April 02, 2011

Clay Ruler

Shrinkage Test

All clay shrinks, physically and chemically, through water loss and vitrification. From leather hard to bone dry through bisque and finally to full maturity ceramic objects change and reduce in scale. We always plan for this in our designs. I, however, always get used to working with my plaster models and unfired cast items that when i eventually get to a fully glazed item, it's always so small!
Here's a little run down of my test for PSH's 811 Porcelain slip.

Original slab starting at 150mm

Bone Dry 144mm

Bisque (cone04) 141mm

Maturity (cone 6) 133 mm

This little ruler allows me to design my forms well, I know the shrinkage is about 12.7%  If I need a 20 cm tumbler, i know my form needs to be about 22.5 cm to begin with.

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