Metal Deposition Chemistry for the Visualisation of Latent Fingermarks

Due to their unique nature, fingermarks are the prime means of identification of an individual. Operationally, the most useful marks are latent (non-visible) fingermarks, typically left by accidental contact, which must be visualised by chemical development techniques. There is a continuing need for simple, rapid, sensitive development techniques, involving safe reagents and ideally usable at a crime scene. This thesis addresses that challenge by galvanic deposition of one metal onto a less noble metal, using the fingermark residue as a barrier to the deposition process. Although successful at visualising fingermark, this technique is in a developmental stage and is not yet fully validated for standard use by practitioners. The primary focus was optimisation of galvanic deposition of copper to enhance marks on mild steel (iron containing) substrates, representative of knives, tools and other objects of forensic relevance. The quartz crystal microbalance (QCM) technique was used for gravimetric characterisation of the deposition/dissolution processes occurring during development. Of several reactions identified, galvanic copper deposition was dominant, accounting for 63% of the substrate mass change. The effects of temperature and alternative development solution delivery to the surface were explored. Based on highly successful latent fingermark development on iron by the copper reagent system, generalisation of the method to other substrates and metal ion reagent systems was explored. Thermodynamic considerations provided electrochemical criteria and revealed a number of candidate substrate/reagent combinations. Experimental measurements of the underpinning science were undertaken for two cases of potentially relevant forensic application, involving copper deposition on nickel and tin. After optimisation of immersion time and solution copper concentration, galvanic copper deposition on tin proved particularly successful for latent fingermark enhancement. The developed fingermarks were characterised and analysed using digital photography, image optimisation, scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) analysis.