Applied Research in the Characterization, Identification, and Comparison of Pigmented Fiber Evidence

Fibers are one of the most common types of trace evidence encountered, and color is a primary feature of nearly every fiber comparison. Color is utilized at nearly every stage of analysis: from the initial search for target fibers and initial microscopical comparison of questioned and known samples, to late-stage objective comparisons by microspectrophotometry. In contrast to dyed fibers, pigmented fibers (i.e., solution dyed fibers) are colored by the addition of insoluble pigment to the liquid polymer prior to extrusion. The number of pigment types, their identity, particle size, and density of pigmentation represent unexploited properties that can be used to strengthen an association or provide investigative information during a fiber analysis. However, there have been no systematic studies of pigmented fibers; and therefore, no practical guidance is available to the bench-level analyst for the detailed analysis of pigments in forensic fiber cases. This applied research project will fill this knowledge gap through a systematic study of pigmented fibers. Starting with an assessment of industry trends in pigmented fiber production, the samples selected for study will span major manufacturers, major applications of pigmented fibers, and represent the variety of colors and polymers that are produced. These fiber samples will be characterized by analytical methods already available in many trace evidence laboratories: polarized light microscopy, Raman microspectroscopy, microspectrophotometry (MSP), and scanning electron microscopy/energy dispersive x-ray analysis (SEM-EDS). While advanced microanalytical methods will be used to establish the foundational aspects of this research, emphasis will be placed on the development of sample preparation, analysis, and interpretation approaches that are immediately accessible and applicable to casework analysts. Outcomes from this research will include a formalized approach to the identification of pigmented fibers by PLM, the practical identification of pigments in fibers by Raman microspectroscopy, the development of MSP-based pigment interpretation, and the use of electron imaging and elemental analysis to characterize pigment size, morphology, and distribution. The raw data will be compiled in a freely available database and the findings will be compiled in a peer-reviewed publication that provides practical guidance in the analysis of pigmented fibers and context by which the evidentiary significance of pigmented fiber evidence can be assessed. This research will provide a systematic foundation upon which this important type of fiber evidence can be transferred to federal, state, and local crime laboratories across the United States and around the world. NCA/NCF