Evaluation of the dimethylaminocinnemaldehyde contact transfer process and its application to fingerprint development on thermal papers

The use of dimethylaminocinnemaldehyde (DMAC) as a fingerprint development reagent was first proposed in the 1970s as a solution-dipping technique to target the urea constituent of fingerprints. However, in operational trials, the quality of developed fingerprints was poor. This was attributed to diffusion of urea with time, and the technique was not pursued. More recently, the use of DMAC fuming and the use of sheets impregnated with DMAC solution have been proposed as alternative fingerprint development processes for porous surfaces, in particular for thermal papers. This study reports an analysis of the DMAC development process using impregnated paper sheets and compares its effectiveness to other techniques proposed for thermal papers. The study concludes that the DMAC transfer process primarily targets amino acids in the fingerprint, but that these may be less persistent than the constituents targeted by ninhydrin and DFO; consequently, the effectiveness decreases more rapidly as the fingerprints age. Overall, the most effective process for thermal papers if it is not necessary to retain the text is an ethanol pre-dip followed by DFO.