This paper describes the development of microscopical methods for analyzing low explosive and other residues.
This study focuses on improving the direct visual comparison, microscopical identification, and chemical analysis of chemically reacted, i.e., unburned, partially burned, and fully burned materials, together with their resultant residues. This research also increases the overall understanding of the processes and mechanisms making it possible to obtain analytical results from physical evidence, particularly regarding the analysis of low explosive (LE) by a combined visual, microscopical, and microchemical methodology. The results of this research are multiple products that will aid forensic scientists in their analysis of LE and related evidence. The culmination of this research will include the specific methodologies being used, guidance on sampling for microscopical analysis, sample preparation techniques (including permanent slides), tables summarizing all known and verified optical characteristics, practical references, and numerous photomicrographs specifically arranged under a wide range of easily reproduced illumination conditions serving as an atlas of visual, photographic, and photomicrographic images. Data are compiled and presented with the aim of providing a practical and graphical methodology for the examination of these residues. The study includes a test method and analytical scheme, which can serve as a flow of analysis or guide in how to properly prepare, analyze, characterize, and compare a wide variety of particle types that may lead the microscopist to a positive identification. An LE characterization table containing all of the known and verified optical properties and additional information about each of the different types of particles including the most important oxidizers, fuels, metals, metallic salts, etc., is also provided. This is all accompanied by a photomicrographic presentation of various particles, with multiple photomicrographs arranged in singular pictorial composition and hundreds of images documenting the microscopical appearance of unburned, partially burned, and fully burned particle conditions.