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Joel Cobbar

Clay Becomes Off-Center When Opening

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Hey all, brand new here so I'm not sure about tags, etiquette, or if this is the right place for questions so feel free to correct any errors on my part.

So, I have been practicing throwing at every opportunity for the last couple of months. I have been taking a general ceramics class, but the teacher is really a handbuilding person and the throwing stuff is mostly left as a "do it if you want to" sort of thing, and they leave the throwing students to their own devices. As a result, I am almost entirely self-taught, and learned almost everything I know about throwing from this guy - https://www.youtube.com/channel/UCjqCOLOIp8HKkBxBuiQFTdw, and this guy https://www.youtube.com/channel/UCTkXls_DXtwl9f2lt5qmosw. I'm certainly much better than I was when I started, I can center relatively quickly and I can throw bowls and mugs with little difficulty. Lately however I have been having trouble with the clay appearing centered, but then when I start to open it, or push the floor out the walls start to oscillate.

I open by pushing my thumb straight down into the center of the clay, before angling my thumb to push the hole out into a cone shape and then using my fingers to widen the base. Somewhere in this process is when the oscillation starts. It's not so bad that I can't do anything with the clay, I can still make the aforementioned bowl or mug but anything more complex like a vase tends to fall apart, not to mention it tends to mar the look of the piece. Sometimes, I can force the oscillation to the top of the wall and then cut it off, but this seems like more of a temporary solution. What could be causing this, and what can I do to prevent it?

Edit: I felt I should mention that during the opening process, I keep my off-hand applying light pressure on the outside of the clay.

Edited by Joel Cobbar

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There are so many examples of how to open that it is impossible to say that there is a wrong way to do it.  So I will tell you how I do it and how my wife with weak and problematic hands does it.  I open with the speed still fairly high.  lots of water/slip to keep everything from grabbing.  Make sure if you feel anything start to grab that you make it slippery again.  I go in with both thumbs and then open moving my thumbs to each side with even pressure.  And I occasionally mess up this way and induce a wobble.   My wife opens with what could be called the hooked fingers or Claw method.  she presses down with the first two fingers of the right hand and when she gets down to the point where the floor of the pot will be she forms a c shape with her fingers and pulls the bottom straight toward her belly button till she has the bottom as wide as she is going to make it .  This leaves an under cut on the inside of the work.  Then, as she keeps her finger tips on the clay in the groove, she straightens her fingers and that brings the rest of the clay out to the same place as her finger tips.  Then she slows the wheel, compresses the bottom and starts to lift.  She got this from a video that she saw (the clay lady maybe?)  If I am having trouble keeping things even I do this as well.

 

Found it, This is where my wife saw her example.  

 

Edited by Viking Potter

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If you haven't centered the clay well, it will wobble no matter how you open it. Make sure that when you're coning the clay during centering that the bottom of the cone is reducing in diameter as you cone it up. If not, the clay down there isn't getting centered properly and will remain uneven, and will cause wobbles as you open. Centering is as much about the condition of the clay as it is the location on the wheel. Every bit of it needs to be smooth and homogenous.

If you're clay is centered properly, there's no reason at all to keep a hand on the outside of the clay while opening. You'll gain a lot more stability during opening if you have both hands locked together instead. Here's the hand position I teach:

1. Stick out your index finger on your dominant hand.

2. With your other hand, make an 'L' out of your thumb and index finger.

3. Lay the 'L' on top of the other hand, so the index fingers are stacked, dominant hand on bottom.

4. Rest on your elbows. Super important!

This is a very stable position. Your hands are locked together, and your arms are locked to your legs. Lots of bracing. Find the center of the clay and make the hole. As you go down, don't go straight down with the tip of your finger. It's much easier to drift off center if you do it that way, and you can't see how deep you're going. Instead, angle your fingers back slightly so you make a 'V' shaped hole, a little more onto the pad of your finger.

I do not teach opening with thumbs, because thumbs are short. At some point you have to switch to fingers as you get into larger pieces, so I teach fingers from the beginning. Also, as you get into really big pieces, it's an easy transition to switch from fingers to going in with your whole hand.

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1 hour ago, neilestrick said:

You'll gain a lot more stability during opening if you have both hands locked together instead.

This is what I came here to say. Your two hands working together have much more stability. Also, when opening a floor, your two hands should be addressing the same degree (out of 360 degrees) of the pot. If your hands are in two different places, you might be sending your pot two different messages and throwing it off center. 

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Try the above suggestions first. If you're still experiencing difficulties, the second most common culprit of your piece going off centre is air bubbles that get caught under the clay when you attach it to the wheel head.  To ensure that you're not doing this, really make sure that the underside of the piece is a smooth ball shape with no creases before you smack it down. An air bubble trapped in this way will ensure that the clay won't stay centred, and even if you manage to muscle through, you'll wind up with an uneven rim. 

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I started looking to make sure I was centering properly, and noticed that even though the clay feels centered it always has a very slight wobble. What am I doing to cause a very small wobble no matter how much I center it?

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37 minutes ago, Joel Cobbar said:

I started looking to make sure I was centering properly, and noticed that even though the clay feels centered it always has a very slight wobble. What am I doing to cause a very small wobble no matter how much I center it?

The most common issue I see with new throwers is a lack of bracing throughout the arms+core+legs+feet. Use your entire body. 

There is a FREE video on my website (link in my signature, then go to the “school” page) where I demo my method of centering, including lots of tips that are geared for new throwers. Keep in mind there are plenty of correct ways to center, my method is just one method. You should try various methods to find the one that works best for you.

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42 minutes ago, Joel Cobbar said:

I started looking to make sure I was centering properly, and noticed that even though the clay feels centered it always has a very slight wobble. What am I doing to cause a very small wobble no matter how much I center it?

You might be releasing pressure too quickly. If everything else is good, and it feels smooth and consistent and well mixed, and is perfectly centered when your hands are on it, releasing your hands too quickly will cause a wobble.

If, when you open, the wobble gets worse as you get deeper in to the clay, that's a problem with the bottom not being coned in narrow enough during the coning process.

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1 hour ago, neilestrick said:

You might be releasing pressure too quickly. If everything else is good, and it feels smooth and consistent and well mixed, and is perfectly centered when your hands are on it, releasing your hands too quickly will cause a wobble.

If, when you open, the wobble gets worse as you get deeper in to the clay, that's a problem with the bottom not being coned in narrow enough during the coning process.

That did occur to me and earlier today I tried taking my hands off very slowly and carefully, but the wobble persisted.

 

1 hour ago, GEP said:

The most common issue I see with new throwers is a lack of bracing throughout the arms+core+legs+feet. Use your entire body. 

There is a FREE video on my website (link in my signature, then go to the “school” page) where I demo my method of centering, including lots of tips that are geared for new throwers. Keep in mind there are plenty of correct ways to center, my method is just one method. You should try various methods to find the one that works best for you.

I thought the problem could be posture or bracing and I'm far from an expert on what proper bracing should feel like. I place my elbows on my knees while leaning forward, and hold my knees in place with the rest of my body. I tend to use my upper body weight to apply pressure to clay during centering rather than my arms. 

I don't know if it's relevant, but the clay will usually leave a wide skirt of clay on the bat, about 1-2 inches at the farthest point from the base of the actual lump of clay.

Edited by Joel Cobbar

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30 minutes ago, Joel Cobbar said:

I don't know if it's relevant, but the clay will usually leave a wide skirt of clay on the bat, about 1-2 inches at the farthest point from the base of the actual lump of clay.

Yes, this is relevant. The "skirt" or "buttress" is made of soft clay, and might not be centered or level. If your hand is resting on an unlevel buttress, the unlevel-ness is transferring to the rest of your clay. Your hand should be resting directly against the wheelhead (or batt), which is a nice solid level surface. To prevent a buttress from forming, your outside hand should be pushing down hard against the wheelhead while also pushing in. Down and in at the same time. 

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also self taught and i had a problem a with a slightly different solution.  i had trouble finding where the center of the mass of clay was.  was shown by mea rhee how to spiral my thumb into the center of the mass and let it ride for a revolution or two to see exactly where to open.   this was covered in one of the books i had years ago but i forgot about it and had a thick side and a thin side because i did not open in the true center.

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21 hours ago, Joel Cobbar said:

That did occur to me and earlier today I tried taking my hands off very slowly and carefully, but the wobble persisted.

 

I thought the problem could be posture or bracing and I'm far from an expert on what proper bracing should feel like. I place my elbows on my knees while leaning forward, and hold my knees in place with the rest of my body. I tend to use my upper body weight to apply pressure to clay during centering rather than my arms. 

I don't know if it's relevant, but the clay will usually leave a wide skirt of clay on the bat, about 1-2 inches at the farthest point from the base of the actual lump of clay.

I cant center this way, I still get the clay moving my hands, hands moving the arms, arms moving the knee, knee moving the leg.  I make sure my elbows are tucked into my hip or pelvis area so that the clay has to move my hand/arm/hip/butt/stool/concrete floor.  

Edited by Viking Potter

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Every time I have engaged in trouble shooting how/why an "off center" occurs while throwing, the RCA (Root Cause Analysis) turns up a step where the potter is moving the hands outward (or upward) faster than the clay is turning around.  Restated:  the potter is either opening (or lifting) too fast for the wheel speed, or the wheel speed is too slow for the opening (or lifting) rate.  
LT

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I have had this issue as I started to throw larger pieces and there's a number of things that I have noticed:  

  1. Clay should be well wedged and same consistency.   A hard piece will throw off your hand when you open.  An air bubble can do the same thing.  
  2. The angle of the dangle matters.   if you go straight down (75-90 degrees from the wheel head), the clay will torque your finger and you'll get an offset opening.  Make sure that your hand is going down at about 30-60 degrees to the wheel head and pull back towards yourself as you go.  
  3. Speed matters.  If you go too fast, its easier to wrong fast.   Slow down the wheel head a bit and slow down your hands.  
  4. Someone mentioned bracing, you can never be too braced or stiff. 
  5. Slow and steady wins the race.   Opening in one pass is an advanced technique.  Go a bit at a time
  6.  I have found that using my thumb to create a solid dip in the center of the clay helps to guide as I open.   For smaller pieces, I might open only with my thumb, for larger ones, I'll use my thumb, put the heel of my hand down on it and push out to about 10-11 on the clock....but that's for 20-30#.

There are some other techniques for centering that are good....coning the clay up and down a few times can center almost any clay as long as it will move in your hands.   I saw someone speak about centering not the entire ball of clay, but one slice at a time.....center the first 1/2 inch of clay on the wheel, then come up to the next 1/2 inch and center that next, and so on.  

But the number one thing that I see learners (women in particular) do when learning is not moving in on the clay.   To move the clay, you have to provide an immoveable shape for it to comply with.   lines of force from your body need to move in a straight line to the center of the clay.   When centering, your left hand (assuming your counterclockwise) should be lined up tip of the thumb, base of the thumb, wrist, elbow in a straight line as a push.  The right hand will be more of a pull through the center of the clay toward your left hand, still keeping your arm lined up the same way.   Those elbows should be tucked into your knee or thigh to brace, and the legs should be in a square stance that is stable.   

Finally, I would recommend taking a workshop from a thrower, not a handbuilder.   You'll learn SO MUCH. 

Edited by Ceallach

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