Evaluation of the solvent black 3 fingermark enhancement reagent: part 2 - investigation of the optimum formulation and application parameters.

A comparison is reported of the relative effectiveness to two formulations of the solvent black 3 (Sudan Black) reagent used to enhance grease contaminated fingermarks. These experiments compared the currently recommended ethanol-based formulation with a lower flammability system based on 1-methoxy-2-propanol (PGME) using natural, deliberately sebaceous and grease contaminated marks across a range of surfaces. It is shown that overall the PGME-based formulation was significantly better at producing good ridge detail on most surfaces for both natural and deliberately sebaceous prints, and for contaminated prints the ridge detail obtained with the PGME-based formulation was as good or better than that obtained with the ethanol formulation. Several smaller experiments were also carried out in order to provide additional information on the solvent black 3 process. These showed that solutions of age up to 2 years can still develop good ridge detail, but the colour of the stained mark may vary. It was also demonstrated that the currently recommended 2 minute treatment time often resulted in very heavy background staining and in practice significantly reduced treatment times can be recommended according to the nature of the surface present.