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

• Film growth and selective corrosion of the metal substrate have been studied.
• Heating, anodising, iodine, ammonium sulphide, peroxide and acid were investigated.
• Interactions of fingermark, metal and reagent were examined by SEM, EDX and confocal microscopy.
• It may be possible to recover fingermarks on metal after fires or immersion in water.

The interaction of fingermark deposits on metals has been examined by a variety of techniques. Visualisation by film growth has been the main area of investigation through: thermal oxidation, anodising, peroxide solution, and the interaction with vapour of iodine and ammonium sulphide. Corrosion of the underlying metal has also been examined as an alternative means of visualisation.Confocal microscopy was used to look at the film thickness and corrosion products around the prints. Scanning electron microscopy and energy dispersion of X-rays (SEM-EDX) examined a number of metal samples to investigate film growth and the elemental distribution. The observations suggest that differential oxidation was occurring as well as corrosion into the metal. Fingermark deposits on metals can corrode into the metal depending on the reactivity of the metal and leave a recoverable mark. However, fingermark deposits can also alter the rate of chemical reaction of the substrate metal by oxidation. In some cases organic matter can inhibit reaction, both when forming an oxide layer and when corroding the metal. However, signs of third level detail from pore contact may also be visible and the monovalent ions from salts could also influence film growth.Whilst further work would need to be carried out to decide whether any of these techniques may have application in fingermark recovery, this study does suggest that fingermarks on metals may be recoverable after incidents such as fires or immersion in water.