When porcelains mature in the kiln they progress toward vitrification, getting softer. This simple test enables anyone to quantify the degree to which a porcelain is likely to warp. Bars of plastic clay almost never dry straight, so the measurement (in mm) to which they deviate from straight is recorded and the bar is mounted with the hump upwards. After firing the mm of firing deviation-from-straight are added to the dry value to derive a total pyro-plastic deformation measurement. This can be recorded as an absolute value for comparison with other clays or temperatures.
Pages that reference this post in the Digitalfire Reference Database:
This post is one of thousands found in the Digitalfire Reference Database. Most are part of a timeline maintained by Tony Hansen. You can search that timeline on the home page of digitalfire.com.