Abstract:
This study investigated fingerprint development on five different polymer substrates using vacuum metal deposition (VMD).
The conditions required for optimum development are shown to depend on a number of factors. No one set of conditions will
result in good development in all situations. Polymer type has been confirmed as a major factor in determining the types of
development that will occur and the optimum VMD conditions required. For more consistently successful VMD development,
polymer type should be determined before selecting conditions. While polymer type is a key factor in determining optimum
development conditions, there may be variation of the optimum conditions within a polymer type, most likely due to the
presence of additives in the plastic. The heaviness of a latent print, i.e. amount of residue that constitutes the print, also affects
the VMD conditions required. The donor, manner of deposition, and age of a print affect the heaviness of the deposit. The
heavier the print, the higher the gold count necessary for successful VMD development. The occurrence of ‘empty prints’ (i.e.
zinc deposition on the general background but not on or between the print ridges) was found to be related to polymer type and
print heaviness. Heavy prints on PVC and PET are the most likely to be ‘empty’ after VMD treatment. The development of
empty prints may be due to the diffusion of print residue into the print valleys. Pre-treatment with cyanoacrylate fuming was
also found to affect VMD development. In particular, it was shown that cyanoacrylate pre-treatment was beneficial for print
development on PET and PVC. The results of this study were used to formulate guidelines for use as an aid by laboratories
using VMD in casework.
