Imaging fingerprint corrosion of fired brass shell casings

A newly developed method is presented for imaging fingerprint sweat corrosion of fired brass shell casings that reduces the degradation of the corroded fingerprint image. Degradation has been reduced by calculating a maximum angle of contact between the shell casing and a planar surface containing the imaging medium (graphite particles). Experiments have confirmed the predicted reduction in image degradation for contact angles less than the maximum. Details of the setup and operation of an instrument designed to improve fingerprint image quality are given and results shown for a 9 mm brass shell casing. Use of the instrument with other calibre ammunition is explained.