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These are the oversize particles (from the 70, 100, 140 and 200 mesh sieves) from 100 grams of a commercial ball clay. They have been fired to cone 10 reduction. As you can see, this material is a potential cause of specking, especially in porcelain bodies. It is not only wise to check for oversize particles in clays, but firing these particles will tell you if they contain iron. A 200 mesh screen would be a good start for this test, it would catch all of these.
Troubles |
Specking on Ceramic Ware
Specking, or speckling, can be both a fault or feature in fired ceramic ware - caused or produced by metal-bearing contaminants to metallic additives |
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Materials |
Ball Clay
A fine particled highly plastic secondary clay used mainly to impart plasticity to clay and porcelain bodies and to suspend glaze, slips and engobe slurries. |
Tests |
Sieve Analysis 35-325 Wet
A measure of particle size distribution by washing a powdered or slaked sample through a series of successively finer sieves |
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