High Resolution Imaging of Latent Fingerprints by Localized Corrosion on Brass Surfaces

Abstract

The Atomic Force Microscope (AFM) is capable of imaging fingerprint ridges on polished brass substrates at an unprecedented level of detail. While exposure to elevated humidity at ambient or slightly raised temperatures does not change the image appreciably, subsequent brief heating in a flame results in complete loss of the sweat deposit and the appearance of pits and trenches. Localized elemental analysis (using EDAX, coupled with SEM imaging) shows the presence of the constituents of salt in the initial deposits. Together with water and atmospheric oxygen--and with thermal enhancement--these are capable of driving a surface corrosion process. This process is sufficiently localized that it has the potential to generate a durable negative topographical image of the fingerprint. AFM examination of surface regions between ridges revealed small deposits (probably microscopic "spatter" of sweat components or transferred particulates) that may ultimately limit the level of ridge detail analysis.

Polymerisation of S2N2 to (SN)x as a tool for the rapid imaging of fingerprints removed from metal surfaces

“…Accordingly, and in light of topical forensic concerns, the study of S 2 N 2 interaction with cleaned fingermarks on metal surfaces, became paramount. 5 In contrast to standard chemical fingerprint detection techniques, the key feature of the results presented here is that even when the print is no longer chemically present, interaction with S 2 N 2 persists via the print's corrosive modification of the surface; crucially, this occurs even when 10 the print has had a relatively short time to manifest the corrosion. Figure 1 shows this effect in practice ‡ on brass plates.…”

“…Pioneering 35 work by Bond 10 and Williams 11 has revealed that instrumental techniques such as Atomic Force Microscopy and Scanning Kelvin Probe can image the minuscule surface corrosion effect generated by prints which have been laid down on metallic surfaces, even after the prints themselves have been 40 removed through various rigorous cleaning regimes. These results highlight the immense potential of such minor corrosive action on forensically pertinent substrates; however, the imaging techniques themselves suffer realistic limitations, such as the length of time required to process a macroscopic 45 area, cost and problems analysing irregular surface forms.…”

“…1 and and 2, the brass was 0.3 mm thickness CZ108 alloy and the stainless steel 0.5 mm thickness 316 grade. After exposure, brass samples were imaged 10 without any further treatment; steel samples were gently rinsed in CH2Cl2 to remove residual S4N4 which can sometimes deposit on the steel's oxide layer. The images in Fig.…”

Non-invasive, optical latent fingerprint acquisition from cartridge casings: A first feasibility study using a laser-scanning confocal microscope

“…The main advantages of this method are simplicity and low costs for instrumentation and reagents. Several approaches based on corrosion have been presented by Bond et al [3,4,5,6,7,8]. In [4] the authors evaluated the corrosion characteristics of latent fingerprints using ten metal elements and ten metal alloys.…”

Deterring gun crime materially using forensic coatings

“…Bottom-up nanotechnology has been useful in imaging latent fingerprint corrosion on fired brass [14] shell casings [15] that is enhanced by the presence of aqueous electrolytes [16] (e.g. Cl À in eccrine sweat), i.e.…”