Vacuum Metal Deposition: Factors Affecting Normal and Reverse Development of Latent Fingerprints on Polyethylene Substrates

Elsevier Science Ireland Ltd
Publication Type:
Journal Article
Forensic Science International, 2001, 115 (1), pp. 73 - 88
Issue Date:
Full metadata record
Files in This Item:
Filename Description Size
Thumbnail2004004611.pdf1.22 MB
Adobe PDF
Vacuum metal deposition (VMD) is an established technique for the development of latent fingerprints on non-porous surfaces. VMD has advantages over cyanoacrylate fuming, especially in circumstances where prints are old, have been exposed to adverse environmental conditions, or are present on semi-porous surfaces. Under normal circumstances, VMD produces `negative prints as zinc deposits onto the background substrate and not the print ridges themselves. A phenomenon of `reverse development, when zinc deposits onto the print ridges and not the background, has been reported by many authors but its causes have not been conclusively identified. Four plastic substrates were used in this study and these could be easily divided into two groups based on the types of development observed as the amount of deposited gold was increased. On group I plastics, identified as low-density polyethylene (LDPE), normal development then reverse development and finally no development resulted with increasing gold. On group II plastics, identified as high-density polyethylene (HDPE), normal development then over-development and finally poor-quality normal development resulted with increasing gold. Our results suggest that the difference between these plastic types causes variations in the gold film structure which in turn dictates the nature of the zinc deposition. On group I plastics, the structure and thickness of the gold film has been identified as the critical factor in the occurrence of normal or reverse development. Thin gold films on plastic substrates form small `clusters (or agglomerates) rather than the atoms being uniformly spread over the surface. The size and shape of these clusters is critical. Once the clusters reach a certain morphology, they no longer act as nucleation sites for zinc, and hence, zinc will not deposit onto the substrate.
Please use this identifier to cite or link to this item: