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Comparison of glass particles by the forensic scientist is routinely accomplished by measuring some physical properties. Direct comparison of densities ϱ and refractive indexes (ͻC, ͻD, and ͻF being the refractive indexes determined at 6563, 5893, and 4861 nm, respectively) are the most widely used physical measurements because of convenience, reproducibility, sensitivity, and applicability to small sample size. Traditionally, if the physical comparison showed significant difference, it was concluded that the two glass samples could not have had a common origin. Conversely, when the specimens were not distinguishable the forensic scientist reported these samples as possibly having the same origin. Generally he did this without giving consideration to another variable-elemental composition of the samples.

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By statistical analysis of probabilities, the value of density, refractive index, and dispersion for identifying the source of glass samples is evaluated. Empirical tests validated the statistical conclusions. It was determined that density has by far the greatest differentiating power of the three parameters tested; assuming equal thresholds of discrimination, density has a differentiating power some six times greater than that of refractive index. Dispersion offers little, if any, improvement over refractive index. Density and refractive index together are somewhat greater in value than density alone.