An Assessment of the Value of Blue, Red, and Black Cotton Fibers as Target Fibers in Forensic Science Investigations

Color is the primary characteristic used for comparing cotton fibers. Problems arising because of considerable intrasample variation may cause difficulty in assessing the matching of cotton fibers in a casework situation. Because of the number of dye classes used on cotton fibers, dye extraction and examination by thin-layer chromatography are more problematical than with other fiber types. This necessitates greater reliance on microspectrophotometry and fluorescence microscopy for dye comparison. Fibers from blue denim cannot generally be discriminated and are regarded as having little evidential value. Little or no published data exist on the evidential value of cotton fibers of other colors. This study was designed to assess the value of nondenim blue, red, and black cotton fibers as evidence. Of each color 46 samples were chosen at random (giving a total of 1035 comparisons per color). The number of matching pairs was established after using comparison microscopy, microspectrophotometry, and fluorescence microscopy. Some blue denim cotton fibers were also examined. Complementary chromaticity coordinates were computed for all samples. The results show that, provided adequate techniques are used to compare nondenim blue, red, and black cotton fibers, the chance of finding pairs with matching dyes by coincidence is low despite considerable color overlap. Black cotton fibers represent poorer value as evidence than either nondenim blue or red cotton fibers.