2-15. BREAKAGE - GLASS CONTAINERS
Breakage of glass containers can be divided into three categories, which are
based on the cause of the break.
a. Internal Pressure. This break has a definite pattern (see Figure 2-10) and is
usually midway between the top and bottom of the jar.
b. Impact. The container is broken by active impact or by a series of small
impacts. There is radial forking. Percussion cones may be formed (see Figure 2-10).
Thin-walled containers resist impact breakage best. Those with thick walls are too rigid.
c. Thermal Shock. When two portions of a glass container are at widely
different temperatures, one expands and the other contracts. Mechanical stress and
strain causes a bottle to break from thermal shock (see Figure 2-10).
Figure 2-10. Breakage characteristics of glass jars.
2-16. SURFACE MARKINGS-BROKEN GLASS CONTAINERS
The surface of a broken glass container has characteristic markings from which
information about the break can be obtained (see Figure 2-11).
a. Origin of Break. Where the break occurred can be determined by tracing the
surface markings backwards.
b. Ripple Markings. These marks indicate an area of moderate violence in the
movement of the fissure.
c. Feathering. This indicates that the fissure forces have slowed.