Optical Enhancement of Fingerprint Deposits on Brass Using Digital Color Mapping

Abstract

The reflection of visible light from α-phase brass subject to surface oxidation in air at elevated temperatures is investigated. X-ray photoelectron and auger electron spectroscopy confirm that covered areas of brass (not exposed to air) display dezincification but an absence of significant surface oxidation, confirming a differential oxidation mechanism. Visualization of differential oxidation is shown to be enhanced by selective digital mapping of colors reflected from the surface of the brass using Adobe ® Photoshop ®. Enhancement is optimal when the brass is heated to ∼250°C with areas of oxidation having a mirror-like appearance. The use of this enhancement method to produce a faithful image of fingerprint ridge characteristics is demonstrated on brass shell casings where fingerprints were deposited prefiring. © 2011 American Academy of Forensic Sciences.