Pot Cracked And Became Soft In Water
Posted 29 May 2011 - 10:57 PM
I'm new to this forum and to pottery making so please forgive me for not knowing some of the basics or some of the terms.
I was testing the suitability of a new clay source I found out in the woods by making several small test pots. I dug up the clay, added varying amounts of Tuff (volcanic ash rock) temper and fired them in a pit (no kiln). They were not slipped or polished. Today I decided to test how waterproof the pots were so i filled one (this one was made with 40% temper) with water and left it sitting for about 10 minutes. Now I totally expected that the pot would be super porous and water would leak out big time, but what I didn't expect is that the pot cracked in multiple spots all starting at the rim and working their way down. Also when I tested the strength of the wall of the pot, a whole fragment/sherd broke off along a crack. The wall body had become soft, which I never would have expected since it was fired a couple of months ago.
Does anyone know why this pot cracked and the paste body had become soft? Was there too much or not enough temper? Is it the clay itself? Was it not fired hot enough?
Any suggestions would be appreciated.
Posted 30 May 2011 - 10:03 AM
Marcia Selsor, Professor Emerita,
Montana State University-Billings
Marcia Selsor Studio in Brownsville, Texas.
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