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DiamondCore® Tools offers the unique Shrink Ruler, a flexible, two-sided plastic measuring tool designed for potters to gauge clay shrinkage with four clay shrinkage percentages, making it indispensable for precise projects like teapot lids and cookie jars.

The photos show both sides of the same ruler. One side shows 6% and 10%, the other side shows 12% and 14%.

HOW TO USE THE SHRINK RULER

Using your Shrink Ruler is easy! Here’s a step-by-step guide example:

1. Measure the dimension of the finished piece you want using a standard-inch ruler.
2. Find that measurement on the Shrink Ruler on the scale corresponding to the shrinkage of your clay.
3. Mark or form the wet clay piece to that dimension.
4. When the piece is done firing, it will have shrunk to the correct size.

HOW TO MEASURE THE SHRINKAGE RATE OF YOUR CLAY

To use the Shrink Ruler, knowing the shrinkage rate of your clay is important. Generally, the clay supplier can provide this, or you can calculate it using the formula below.

1. Make a rectangular clay slab that’s 4” (101.6 mm) X 12” (304.8 mm) and as thick as you plan to make your piece.
2. With a regular ruler, measure and carve a 10” (254 mm) line in the wet clay.
3. Let the clay dry, then bisque fire the clay slab.
4. Fire the slab to final firing conditions.
5. Measure the length of the same line again with the regular ruler.
6. Use the below formula to solve for S. 

S=(1-F/M)x100

M=length of line in original moist clay slab with a regular ruler (10”)

F= length of a line in a finished clay slab (with a regular ruler)

S=percentage of shrinkage