Comparison of Vacuum Metal Deposition and Gun Bluing for Developing Latent Fingerprints on Fired Nickel-Plate Brass Ammunition
Abstract
Vacuum metal deposition (VMD) is a highly sensitive method for developing latent fingerprints on semiporous and nonporous surfaces with extensive research focusing on various classes of polymers. The relatively high cost of a VMD unit and the need for an experienced operator, has prevented the technique from replacing traditional methods, such as gun bluing, for developing latent fingerprints on spent cartridge casings. A literature review revealed that while VMD has the potential to be a powerful technique in the development of expended cartridge casings, there is a lack of comparison studies between VMD and other latent print development techniques on shell casings. The purpose of this study was to determine if there is a significant difference in the equality of latent fingerprints developed by vacuum metal deposition and gun bluing (GB) on fired cartridge casings. To accomplish this, a single latent print spiked using a sebaceous oil reference pad was deposited on 250 9mm nickel-plated brass ammunition samples and developed by either VMD or GB. From these 250 casings, 50 were treated in a brief preliminary study that subsequently guided the gun bluing process. As a result, a modified gun bluing protocol using a 20% Brass Black (Birchwood Casey, Texas, USA) solution was followed to process 100 casings while the remaining 100 were subjected to silver/zinc deposition in the VMD560 (West Technology Forensics, England, UK). All casings were photographed, examined, and graded on a 0-4 scale by a Certified Latent Print Examiner. Of the 200 casings developed, 115 samples failed to yield any ridge details (Grade 0) with 54.78% having been developed by VMD. There was limited ridge detail (Grade 1) present on 62 samples with comparable results from both techniques. Low quality detail (Grade 2) was visualized in 23 samples with 86.96% having been produced by GB. Using the Kruskal-Wallis H test with a 90% confidence level to determine statistical significance, the primary hypothesis that VMD would be the superior method was not supported. Therefore, it is recommended that nickel-plated brass casings be processed using the modified GB protocol.
Description
Keywords
Fingerprints, Latent fingerprints, Vacuum metal deposition, Firearms
Citation
Osborne, A. (2020). Comparison of Vacuum Metal Deposition and Gun Bluing for Developing Latent Fingerprints on Fired Nickel-Plate Brass Ammunition.