Effect of water immersion on multi- and mono-metallic VMD

Abstract

The use of vacuum metal deposition (VMD) for fingermark detection has been known for almost 40 years. The technique is applicable on a wide variety of substrates and on wetted items. Several publications compare the relative efficiency of VMD (conventionally based on a successive vaporization of gold followed by zinc) with other detection techniques, or its ability to detect marks on difficult substrates, but few are known about the application of monometallic VMDs and about the impact of immersion on the detection performances. This study aims at partially filling that gap by offering a quantitative and qualitative glance at three VMD processes (i.e., gold/zinc, silver, and sterling silver) applied to dry and wetted substrates. The impact of immersion on the detection process has been studied by using split marks (one half kept dry, the other one wetted). On immersed substrates, a modification of colour shades has been observed with monometallic VMDs (on all substrates considered) and of contrast with conventional VMD (on polyethylene). In terms of ridge details, a relatively good resistance of secretion residue towards immersion has been emphasized (in regards with VMD). This study provides original data, which will hopefully help getting a better understanding of the VMD detection mechanism.

A Preliminary Study on Vacuum Metal Deposition as a Standalone Method for Enhancement of Fingermarks on Ballistic Brass Materials

“…The disks (3 9 3 cm) had been previously cleaned with 5% v/v Decon 90 solution, followed by ethanol and left to air dry. Each donor deposited 12 full fingermarks (which is an adequate number for a preliminary study [17]) which were divided into four even groups according to the number of days they were left to age before development (2,7,14,35 days old), the aforementioned time ranges were chosen based on fingermark research and guidelines in the literature (16,17). The disks were stored under dark and dry conditions, with temperatures ranging from 15-20°C and were only accessible to the authors.…”

“…One of the greatest advantages of VMD includes its versatility, including its suitability for a wide range of substrates, including wetted ones . VMD is also ideal to use as a sequential treatment, as it does not damage any DNA that may be present in fingermarks (since it targets the metallic substrate and not the fingermark itself), and works well with other conventional fingermark enhancement techniques such as cyanoacrylate fuming .…”

“…The use of VMD as a tool for the forensic enhancement of latent fingermarks was first proposed in 1968 ; however, a substantial number of years passed before it would be considered as a viable enhancement technique. VMD was initially introduced in the forensic field to detect fingermarks on paper and was then optimized to be fully operational in the late 1970s. The method involves placing the item to be treated inside the deposition chamber which is sealed/operated at a high vacuum, typically larger than 3 × 10 −4 mbar.…”

Vacuum metal deposition enhancement of friction ridge detail on ballistic materials

“…[24] and has shown success on several notoriously difficult substrates such as polymer banknotes and fabrics [25,26]. Unlike CA fuming, VMD can also be used on exhibits that have previously been wet [27], and is recommended for aged marks [6].…”

Blast Suppression Foam, Aqueous Gel Blocks, and their Effect on Subsequent Analysis of Forensic Evidence*

“…Alternatives include physical developer, Oil Red O, and phase-transfer catalysts (65)(66)(67). Sebaceous prints on nonporous materials that have been wetted may be developed with particle suspension reagents, powder, superglue, or vacuum metal deposition, albeit with diminishing success as immersion time increases (56,57,(63)(64)(65)(68)(69)(70)(71)(72)(73)(74)(75). Of particular relevance to the present study, immersion in soapy water decreases development success (31,52,56,76).…”