A Potter's Journey, Ceramics

Unfired Clay vs. Fired Clay

This picture shows the comparison of the same pot — unfired Cinco Rojo clay dipped in porcelain slip, and then glazed with a clear glaze and fired at cone 6 (which is 2269 degrees F). There is quite a difference in the color of the clay from unfired to fired–rich, deep red to a chocolate brown. The clear glaze actually seems to accentuate the speckling in the stoneware.

comparisonbowls

 

 

 

 

 

 

Next time I fire this clay, I think I will take it only up to cone 5 (which is 2205 degrees F — a difference of only 64 degrees.) BigCeramicStore.com has this very useful chart that shows the correlation of temperature to cone number, and also which type of clay “matures” at what temperature. According to this chart, firing this red clay that additional 64 degrees took it beyond its melting point, which could account for the change in color. Not that it isn’t lovely as a chocolate speckled stoneware. It’s just not what I wanted to see.

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