General Study Guide - Ontario Police College

Procedures for conducting an examination:
Conduct an examination in a dark room
Aim expanded beam of light at object
View object through an orange barrier or other appropriate coloured filter
Preserve latent prints by photography
The ability to detect fingerprints by fluorescence is dependent on three principal factors:
1. The illuminating wavelength (or Excitation filter) must be appropriate to provide maximum
fluorescence contrast between the fingerprint and the background; i.e. the correct
wavelengths must be available for the chemicals involved, and there must be no significant
stray light at the wavelengths at which the fluorescence is being viewed.
2. Viewing or Barrier Filters include filters for goggles*, viewing housings and cameras (which
must be selected for the chosen excitation filter before allowing light to be emitted from the
forensic light source). The viewing filter must be suitable for protecting the eyes against the
incident radiation, transmit the fluorescence, and where appropriate, separate the
background and fingerprint fluorescence. It will completely block the excitation light, while
allowing as much of the fluorescent emission through as possible.
3. The system must produce an intensity of illumination at the surface high enough to produce
sufficient fluorescence to be effectively observed and photographed.
TYPES OF FLUORESCENCE EXAMINATION:
Fluorescence examination may be used in two principal ways:
As part of an initial examination procedure after a visual examination with white light; and
As an enhancement technique after the application of certain development techniques.
Initial Fluorescence Examination:
With a laser or forensic light source, an initial examination of an exhibit can be carried
out to look for inherent fingerprint fluorescence.
It is frequently unsuccessful
In some cases fingerprints appear darker than the surrounding surface. Generally this
occurs when the fingerprint is contaminated with a material, such as blood, which
absorbs the incident radiation and when the background is a material which fluoresces
under the wavelength being used.
Generally the operator has no way of knowing what the fluorescent materials are, and
therefore no indication of which combination of excitation wavelength and viewing filter
is going to be most effective.
Experience with different surfaces, types of scenes and excitation and emission
wavelengths will provide better guidance in the future, if comprehensive records are
kept of all examinations, successful or otherwise.