An Introduction to the Forensic Analysis of Solution Dyed Fibers

Description:
A solution dyed fiber is colored by discrete, micrometer to sub-micrometer sized particles of insoluble pigment. This is in contrast to a dyed fiber, in which soluble dye molecules bind to reactive sites of the polymer comprising the fiber. Solution dyed fibers have been growing in market share due to their chemical and light stability coupled with a push towards environmentally friendlier manufacturing practices. The recognition of solution dyed fibers, the identity and characteristics of the pigments used to color them, and the number of pigments used to achieve a color represent unexploited properties directly relevant to a forensic fiber analysis.

Here we present a systematic study of solution dyed fibers, to provide practical guidance to the bench-level trace analyst, through a purely visual microscopical examination by polarized light, oil immersion, and fluorescence microscopy. A set of seventy five solution dyed fiber samples that spans major manufacturers, applications, colors, and polymers were selected from Microtrace’s curated collection of several thousand solution dyed fibers. Various preparation methods and mounting media were explored to optimize the direct visualization of these minute pigments, which approach or exceed the resolution limit of light microscopy. Through longitudinal and thin cross section preparations, discrete, colored pigment particles or agglomerates of these particles were recognized in all solution dyed fibers studied, thus presenting a reliable manner by which a solution dyed fiber of any size can be recognized in a forensic analysis. In each fiber sample studied, the number of different pigments and their color, fluorescence, morphology, contrast (relative refractive index), and pleochroism provide points of comparison obtained through a purely visual microscopical analysis. The overall dataset generated from this set of fibers provides new insights into the significance of solution dyed fiber evidence.

Speaker: Christopher S Palenik - Microtrace
Christopher Palenik grew up thinking that every home had a library and a laboratory. With visitors from forensic laboratories around the world routinely at his childhood dining room table, Chris became fascinated with the breath of practical information that can be revealed through thoughtful scientific analyses. With an educational background that spans chemistry, geology, materials science, and nuclear engineering, Chris has studied at forensic laboratories around the world, developing an intimate familiarity with a wide range of materials and microanalytical approaches. Chris is a microscopist at Microtrace, a private microanalytical problem solving laboratory outside of Chicago that provides scientific support for criminal, military, civil, and patent litigation; clients in pharmaceutical, food, and manufacturing industries, and buyers and sellers of fine art, antiquities, and collectables.