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Specific Gravity
This is the weight per unit of volume of the slip. Specific gravity is defined as the comparison of a liquid's weight with the weight of an equal volume of water. In metric it is even simpler: water weighs one gram per cc (ccs and milliliters are the same). If a liquid weighs 1.8 grams per cc, then it has a specific gravity of 1.8; it is 1.8 times heavier than water. A slip with a specific gravity that is too high is said to be “heavy”. If the viscosity is too high, it is said to be “thick”.
The more water in a slip, the lower its specific gravity will be. The more solids, the higher it will be. As mentioned, slip with too much water will soak the molds more quickly, give slow casts, and result in excessive shrinkage that cracks the ware.
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Patricia Walters-Fischer |