The development of latent fingerprints on polymer banknotes

Polymer (plastic) banknotes have completely replaced traditional paper banknotes in Australia and New Zealand. They are also used in many other countries to varying extents. These banknotes, especially older ones and ones with aged prints, present challenges for latent fingerprint development. A preliminary study examined the effectiveness of a wide range of development techniques but none of the routine detection techniques employed were able to develop prints older than 7 days. In the present study, further research was conducted to optimize a particular development sequence. Australian polymer banknote samples were obtained from the Reserve Bank of Australia. Visual examination of the degree of wear of the printed inks was used to classify the banknotes into five wear categories. Category 1 notes were those with the least wear and category 5 notes were those notes with the most wear. The vacuum metal deposition (VMD) unit used in this research was designed and manufactured specifically for latent fingerprint development. Results show that the recommended procedure for the development of latent prints on polymer banknotes incorporates a particular sequence. The sequence involves optical examination, immediate treatment with cyanoacrylate fuming, examination of the banknote, treatment by VMD, examination and recording of developed prints using diffused reflected light, further treatment by VMD (gold and zinc), luminescent staining, and examination and recording of developed prints. The success of the procedure is affected by the wear of the individual notes. The more worn a note is the less likely good quality prints will be developed