Digitalfire Test Procedure Database

Pyroplastic Deformation - PPD

Notes

A clays 'hot plastic strength', resists the tendency to deform in the kiln. The property is measured by making a thin clay bar, and firing this bar by supporting it at both ends only. Its deformation from straight is observed and recorded.

A clays tendency to warp is obviously related to its degree of maturity, however, the connection is not always what one may expect. Often a clay can be very volatile in this area. Sometimes there exist temperatures at which a clay body shows good resistance to warp during burning, however at slightly higher temperatures a greater than expected tendency to warp can be noted, even though fired shrinkage and absorption curves appear to show stability. Some potters expect linear stability from a clay body, no matter how overhung the bowl, how thin the vase, flared the goblet foot, or varied the firing, but a realistic appraisal of this property will reveal that much more attention needs to be paid to the cross section of pottery ware. Mature industrial ware is made from clay bodies which would warp badly in many a potters hands.

Make these bars the same size as those used in the SHAB test, but half as thick.

Variables

TEMP - Temperature (V)

Enter cone or temperature value.

WARP - Warp in mm (V)

Enter deformation from straight line.

Out Bound Links

• (Tests) SHAB - Shrinkage/Absorption
• (Typecodes) 5: BDT - Body Tests