Advances in Fingerprint Technology.pdf

ehavior of Ruhemann’s purple-metal complexes of various ninhydrin analogues.
157 As noted earlier, Joseph Almog reviewed this material in the previous
edition 133 and presents the current information in Chapter 5 of this
volume.
Development of Latent Prints With Metal
Ions/Compounds — Physical Developers
Silver Nitrate Reagent
Silver nitrate has been used for developing latent fingerprints since 1891. 1
The basic principle of this technique is the reaction of silver nitrate with the
chloride present in the fingerprint deposit. The product of this reaction, silver
chloride, rapidly turns black on exposure to light. However, because the
procedure is cumbersome and the background can stain, this method is
principally of historical interest today.
Goode and Morris6 have suggested using a methanolic solution instead
of the conventional aqueous solution. This method works well with latent
prints on newspaper and untreated wood. However, silver nitrate reagent
does not work well with physical evidence that has been stored or exposed
to high humidity. Under conditions of high humidity, the chloride in the
latent print deposit migrates by diffusion. Researchers have shown that significant
deterioration occurs after 15 days at 60% relative humidity. Prints
weakly developed with silver nitrate may be enhanced by further treatment
with dilute physical developer. 9
Other Silver-Containing Compounds
Kerr, Westland, and Haque158 have studied the perchlorate, tetrafluoroborate,
and hexafluoroantimonate salts of silver as well as silver perchlorate/camphor
as alternative reagents for silver nitrate solution. These compounds were
effective, and the studies indicated that the silver salt reaction with the chloride
in latent fingerprint residue was dependent on the microroughness of
the surface.
Physical Developer
Physical developer enhancement is a photographic process based on the
formation of silver onto a latent fingerprint image from a ferrous/ferric redox
couple and metal salt mixture. Goode and Morris 6 have reviewed the early
work on techniques using “stabilized” physical developer 31 and found that
physical developer reacts with lipid material present in the fingerprint residue.
The technique has been used to develop latent prints on paper, nonabsorbent