Visualization of Latent Fingerprint Corrosion of Brass

Visualization of latent fingerprint deposits on metals by enhancing the fingerprint-induced corrosion is now an established technique. However, the corrosion mechanism itself is less well understood. Here, we describe the apparatus constructed to measure the spatial variation (Delta V) in applied potential (V) over the surface of brass disks corroded by latent fingerprint deposits. Measurement of Delta V for potential of 1400 V has enabled visualization of fingerprint ridges and characteristics in terms of this potential difference with Delta V typically of a few volts. This visualization is consistent with the formation of a Schottky barrier at the brass-corrosion product junction. Measurement of the work function of the corroded brass of up to 4.87 +/- 0.03 eV supports previous results that suggested that the corrosion product is composed of p-type copper oxides. A model for the galvanic corrosion of brass by ionic salts present in fingerprint deposits is proposed that is consistent with these experimental results.