Determination of the most effective enhancement process for latent fingermarks on Clydesdale Bank and Royal Bank of Scotland £5 and £10 polymer banknotes

Fingermarks are commonly found at crime scenes and can be used to link an individual to an object and/or place. One common evidence type regularly encountered in the course of a criminal investigation is banknotes, and the recovery of fingermarks from these notes can give an indication of who has handled them. This study was carried out in order to determine the most effective sequential processing techniques for recovering latent fingermarks on the new £5 and £10 Clydesdale Bank and Royal Bank of Scotland polymer banknotes. No previous studies have been published on the recovery of latent fingermarks from these types of polymer notes; therefore, this work provides valuable insight into the challenges associated with these notes. Initial experimentation was done in order to determine the best light source to be used in combination with each sequential process tested. From this, infrared (730–800 nm) and ultraviolet (350–380 nm) light were chosen for use in the main study. Black iron oxide powder suspension and black magnetic powder were two of the enhancement treatments tested, both of which are recommended ‘Category A’ processes in the Fingermark Visualisation Manual produced by the Home Office. Superglue fuming – using PolyCyano UV—which is a Category C process was also used, as well as the recently developed infrared fluorescent powder, fpNATURAL®2. Three fingermark donors were selected for this study—one good, one medium and one poor—and each donor deposited a 10-mark depletion series onto both sides of each type of note. Superglue fuming (using PolyCyano UV) followed by black magnetic powder was found to be the most effective sequential process for enhancement of fingermarks on all note types tested. Infrared (730–800 nm) light with an 815 nm filter was the most effective light source for enhancing ridge detail for this enhancement sequence. This process is now being implemented for use with these note types in Scotland.