Application of fingermark enhancement techniques on Clydesdale Bank and Royal Bank of Scotland £10 and £5 polymer banknotes in a pseudo-operational trial

Abstract

The aim of this study was to apply the two most effective enhancement sequences for latent fingermarks on Clydesdale Bank and Royal Bank of Scotland polymer banknotes (£10 and £5), as determined in a previous study, to a pseudo-operational trial. The two enhancement sequences established as being the most effective for these types of notes were superglue fuming using PolycyanoUV followed by black magnetic powder, and black powder suspension. Both enhancement sequences included a fluorescence examination before enhancement, and after-treatment using white light, followed by Infrared light. The study conducted by Joannidis et al. was carried out in a controlled laboratory environment where all variables, i.e., the position and age of each fingermark, were known and controlled. However, these conditions do not accurately mirror those of polymer notes seized as part of a criminal investigation. The two most effective enhancement sequences were therefore tested in a pseudo-operational trial to determine whether they would be as effective when applied to banknotes that mimicked those seized in an investigation. To mimic these conditions 102 banknotes from each bank (each containing a mixture of circulated and uncirculated banknotes) were left out in the laboratory for four weeks for the laboratory staff to randomly handle. The results from this pseudo operational trial confirmed the outcomes of the previous study. Superglue fuming (using PolyCyano UV) followed by black magnetic powder was found to be effective in enhancing fingermarks on both Clydesdale Bank and Royal Bank of Scotland polymer banknotes (£10 and £5). This was closely followed in effectiveness by powder suspension which, although it gave slightly poorer results than superglue followed by black magnetic powder, was also effective at enhancing ridge detail. This study also confirmed that Infrared light (730–800 nm), with the addition of an 815 nm filter for notes processed using superglue and black magnetic powder,aided in the reduction of background pattern interference when photographing any ridge detail.