A DFAC drying test disk of a terra cotta pottery clay from St. Ignacio, Sinaloa, Mexico
Wednesday 19th October 2011
This clay is used by traditional potters in the Mazatlan, Sinaloa, Mexico area. This DFAC test shows a very wide main crack and many edge cracks. These combine to indicate high shrinkage (a product of very high insight-live.com/glossary/143">plasticity). Although the clay has some coarser grains that help channel water out, this is a very poor showing for drying performance, no large-scale manufacturer could tolerate this. That being said the Mexican potters use it with success! How? By adapting their drying procedures. The high dry strength of this material is also a factor to help prevent cracking. Almost any clay can be dried if it is done evenly. And any can be cracked if done unevenly enough. This DFAC test is also a good indicator of the amount of soluble salts present, in this case almost none.
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