|Even if you love the sculpture or pottery clay you use, at one point or another, the need or desire to change your clay body can arise. You might want a clay body that shrinks less, or want to change from an iron rich clay body to a porcelain. Whatever the reason, whether you are buying commercial clay or mixing your own, it is always a good idea to test clays before purchasing large quantities. Even though commercial clay bodies might have catalog descriptions that sound just right or another potter swears by a certain pottery clay recipe, once we apply our specific working and firing processes, results can vary. Today, Paul Wandless explains how a combination of simple tests can give you plenty of information that will make choosing and learning about pottery and sculpture clays a little easier. - Jennifer Harnetty, editor.|
Why Test Your Clay Body?
|What to Test your Clay Body For|
Tests should be done at multiple temperatures to yield the widest range of information on the clay body. You need to understand the same general characteristics at every temperature you fire to, and even at temperatures you may want to fire to in the future. I test at every potential cone I may fire to and keep records of all the results.The three important general characteristics to take note of are shrinkage, absorption and warping/slumping. Other important qualities to note are color, texture, plasticity and hardness. Some results are determined with visual and touch tests while others require simple formulas. All require consistency of procedure so the results you achieve are created under the same conditions.
Firing Box and Stilts
For the tests here, I've selected four bodies to test: two white bodies
Once all bars are cut and firing boxes are built, let them dry to bone
Before the Bisque
For each firing, place the bars side by side in the firing box, and
The weight calculation test is more specific. Weigh the fired bar on a
This post was excerpted from Electric Firing: Creative Techniques, which is available in the Ceramic Arts Daily Bookstore.