>>>Could anyone tell me why my students wheel thrown pots will get cracks
>>> in the bottom of their ware?
Maybe this will help although I am not a clay guru.
I have my students build a tall cone and then push it down with their palm
to resemble a tuna fish can, all the while keeping one supporting hand on the
side. We do this about three times to "strengthen" the clay and realign the
clay particles. Then we continue to build and shape the pot. We also use a
sponge on a stick to sop up water laying inside the base.
Many times when students throw a pot, the circumference around the base is
much thicker than the resulting sides and bottom. I have the students work
with a wood trimming tool to remove some of the clay thickness from the
"base-sides".. This enables evener drying and eliminates "wobbles" on the surface.
Another thing we do is place a dampened paper towel on the rim to slow the
drying at the top.
Do you allow time for the clay to really become bone dry? To be sure, we
candle for about 12 hours at low temp. with the lid up and plugs out. Our
objective is to allow any additional moisture in the clay to evaporate before
We have had the success with this method. When we get an occasional cracked
pot, we know the clay was not wedges well. We can actually find spaces
(bubbles) in the shattered pieces.