The chemistry of fading Prussian blue fingerprints - Theoretical and experimental analysis of a 'forensic dilemma'

摘要

Latent fingerprint traces can be visualized as negative images using Prussian blue. The process provides detailed fingerprints and can also be carried out in a short period of time using only a small amount of material. When using it on metals such as copper, iron or zinc, one disadvantage of the method is noticeable: the blue negative images fade within minutes, whereby the contrast to the background is reduced and an analysis of the fingerprints becomes impossible. The phenomenon of "fading" Prussian blue fingerprints is the subject of this article. Based on a working hypothesis, model experiments are presented which lead to the verification of the hypothesis and to the conservation methods resulting from it.