General Study Guide - Ontario Police College

Wet, Non-Porous & Porous Surfaces – Types and details of chemical processes in proper development sequence – depending on circumstances not
all processes may apply. All processes, however, are post visual and examination of inherent fluorescence by laser or alternate light source.
Development Techniques and ‘Basics’ of Processing Procedure
1. Small Particle Reagent (S.P.R.) (a.k.a. Powder Suspension)
A reagent for latent print processing of non-porous items that
became wet after the impressions were deposited. Suggested for
use on items where latent print powders are ineffective. Not
suggested for items contaminated with greasy substances.
Can be used post-cyanoacrylate when dye stains are ineffective.
The active ingredient (Molybdenum disulfide) is applied either by
spraying or dipping.
Rinse with tap water & dry at room temperature. Prints are more
visible when they are dry.
Photograph any developed detail and then you may try lifting the
dried print.
Latent Print
Development
Colour
Dark grey
Ridge Detail Visualized By
The SPR technique relies on the adherence of fine
particles suspended in a treating solution to the fatty or
oily constituents of latent fingerprint residue.
(Formulated mid 1980s) Accordingly, it may be regarded
as belonging to the same family of methods as powder
dusting. SPR consists of a suspension of fine
molybdenum disulfide particles in detergent solution.
2. Silver Physical Developer (Ag-PD)
First formulated in 1975 by the British Home Office Police S.D.
Branch.
PD is a surfactant-stabilized solution containing silver ions, a
ferrous/ferric redox system, a buffer (citric acid) and detergents
in an aqueous solution.
PD is used for the development of lipid type (oily,greasy)
impressions on porous surfaces. (OPC)
PD works well on clay fire bricks, concrete, latex or rubber gloves,
both sides of adhesive tape, rayon or nylon clothing, unfinished
porcelain, unfinished wood and wooden knife handles.
(A.F.T.pg.136)
Dark Grey
It’s water-based and thus it visualizes the waterinsoluable
portion of the latent print residue. These
components include fats and oils (lipids) but also waterresistant
proteins, lipoproteins, and even water-soluable
components (amino acids, proteins, urea, salts etc.) that
get trapped in the lipids as they “dry” and harden
through oxidation.