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dm5cents

Help Needed

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I am pretty new at pottery. I love to work on the wheel, but lately I have become rather frustrated with the bowls I have made cracking at the bottom. I was told to run your finger back and forth across the bottom and have done this...still cracking. Could someone please help!

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If it is across the floor of the pot, use a rib to recompress before you cut it off with a wire. Make sure you are not going too thin. Strive for even thickness. If the walls and foot are thick and the bottom is thin OR of you used a lot of water and it sat in the bottom, you can get cracking.

Make some practice bowls, and cut them in half, wedge them up again. Check your thickness.

Marcia

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If it is across the floor of the pot, use a rib to recompress before you cut it off with a wire. Make sure you are not going too thin. Strive for even thickness. If the walls and foot are thick and the bottom is thin OR of you used a lot of water and it sat in the bottom, you can get cracking.

Make some practice bowls, and cut them in half, wedge them up again. Check your thickness.

Marcia

 

 

ty. I do have alot of water on the bottom during the

throwing, but I dry it up in the end. My bottom's are always thicker than my walls...could the weight of the walls pulling do this? On my last bowl, I used a rib on the bottom over and over again...still cracked. I will try and use less water. ty Marcia.

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I am pretty new at pottery. I love to work on the wheel, but lately I have become rather frustrated with the bowls I have made cracking at the bottom. I was told to run your finger back and forth across the bottom and have done this...still cracking. Could someone please help!

 

 

What is the shape of the carack, "S" shaped, or around the edge of the foot ring in a crescent? Is it one crack, or a few short ones?

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post-3341-1294521158924_thumb.jpg

 

I am pretty new at pottery. I love to work on the wheel, but lately I have become rather frustrated with the bowls I have made cracking at the bottom. I was told to run your finger back and forth across the bottom and have done this...still cracking. Could someone please help!

 

 

What is the shape of the carack, "S" shaped, or around the edge of the foot ring in a crescent? Is it one crack, or a few short ones?

 

 

 

I've attached a copy of the one bowl that I put patch stuff from the pottery store in...not so pretty.

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post-3341-1294521158924_thumb.jpg

 

I am pretty new at pottery. I love to work on the wheel, but lately I have become rather frustrated with the bowls I have made cracking at the bottom. I was told to run your finger back and forth across the bottom and have done this...still cracking. Could someone please help!

 

 

What is the shape of the carack, "S" shaped, or around the edge of the foot ring in a crescent? Is it one crack, or a few short ones?

 

 

 

I've attached a copy of the one bowl that I put patch stuff from the pottery store in...not so pretty.

 

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Looking at the photo, it appears that the bottom is much thinner than the sides. I think Marcia's suggestions (uniform thickness and less throwing water standing in the bottom while you throw) will solve it for you.

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As much as it hurts to do this when you are new ... a good exercise is to throw cylinders

then slice them in half to see what you are doing. Once you can throw a uniform thickness

cylinder about eight to ten inches high you move on to bowls.

 

Compress those bottoms. Level the rim and soak up the water after every pull.

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when you go to trim, put a thumb tack in the inside bottom of your bowl. Then flip over, center and start trimming. When you hit the point of the thumb tack, you'll know how thick the bottom is. I think the stem of a thumb tack is too thick, but it is a start for getting yourself familiar with the feel of the thickness of your work.

Marcia

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As much as it hurts to do this when you are new ... a good exercise is to throw cylinders

then slice them in half to see what you are doing. Once you can throw a uniform thickness

cylinder about eight to ten inches high you move on to bowls.

 

Compress those bottoms. Level the rim and soak up the water after every pull.

 

 

I agree with Chris my throwing teachers told us to think compression, compression, compression while we were throwing and spent our first year throwing and cutting up cylinders and bowls. We only got to glaze three pieces at the end of the class. I had another professor that taught us to throw with just the water that was on our hands, no water on the piece and clay was fairly soft. He would throw two foot platters in a few minutes this way, it was a thing of beauty to watch him throw. Don't give up keep practicing and you'll get it. Denice (Wichita, KS)

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As much as it hurts to do this when you are new ... a good exercise is to throw cylinders

then slice them in half to see what you are doing. Once you can throw a uniform thickness

cylinder about eight to ten inches high you move on to bowls.

 

Compress those bottoms. Level the rim and soak up the water after every pull.

 

 

I agree with Chris my throwing teachers told us to think compression, compression, compression while we were throwing and spent our first year throwing and cutting up cylinders and bowls. We only got to glaze three pieces at the end of the class. I had another professor that taught us to throw with just the water that was on our hands, no water on the piece and clay was fairly soft. He would throw two foot platters in a few minutes this way, it was a thing of beauty to watch him throw. Don't give up keep practicing and you'll get it. Denice (Wichita, KS)

 

 

Yep, after looking at the crack, which is quite familiar. I looked it up in Hamer's Potters Dictionary. Page 80 shows the crack occurring in greenware, and bisqueware, and glazeware. In your case since you had patched the work before or after the bisquefire-Hamer says in so many words that it is because of - floor being thinner than the walls when thrown, overly wet, or drying too quickly. If the crack occurs after bisque-Hamer says it was probably unnoticed in the greenware. If the crack occurs after the glaze, it is because of glaze fit, or too thin of a base where compression of glaze and clay comes into play.

 

If this is the case, I highly recommend that you refrain from using a sponge in the later stages of throwing. The sponge just puts too much water into the clay. At the same time slow your drying time of the pieces before you trim them. You have said that you use a rib to compress, but are you compressing or are you scraping the wall shape. Two different things. A rib laid at an angle on the clay will push the particles together, where as a rib held perpendicular will not.

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As much as it hurts to do this when you are new ... a good exercise is to throw cylinders

then slice them in half to see what you are doing. Once you can throw a uniform thickness

cylinder about eight to ten inches high you move on to bowls.

 

Compress those bottoms. Level the rim and soak up the water after every pull.

 

 

I agree with Chris my throwing teachers told us to think compression, compression, compression while we were throwing and spent our first year throwing and cutting up cylinders and bowls. We only got to glaze three pieces at the end of the class. I had another professor that taught us to throw with just the water that was on our hands, no water on the piece and clay was fairly soft. He would throw two foot platters in a few minutes this way, it was a thing of beauty to watch him throw. Don't give up keep practicing and you'll get it. Denice (Wichita, KS)

 

 

 

Yep, after looking at the crack, which is quite familiar. I looked it up in Hamer's Potters Dictionary. Page 80 shows the crack occurring in greenware, and bisqueware, and glazeware. In your case since you had patched the work before or after the bisquefire-Hamer says in so many words that it is because of - floor being thinner than the walls when thrown, overly wet, or drying too quickly. If the crack occurs after bisque-Hamer says it was probably unnoticed in the greenware. If the crack occurs after the glaze, it is because of glaze fit, or too thin of a base where compression of glaze and clay comes into play.

 

If this is the case, I highly recommend that you refrain from using a sponge in the later stages of throwing. The sponge just puts too much water into the clay. At the same time slow your drying time of the pieces before you trim them. You have said that you use a rib to compress, but are you compressing or are you scraping the wall shape. Two different things. A rib laid at an angle on the clay will push the particles together, where as a rib held perpendicular will not.

 

 

Thank you so much everyone for the information!!!...I am guilty of several "wrongs" you listed. You have all been so helpful. Deb

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when you go to trim, put a thumb tack in the inside bottom of your bowl. Then flip over, center and start trimming. When you hit the point of the thumb tack, you'll know how thick the bottom is. I think the stem of a thumb tack is too thick, but it is a start for getting yourself familiar with the feel of the thickness of your work.

Marcia

 

 

When I started throwing, I was always trimming too thin or through the bottom completely. I had some straight pins with the little colored balls on the head and cut them off at the thickness I wanted to trim to. Then, as you said, pushed a couple of them through from the inside of the pot, then began trimming. When I hit the tip, I knew I had gone far enough. The little balls made it easy to remove the pin, left no mark, and the hole was small enough that it healed up nicely.

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when you go to trim, put a thumb tack in the inside bottom of your bowl. Then flip over, center and start trimming. When you hit the point of the thumb tack, you'll know how thick the bottom is. I think the stem of a thumb tack is too thick, but it is a start for getting yourself familiar with the feel of the thickness of your work.

Marcia

 

 

When I started throwing, I was always trimming too thin or through the bottom completely. I had some straight pins with the little colored balls on the head and cut them off at the thickness I wanted to trim to. Then, as you said, pushed a couple of them through from the inside of the pot, then began trimming. When I hit the tip, I knew I had gone far enough. The little balls made it easy to remove the pin, left no mark, and the hole was small enough that it healed up nicely.

 

 

 

 

That suggestion is printed somewhere. They actually use regular thumbtacks in the bottom of the pot, so that you hit the pin as trimming. I taught beginning students how to do it, and then weened them off of it by having them check the thickness with their fingers after trimming each time-eyes closed. It was a good transitional tool.

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