General Study Guide - Ontario Police College

For use on CA-treated prints, the liquid is diluted by a factor of 100 or more with methanol
or water. As with the R6G or BY dye, exhibits can be dipped or sprayed, with dipping being
the recommended method.
In the case of all three dyes mentioned above, excess stain can be rinsed off the exhibit with
the pure solvent or a gentle stream of water. Since the dye is not chemically-bound,
vigourous washing can actually remove all of the dye from the latent print as well. This can
be used to advantage if, for example, the background has absorbed a significant amount of
dye, since more aggressive washing can then be used to attempt to clear off more of the
dye. Exhibits can always be re-treated, if washing has removed too much dye. Most
workers seem to agree that a more dilute solution results in less background interference.
Exhibits rinsed with alcohol will usually dry more quickly with fewer spots.
1,8 Diazafluoren-9-One (DFO)
An amino acid reagent for detection of fingerprints on paper and some other porous
surfaces.
Produces a coloured and fluorescent product on reaction with amino acids and some other
components in fingerprints.
Colour is weaker than ninhydrin, but the fluorescence is, however, so strong that the use of
this reagent in conjunction with a fluorescence examination system will generally produce
many more fingerprints than ninhydrin alone would produce.
DFO is dissolved in a mixture of methanol and acetic acid, then diluted in a carrier solvent.
Paper exhibits are dipped in the solution, then allowed to air dry. A second dip has been
recommended. After the exhibit has dried, the DFO reaction can be accelerated with dry heat.
If immediate results are not required, the preferred development technique is to allow the
exhibit to stand at room temperature for a few days.
DFO-treated prints will fluoresce when excited by blue or blue-green light from a forensic light
source, with the use of a suitable filter required to observe the fluorescence. DFO fluorescence
can also be excited by longer excitation wavelengths. Use of green excitation light and red
viewing filters can be useful on surfaces that are themselves somewhat fluorescent.
Ninhydrin
There are two methods of using fluorescence to enhance ninhydrin developed fingerprints:
o 1) Excite the fluorescence of the background to increase the contrast against the
non-fluorescent ninhydrin fingerprint
o 2) Produce a fluorescent derivative of Ruhemann’s purple by means of treatment
with a heavy metal salt – zinc chloride is normally used and this is referred to as zinc
toning.