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 exhibits a very wide main crack and many edge cracks. These combine to indicate high shrinkage (a product of very high 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. But potters can and the Mexican craftsmen use it with success! How? By adapting their drying procedures. The high dry strength of this material is also a factor that helps prevent cracking. Almost any clay can be dried if the process is done evenly. And almost any can be cracked if done unevenly enough. This DFAC test is also a good indicator of the amount of insight-live.com/glossary/254">soluble salts present (the slightly darker band around the perimeter), this is minimal so not scumming should appear on fired products.
Pages that reference this post in the Digitalfire Reference Library:
This post is one of thousands found in the Digitalfire Reference Database. Most are part of a timeline maintained by Tony Hansen. You can search that timeline on the home page of digitalfire.com.