Expansion of Photographic and Microscopical Resources for the Identification of Low Explosive Residues

Polarized light microscopy, stereo microscopy, microchemical and spot tests were used to examine, analyze, and document materials commonly used in low explosives and often associated with improvised explosive devices. Examination, analysis, and documentation was carried out on readily available chemical oxidizers and fuel sources in three conditions; unreacted, partially burned and fully burned. Materials included in this study include oxidizers such as potassium nitrate, urea and urea nitrate as well as fuels such as woodmeal, sugar, starch, dextrin, sulfur, ground spices, red phosphorus, and aluminum powders. The optical properties were recorded in each condition and most importantly, an array of photomicrographs were taken using various microscopical techniques; plane polarized light, crossed polars, partially uncrossed polars, reflected light and fluorescence when applicable. Optical properties as well as morphological features which assist in the identification of materials used in this study are also documented. Additionally, several microcrystal and spot tests were evaluated and found to be applicable for the identification of materials in their intact and partially burned states, specifically tests for aluminum and urea. Photomicrographs will serve to expand the limited photographic resources currently available to the trace evidence examiner and the additional use of spot and microcrystal tests will also aid the examiner in the identification of materials in various conditions which may result after an explosion or blast has occurred.