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.