ASTM C368-88(2016)

Note 1: The impact test at the center of the specimen is used to determine: (1) the magnitude of a blow that will produce initial fracture, and (2) the amount of energy necessary to produce complete failure. In the first case, the initial fracture shows on the side of the piece opposite from that being struck and appears to be a function of the square of the thickness and of the inherent brittleness of the body or body-glaze combination; it is relatively independent of the size or design of the specimen. The second factor is more dependent upon design and often is subject to wide variation within a given group of pieces.

Note 2: The impact test at the rim of hollow ware is similar to a chipping test, and the type of failure that is obtained is useful in evaluating the effect of the shape of the object.

Note 3: In addition to the inherent strength of the body, chipping test results are greatly affected by contour of rim and to a lesser extent by thickness of rim, inclination of leaf, and fit of glaze.