Shrink Rule

Pottery tip of the day:

Shrink rule.

Take a metal ruler (I say metal because it does not warp or absorb water like plastic or wood does) then take a slab of the clay you would like to figure out the shrinkage of.
To determine the clay body’s shrinkage, roll out a coil of the clay to about six inches. Trim the coil to exactly five inches, cutting off both ends to make them flat and perpendicular to the table. Dry the coil, then fire it to the clay’s maturation temperature.

Re-measure the coil once it has come out of the kiln; be sure to use a ruler that measures in decimal fractions of an inch. Subtract the coil’s new length from the original five inches. Divide the difference by five (the original length). The answer is the shrinkage rate.

For example, let’s say the coil measures four and a half inches after firing. The difference is 0.5. Dividing by 5, we get 0.10, or a shrinkage rate of 10%.

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