Optical Enhancement of Fingerprint Deposits on Brass Using Digital Color Mapping

The reflection of visible light from alpha-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 (R) Photoshop (R). Enhancement is optimal when the brass is heated to similar to 250 degrees 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.