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The pottery wheel · Diagnosing a throw
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.
Start here
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.
Before you diagnose anything
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.
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
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.
Sitting and setup
Four things that hurt, or wobble, or feel wrong, and none of them are about your hands.
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.
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.
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.
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.
Getting it centered
The first wall everybody hits. Almost all of it is bracing.
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.
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.
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.
Stuck down, or not
The pot coming off the bat, and the pot refusing to come off 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.
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.
Opening and the floor
Nobody can look at a floor from the top of a pot. That is the whole difficulty.
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.
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.
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.
Pulling the walls
Where a decent pot becomes a good one, and where most of them are lost.
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.
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.
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.
Levelling a rim that has gone off is its own short job: Trimming an Uneven Rim.
A spiral is your hands travelling 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.
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.
Height is a magnifier. A lump that is a millimetre out at two inches wide is most of a centimetre out at six inches tall. A pot that goes lopsided halfway up was rarely centered to begin with.
The material
Worth ruling out before you decide your hands are the problem.
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.
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.
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 realise: Using Ribs While You Throw.
The honest part
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
This page is written for potters everywhere. Here is where our studio stands.
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.
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.
It is required before you throw, experienced potters included, because it covers how things run here rather than how to make pottery.
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.
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.
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.
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
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.
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.
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.
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.
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.
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
This page is a diagnosis page. These are the pages that teach the moves it keeps pointing at.
The whole point
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.
Written for potters everywhere. Where our studio does things differently, the page says so.
Both print clean. Every checklist comes out as empty boxes you can work down with a pencil at the wheel.
