Textile Fiber Analysis
Contributed by Eileen Davis
In a forensic context, when referring to this class of evidence one often speaks of the examination of fabric and cordage (e.g. rope, string, twine) as well as the individual fibers that make up these items. Because textile materials are so prevalent, textile fibers (referred to here as fibers), are a class of physical evidence that may transfer when two persons or a person and an object or location come into contact. If fibers are recovered from items of evidence, they are examined to determine if a possible association exists between individuals, locations or objects.
If fabric or cordage is involved, an examination will first be conducted to determine if a physical association (also referred to as physical match or physical fit) of a questioned item with a potential source exists. A physical association is the strongest conclusion possible when referring to fabric or cordage. If no physical association is possible then a comparison of the fibers composing the fabric or cordage will be conducted as well as an examination of the construction of the items. Likewise, if individual questioned fibers are recovered and a potential source is available, then a comparison of these fibers to possible source items will be conducted.
Fibers are typically mounted on glass microscope slides and examined using a comparison microscope. A comparison microscope consists of two compound microscopes joined together by an optical bridge and a single viewing head which presents a side-by-side view of the questioned and known fibers. Additional microscopic techniques include polarized light microscopy (PLM) and fluorescence microscopy. Instrumental techniques that also employ a microscope for viewing the fibers include, but are not limited to, Microspectrophotometry (MSP) and Fourier Transform Infrared Spectroscopy (FTIR). If at the end of all of the examination steps, the known and questioned fibers exhibit no observable differences, then they cannot be eliminated as originating from the same source. Due to the large production numbers of manufactured textile materials, the comparison of fibers is not a means of positive identification of individual fibers to a specific source. However, this examination may still provide meaningful information regarding the transfer of fibers.
1. Forensic Fiber Examination Guidelines, Scientific Working Group for Materials Analysis (SWGMAT)
2. Palenik S. Microscopical examination of fibres. In: Robertson J, Grieve MC, editors. Forensic Examination of Fibres, 2nd edition. London: Francis and Taylor, 1999.
3.Eyring, M. and Gaudette B. An Introduction to the Forensic Aspects of Textile Fiber Examination. In: Saferstein R, editor. Forensic Science Handbook, Vol. 2. Pearson Education, Upper Saddle River, NJ, 2005.