Brass cartridge cases are the most common type of cartridge case found at crime scenes, but it is not always feasible to obtain identifiable fingermarks on these cartridges. This study evaluates the effectiveness of gun blue as an enhancement method on fingermarks that were deposited on brass metal discs and left to age (2, 7, 14, and 30 days) under different environmental conditions, namely, under dark conditions, under ambient light, and outdoors. Ten different donors (5 males, 5 females) were employed for this study, and their fingermarks (60 per donor) were enhanced with gun blue solution (50% v/v). It was possible to enhance aged fingermarks (natural and groomed) that had been deposited on the brass metal discs to an identifiable level, with the fingermarks left outdoors being the most challenging to enhance. The feasibility of enhancing fingermarks on fired brass cartridges shot from different firearms was also assessed. Despite favorable results being achieved on fired brass cartridge cases, more research is required to assess whether reliable enhancement can be achieved on fired cartridge cases under real crime scene conditions
