An Introduction to the Forensic Analysis of Solution Dyed Fibers

This week (18-22 March, 2023) scientists from around the world will gather in Philadephia for Pittcon 2023 Conference and Expo. On Sunday, March 19th, Microtrace Senior Research Microscopist Christopher Palenik will present a paper entitled “An Introduction to the Forensic Analysis of Solution Dyed Fibers” at the National Institute of Justice’s Advancements in the Analysis of Forensic Trace Evidence session of the conference. The paper was co-written by five members of Microtrace’s staff.

Microtrace’s work on this subject has been supported by a grant from the National Institute of Justice.

Abstract

“An Introduction to the Forensic Analysis of Solution Dyed Fibers”

Christopher S. Palenik*, Kelly Brinsko Beckert, Otyllia Abraham, Ethan Groves, Skip Palenik
Microtrace, LLC. *presenting author

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.

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