Forensic discrimination of dyed hair color: I. UV-visible microspectrophotometry.

Current protocols for examining hair do not attempt to differentiate hair color using instrumental analysis. In this study, hair samples treated with 55 different red hair dyes were analyzed using UV-visible microspectrophotometry between 200 and 700 nm. Using air as a background reference gave the best results, although mounting media such as glycerin could also be used. The contribution of the hair substrate is predominantly observed in the range of 300-400 nm while the dye peak is evident in the range of 425-550 nm. It was found that the presence of hair dye reduces the overall intrasample variability of the hair color. In addition, visual inspection and spectral interpretation showed that dyed hair exhibits distinct and discernable shades. The color of all samples was stable during storage and while all hair dyes fade with washing, significant fading of the color was only evident after daily washing for 3 weeks.