On the electrical characteristics of latent finger mark corrosion of brass

Abstract

Apparatus constructed to measure the variation (ΔV) in applied potential (V) over the surface of brass discs subject to corrosion by latent finger mark deposits is described. Results show values of ΔV of up to 14 V for V = 1400 V on regions of disc coincident with the location of finger mark corrosion. Measurement of ΔV for 0 V ⩽ V ⩽ 1400 V has revealed a non-linear relationship, which is very similar to that measured for a commercial metal–semiconductor Schottky rectifier. Further experiments have shown the corrosion product on the brass to be a p-type semiconductor with current/voltage characteristics for the brass-corrosion contact consistent with the characteristics expected for a rectifying metal–semiconductor contact. The composition of the semiconductor is discussed in terms of metal oxide corrosion products with p-type copper (I) and copper (II) oxides thought most likely to be responsible for the semiconductor behaviour of the corrosion product. A simple model is described for the galvanic corrosion of brass by finger mark deposits that is consistent with the experimental results.

The thermal visualisation of latent fingermarks on metallic surfaces

“…Forensic science Latent fingerprints Latent fingermarks Metal Metallic surfaces Enhancement Visualisation A B S T R A C T Recent published research has lead to improved techniques for recovering latent fingermarks from metallic surfaces. The present study corroborates and extends some of the work carried out by Bond [1][2][3], but an alternative mechanism is proposed for the thermal visualisation of fingermarks based on differential oxidation and the production of interference colours that improve contrast. Fingermarks treated at low temperature could be reheated to enhance recovery, but an upper temperature limit occurs beyond which the mark degrades.…”

“…Fingermarks can be recovered by a range of traditional methods such as powdering and cyanoacrylate fuming but these sometimes have limitations and a range of alternative techniques for mark enhancement have been considered over the years. A significant development was made with the recent work published by Bond [1][2][3], and in these papers he reviews earlier research into fingermarks on metals.…”

Visualization of Latent Fingerprint Corrosion on a Discharged Brass Shell Casing

“…2, a series of small black dots can be seen both within the darkened area of conducting powder and also in the area immediately above it. It is thought that this may be indicative of black copper (II) oxide formed during the corrosion process and which has been observed previously (10). Interestingly, there has been no adherence of the conducting powder to the reference number engraved into the lower right hand side of item 3, which might be expected if the adherence of the conducting powder was determined by the occurrence of a depression in the metal surface rather than a change in its electrical properties (8,10).…”

The interaction of fingermark deposits on metal surfaces and potential ways for visualisation

“…Recent work by Williams et al [1,2] and Bond [3][4][5] has increased the interest in this area. Williams used a scanning Kelvin microprobe to measure the potential across a surface film on 100 mm spacing and interpolated data with a commercial software package.…”