Pottery and Ceramic Clay
Pottery Cracking and Wheel Throwing
Cracks develop on pottery for two main reasons:
Tools for Pottery
Tips & Techniques for Pottery and Ceramics
Clay Pottery Craft Projects
Clay Pottery Articles of Interest
Old Time Pottery History
Pottery and Ceramics
Featured Potters Gallery
Pottery and Ceramics Definitions
All About The Clay
All About Pottery Glazes
This problem can certainly be avoided by following a few simple tips
Cracks develop on pottery for two main reasons:
Uneven Drying
Do you put your wheel thrown work in a drying cupboard?How about covering your work with plastic sheeting, trying to ensure even drying?
Now, if you are throwing pottery on a bat, no air reaches the bottom of a platter, vessel or other thrown object, right?
So,what happens?
Well, I'll tell you what I have learned.
The top of the pottery dries a bit faster.
As the top dries, it shrinks and pulls together, cracking the wetter and less shrunk surface towards the bottom.
Once a crack has developed on pottery, it is almost impossible to get rid of, even by trimming.
One way to get around this, is to turn your pottery over halfway in between the drying process, but this usually can't be done.
This is how I got the bottom drying at the same rate.
Simply throw your pottery on plaster bats.
The bat will need to be moistened, otherwise the clay will pop off too soon and throwing will become impossible.
After throwing your pottery, the piece can be lifted off while still on the bat and the bat (work and all) can be placed in your normal drying area.
After a few hours, depending on moisture content of the bat, the work will pop off all by itself and your pottery may even be ready for turning and trimming that same day.
Uneven Compression When Wheel Throwing
This Cracking apeared after firing the second time.
Rougher clays like raku are generally not so prone to cracking, unless they are treated badly, as the grog tends to absorb a lot of tension.
For finer clays, the best way to get a evenly compressed clay throughout is to center the clay on the wheelhead, then cut off the clay with a cutting wire.
Turn the clay and recenter it upside down.
This makes sure that the clay will be compressed at the bottom as well as at the top, avoiding those dreaded S cracks!
Uneven Kiln Firing
Uneven firing can also cause pottery to crack.If one side of the pottery gets more heat than the other, it can shrink more rapidly, causing tension, which will lead to cracks developing as the pottery cools.
Combined, these techniques should help to cure most of your wheel thrown pottery cracking problems.
| No time is ever wasted that makes two people better friends. |
