, the pressure disappears at exactly the moment it was needed, and the lump stays as off center as it was when you started.

Check, in this order0 of 8 ruled out

You get it centered, and then it goes out again

Centering usually fails in the two seconds after it worked, or at the opening. Both are pressure problems. Coming off the lump too fast pulls it with you, and pushing down anywhere other than dead middle puts it straight back out.

Check, in this order0 of 6 ruled out

You cannot tell whether it is centered

Your eyes are the worst tool for this. A spinning lump looks smooth long before it is true, and the top of the lump lies more than the side does.

Check, in this order0 of 6 ruled out

Stuck down, or not

Two problems, and they are opposites of each other.

One problem: the pot coming loose while you throw it.

The pot coming off the bat, and the pot refusing to come off the bat.

The pot comes off the wheel head or the bat

Water is the usual answer. A film of water between the clay and the bat is a release layer, and a spinning pot only needs one weak spot to let go. The rest of the time it is a base that was never sealed down, or outward pressure at the very bottom of a pull.

More on seating a bat and getting a pot off a bare wheel head is in Bat or No Bat.

Check, in this order0 of 8 ruled out

It is stuck so hard you cannot get it off

Usually a wooden bat that has sat under a wet pot, or a pot lifted while it is still too soft to hold its own shape. Neither one is fixed by pulling harder, and pulling harder is how rims get wrecked.

The whole lift, in order, is in Getting a Pot Off the Wheel.

Check, in this order0 of 6 ruled out

Opening and the floor

Three things that go wrong in the part you cannot see.

Two things that go wrong in the part you cannot see.

Nobody can look at a floor from the top of a pot. That is the whole difficulty.

The bottom is too thick

Two causes, and they look identical from above. Either you never opened all the way down, or you started widening before you had the depth, which spreads clay across the floor with nowhere left for it to go. Nobody can see a floor from the top of a pot.

Check, in this order0 of 6 ruled out

The bottom is too thin, or you went straight through

Opening with one fingertip is a small tool putting a lot of pressure on the softest part of the pot. It goes through faster than anyone expects, and the moment before it goes through looks exactly like the moment before it does not.

If it is already too thin, there are still a few moves left in Fixing a Bottom Thrown Too Thin.

Check, in this order0 of 6 ruled out

The floor is uneven, or there is a ridge in the corner

That ridge is clay you pushed sideways when you widened the floor and then never lifted. It sits in the corner where the floor meets the wall, and it will still be sitting there after you trim, because it is on the inside where a trimming tool never goes.

Both compressions, and why they matter days later, are in Compressing the Floor and the Rim.

Check, in this order0 of 6 ruled out

Pulling the walls

Six ways a wall goes wrong on the way up.

Three ways a wall goes wrong on the way up.

Where a decent pot becomes a good one, and where most of them are lost.

The cylinder keeps turning into a bowl

The wall goes where your hands take it, and beginners take it out. Two things do it. The inside hand leading, and a pull that travels up and away instead of straight up.

A cylinder also widens a little on every single pull whether you like it or not, so part of the answer is putting it back rather than stopping it happening.

Collaring is a technique in its own right, and it is covered properly in How to Collar In.

Check, in this order0 of 7 ruled out

Thick at the bottom and thin at the top

The pull ran out of clay before it ran out of wall. Nearly always because it did not start low enough, or because it sped up as it climbed and took more from the top than it ever took from the bottom.

For the numbers a wall and a floor should actually land on, see Proportions, Ratios and Wall Thickness.

Check, in this order0 of 6 ruled out

The rim goes wobbly, uneven or ragged

The rim is the thinnest and fastest moving part of the pot, so every error on this page collects there first. It is also the easiest thing on the whole page to fix, and almost nobody does it often enough.

Leveling a rim that has gone off is its own short job: Trimming an Uneven Rim.

Check, in this order0 of 6 ruled out

The wall twists, spirals or tears

A spiral is your hands traveling faster than the clay turns underneath them. A tear is the same thing with friction added: dry clay, a fingernail or a crumb of grit dragging a line up the wall until it opens.

There is a full page on this one, including the twist that only shows up after trimming: How to Stop Pots Twisting.

Check, in this order0 of 6 ruled out

It collapses partway up

Three things do this and they compound: too much water, too many pulls, and a wheel running too fast for how tall the pot has become. The fold happens at the thinnest band, which is usually just above where your fingers slowed down.

Check, in this order0 of 6 ruled out

The pot goes lopsided partway up

Height is a magnifier. A lump that is a millimeter out at two inches wide is most of a centimeter out at six inches tall. A pot that goes lopsided halfway up was rarely centered to begin with.

Check, in this order0 of 6 ruled out

The material

Three times it is the material and not you.

Worth ruling out before you decide your hands are the problem.

Air bubbles keep turning up in the wall

Bubbles are a throwing problem, not a kiln problem. A pocket in the wall makes a thin spot, and a thin spot tears on the next pull. What actually breaks pots in a bisque firing is water trapped in a thick wall, not air.

They come from wedging, and mostly from reclaimed clay or the clay at the very bottom of a bag.

Check, in this order0 of 6 ruled out

The clay is too hard, or too soft

Clay out of a fresh bag is usually about right. Clay that has been open on a shelf goes stiff at the edges, and reclaimed clay can be either. Neither one is something to power through. Hard clay hurts your hands and soft clay will not stand up.

The full set of methods is in Softening Hard, Stiff Clay.

Check, in this order0 of 6 ruled out

Everything is soaked and the wall will not hold anything

Beginners use about four times as much water as they need. Water is a lubricant, not a material. Once the wall has drunk it, the clay has lost its structure and there is nothing to do but wait.

Ribs do more of this job than most beginners realize: Using Ribs While You Throw.

Check, in this order0 of 6 ruled out

Knowing when to stop

Some of these pots are not coming back, and knowing which is a skill of its own.

Some of these pots are not coming back.

A pot that is slightly off center, or has a rim you can level, or has one wall thicker than the other, is worth finishing. You will learn more from finishing it than from a fresh lump, because finishing is the part you are short on. A pot that has torn, folded, lost its floor or gone to slip is finished. Wire it off, put the clay in the reclaim, and take a new ball.

The reason to make that call quickly is that you have a limited number of good pulls in your hands each session. Spend nine of them on a pot that was never going to make it and the next one, which would have been fine, gets thrown with tired hands at the end of the night. Nobody counts that and everybody feels it.

If it is worth saving but you are not sure how, Rescuing Pottery at Any Stage runs through what is still possible at every point between wet clay and a fired glaze.

Small problems are worth finishing, because finishing is the part you are short on. A pot that has torn, folded or gone to slip is finished, and the fastest thing you can do is wire it off and start again. You have a limited number of good pulls in your hands each session, and spending them on a lost pot costs you the next one.

Change one thing, then throw again. Four changes at once and a pot that works has taught you nothing.

How it works here

How this works at The Clay Hole.

This page is written for potters everywhere. Here is where our studio stands.

Four things to know here

Twenty nine wheels, first come and first served, and the wheel video is required before you throw. Bats are free on the racks with no level gate, and wood is the right default. Green Level Members bring their own tools and a sponge, and every level above that has tools waiting. If something is going wrong, find a pink shirt or a purple one and ask them to watch you throw for two minutes.

The wheels

Twenty nine of them: twenty four electric and one kick wheel in the main throwing area, and four more in the Black Level overflow. First come, first served, and every wheel is open to every level.

Watch the wheel video first

It is required before you throw, experienced potters included, because it covers how things run here rather than how to make pottery.

Bats

Round wood and MDF, round plastic, and square. They live on the racks, they are free, and there is no level gate on them. Wood is the right default. Plastic never lets go on its own, so wire a pot loose before you leave.

Ask a pink shirt

Our main instructors wear bright pink tees and our trade instructors wear purple. Either one will stand and watch you throw for two minutes, which beats twenty minutes of guessing on your own.

Tools

Green Level Members bring their own basic set and a sponge. Every level above that has tools waiting, ribs and needle tools and wires included.

The clay

Eight clay bodies here, all light or medium, all glaze fired to cone 5½. If a bag feels wrong, swap it rather than fighting it for an hour.

Questions we actually get

Six that come up at the wheel.

How long before centering stops being a fight?

For most people it is several sessions rather than several minutes. The thing that changes is not strength, it is bracing. The night it clicks, it usually clicks in about ten seconds and never fully goes away again.

Is it my clay, or is it me?

Nine times out of ten it is bracing or wheel speed. Clay is worth suspecting when it is visibly dry at the edges, or when it came out of a reclaim bin. Wedge it and cut it in half before you blame it.

Should I be using tools or my hands?

Hands first, for the first few months. A rib will make a better wall than your fingers will, and it will also hide what your fingers are doing wrong. Learn to feel the wall, then add the rib.

How much clay should a beginner start with?

Around a pound to a pound and a half. Most people start too big, spend the whole session fighting the centering, and never reach the part they came for.

My pot looks fine and then it cracks a week later. Is that a throwing problem?

Often, yes. A floor that was never compressed, or a base much thicker than the walls, cracks days later while it dries. That is the throw showing up late rather than the drying going wrong.

Everybody else looks like they know what they are doing.

They are also making bad pots. The difference is that an experienced potter wires a bad pot off in about two seconds and starts again, so you never see it happen.

Related lessons

Six lessons that sit next to this one.

Three to read next.

This page is a diagnosis page. These are the pages that teach the moves it keeps pointing at.

The pottery wheelHow to Throw on the Pottery WheelThe whole throw, start to finish, in the order it happens. The pottery wheelOpening the Clay and Setting the FloorWhere the floor problems on this page get solved properly. The pottery wheelCompressing the Floor and the RimTwo compressions that prevent about half of this page. The pottery wheelBat or No BatSeating a bat, and lifting a pot off a bare wheel head. The pottery wheelHow to Collar InThe fix for a cylinder that keeps widening on you. The pottery wheelProportions, Ratios and Wall ThicknessHow thick a wall and a floor should actually be.

The whole point

Find the cause, then change one thing.

This is a set of lists rather than a set of tips because beginners change four things at once, the pot works, and they learn nothing from it. Work down a list, stop at the first thing that is off, change that one thing, and throw again. If the pot still does the same thing, go back to the list and keep going. Ten minutes of that is worth a month of guessing.

Work down the list, stop at the first thing that is off, change that one thing, and throw again. The other fourteen problems, the anatomy of a pot and the questions we get are in the comprehensive version at the top.

How to Throw on the Pottery Wheel Compressing the Floor and the Rim

Written for potters everywhere. Where our studio does things differently, the page says so.