•The secret to cool bodies and glazes is a lot of testing.
•The secret to know what to test is material and chemistry knowledge.
•The secret to learning from testing is documentation.
•The place to test, do the chemistry and document is an account at https://insight-live.com
•The place to get the knowledge is https://digitalfire.com

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Firing Clay Test Bars

Section: Clay Bodies, Subsection: Testing


Being able to make good consistent test bars and fire them in a consistent and proper way is a basic requirement of getting valid results for shrinkage and porosity measurement.

Article Text

An account at Insight-live.com is an online place to record data from your testing program. It defines many tests that can provide valuable information about the physical properties of clays, yet require little expensive test equipment to perform. You will probably agree knowing the chemistry of a clay material means little when compared to understanding its physical properties.

Insight-live test definitions are text-only and explain in detail exactly how to perform the procedures. We have tried to make-do with straight text where possible so that information can be sent via email and posted on our BBS and the Internet in a form easily used by anyone on any computer. While it is possible to describe most procedures adequately via text, I will show you two photos here that will help clarify two things in the procedure for the SHAB test (shrinkage and absorption properties) for making clay test bars.

The procedure given for stacking the bars is illustrated here. This angular stacked pattern encourages even heating of all bars compared to laying them on the kiln shelf, which acts as a heat-sink.

Notice that the three bottom bars are sawed from an insulating fire brick. The bars are piled at an angle to each other so that shrinkage has less likelihood of collapsing the stack.

Stamp used for stamping information onto clay test bars

Stamp used for stamping information onto clay test bars

This type of stamp is deal for stamping mix and ID information on SHAB (and many other test types) clay test bars. Set up the run or recipe number on the left and the specimen number on the right.

Example of test bars stacked into an electric kiln for firing

Example of test bars stacked into an electric kiln for firing

These have already been measured to deduce drying shrinkage. After firing they will be measured again to calculate the firing shrinkage. Then they will be weighed, boiled in water and weighed again to determine the water absorption. Fired shrinkage and absorption are good indicators of body maturity.

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By Tony Hansen

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