NCJ Number
218652
Date Published
January 2005
Length
5 pages
Annotation
The Scientific Working Group for Materials Analysis presents guidelines for determining the density of glass.
Abstract
The guidelines indicate that the density of an unknown sample of glass is determined by placing a glass sample into suspension in a liquid solution. The density of that liquid is then either measured directly or used comparatively with another sample of glass. In discussing the significance and use of glass density in an investigation, the guidelines note that glass density varies with changes in the glass's composition and thermal history. If two samples of glass have different densities, they are from different sources. Density may be used as an initial screening technique when a large number of fragments have come from a crime scene. Four guidelines pertain to sample handling. One guideline advises that samples must be clean and dry before proceeding to an analysis. Guidelines are provided for two methods of analyzing glass density: the density gradient column method (Kirk, 1951) and the sink/float method. The density gradient column method involves placing a liquid containing a gradient of density in a vertical glass tube. The gradient is such that the density at any level is less than that at any level lower in the tube and greater than that of any level higher in the tube. When glass fragments are introduced to the column, each will become suspended in the liquid at the level that is the same density as that glass fragment. The sink/float method involves suspending glass fragments in a density solution within a constant temperature bath. If two or more fragments are suspended, their densities are the same. The numeric density value is not determined in this method but can be determined by using the absolute density determination methods described in this report. 4 references