Fluorescence Examination:: As early as 1933, fluorescence examination with UV light was suggested as a method of visualizing latent prints dusted with anthracene powder on multicolored surfaces (Inbau, 1934, p 4). Before the late 1970s, UV fluorescent powder was used occasionally and appears to have been the only credible fluorescent method of latent print detection. In 1976, researchers at the Xerox Research Centre of Canada discovered inherent latent print fluorescence via continuous wave argon ion laser illumination. Shortly thereafter, the first latent print in a criminal case was identified, using inherent luminescence via laser excitation (fingerprint on black electrical tape) (Menzel and Duff, 1979, p 96). Since the late 1970s, advancements in the technology of fluorescence detection have greatly aided the hunt for many types of forensic evidence. Today, evidence that would be barely perceptible or even invisible under normal lighting is routinely intensified by fluorescence. Bloodstains, semen, bruises, bone fragments, questioned documents, flammable residues, fibers, and fingerprints all merit examination with a forensic light source or laser.
To visualize latent prints via fluorescence, a specific bandwidth of radiation must be shone on either an untreated latent print or one treated with a fluorescent chemical. The wavelengths chosen will be determined by the chemical involved and the luminescent nature of the substrate. The evidence is then examined through viewing goggles or filter plates that block the incident light from the forensic light source. These goggles act as a barrier filter and are fundamental in separating the incident light generated by the light source and the weak fluorescing signal emitted by the latent print. This separation of incident and emitted light signals gives fluorescence examination its sensitivity.
