Examination of Firearms Review: 2007 to 2010 - Interpol

gel lifter, followed by a white one. When the lifters where taken to the authors’
laboratory and photographed, the photographer noticed by coincidence that
although the prints on the gel lifters were quite poor, there were distinct prints on
the transparent protective plastic sheet of each of these lifters. Interestingly, the
second (white) lifter showed a better print than the first (black) one, probably due
to the removal of interfering background by the first.
2.1.4 Chemical Enhancement
The HOSDB 2008 newsletter mentioned above (9) contains also a summary of
methods for enhancement of shoeprints made of various substrates. The methods
tested in this study were those routinely used for latent fingerprints development. It
is interesting to note that a powder suspension was very effective on most
contaminants, and was the single most effective process on 50% of the tested
contaminants.
McNeil and Knaap (28) compared the performances of the bromophenol blue
(BPB) indicator with those of potassium thiocyanate for the enhancement of dust
footwear impressions. These authors found that BPB performed better than
potassium thiocyanate on most shoeprints tested.
2.1.6 Shoeprints and Tire-tracks in Snow
Taking casts of shoeprints or tire-tracks in snow is more challenging than other 3D
impressions, due the nature of this substrate. The commonly-used dental stone is
not applicable for snow impressions due to its exothermic reaction while curing.
Numerous methods were published over the years for such cases. One of these
methods was to use molten pure sulphur, which is well studied and documented.
There are, however, several limitations in using this method: It requires additional
equipment (a stove and a melting pot) not usually carried as a part of an evidence
collection kit, a respirator is needed due to the hazardous sulphur dioxide fumes
produced, and the produced sulphur casts tend to be brittle. In order to overcome
some of these limitations, Wolfe (29) studied the use of sulphur cement for casting
snow impressions. Sulphur cement is a silica-filled modified sulphur mixture, which
is melted, cooled and poured in the same manner as pure sulphur, but has higher
strength and stability. Validation studies showed that sulphur cement could rapidly
and reliably preserve snow impression evidence with detail comparable to that of
pure sulphur or dental stone casts. Based on this study, sulphur cement proved to
be safer and of higher strength for casting snow impressions, as a substitute for
pure sulphur.
In order to overcome the disadvantages of dental stone for casting impressions in
snow, Adair and Shaw (30) proposed a dry-casting method. When applying this
method, these authors used a commercial flour sifter to sift the dry dental stone
powder onto the impression in fine layers, followed by cold water spraying (using a
plastic spray bottle). The dry-casting method is remarkable for several reasons:
First, the method uses materials commonly carried by crime scene investigators,
namely dental stone and water. Second, flour sifters are inexpensive and simple to
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