Articles from The Science Of Fingerprints
Establishment Of A Local Fingerprint Identification Bureau
The Tented Arch
In the foregoing instances in which it has been impossible to obtain
suitable inked impressions it will be noted that the last resort has
always been photography. In all probability in advanced cases of
decomposition, desiccation, and maceration it may not be possible to
secure inked impressions which can be properly classified. Hence, it
will be necessary to photograph the ridge detail. Accordingly, there
are outlined below several methods of photographing the ridges which
have been used with success.
In photographing the ridge detail on fingers it has been determined to
be most practicable to photograph the finger natural, or 1/1, size
inasmuch as comparisons will usually be made with inked impressions
which are natural size. Any camera built or adjusted to taking 1/1
size pictures, and with which the lighting may be arranged to best
advantage, may be used.
There is a wide choice of film which can be used for this purpose. The
so-called soft films are all good for photographing ridge detail on
fingers. Process film is not recommended inasmuch as the film presents
too much of a contrast. Consequently, if it is used, some of the ridge
detail will be lost, especially if wrinkles are present in the skin.
Lighting is accomplished by the use of gooseneck lamps, floodlights,
or a spotlight. If a fingerprint camera is used, its lights may be
The manner of lighting may be by direct light, side light, transmitted
light or reflected light, depending upon the prevailing condition of
the finger or skin.
Direct light is used in those cases in which the ridge detail is
fairly clear and there are no wrinkles present; or, if wrinkles are
present, they are not deep enough to interfere with photographing the
Side lighting is used when there are no wrinkles of any consequence
and the ridge detail is clear but because of discoloration the ridges
are not readily seen in the ground glass as there is lack of contrast
between ridges and depressions. Accordingly, the lights, instead of
being focused directly on the skin or finger, are placed to the side
of the object so that the light is directed across the skin or finger,
thus highlighting the ridges and shading the depressions.
In side lighting, two lights may be used. Better results are often
obtained, however, by using only one light, such as a spotlight, the
beam of which can be controlled to best advantage.
Transmitted light is used in cases in which the skin has peeled off or
in which the dermis has been removed, cut, and scraped thin so that
light will go through. The prepared skin is placed between two pieces
of glass pressed together in order to flatten the skin or dermis and
remove creases. By trimming some of the surplus skin or dermis,
especially at the top, it may be more easily flattened. After the
glass is properly mounted in front of the camera, the lights are
placed behind it and light is directed through the skin. The ridge
detail is brought into focus on the ground glass. Before the picture
is actually taken it is suggested that the ground glass be checked by
first using one light and then two lights to see which is more
There will be instances in which the second layer of skin, cut and
scraped thin enough to flatten out, fails when dry to have a
sufficient contrast between ridges and depressions for purposes of
photographing. The same piece of skin when soaked in xylene will show
a marked contrast, which it loses on drying. This difficulty is
overcome by photographing the skin while in solution, which can be
done by placing the skin in a test tube or a small bottle of a size to
keep the skin upright and the ridges toward the camera. The test tube
or bottle is then filled with xylene.
If the skin is sufficiently thin, transmitted light may be used.
Should it be found, however, that transmitted light is not effective,
then direct light may be tried and the results checked in the ground
glass (fig. 401).
When photographing a small curved surface such as a test tube, direct
lighting will usually create a high light. If the high light as shown
in the ground glass is over the ridge detail on the skin, a poor
photograph will result. If the high light cannot be removed by
rearranging the lights, then reflected light should be tried.
In order to effect reflected light a large piece of white paper,
cardboard, or similar material is used. A hole is cut in the center of
the paper or cardboard. This must be big enough for the camera lens to
protrude through. The ends of the paper or board are curved toward the
skin or finger to be photographed. The lamps which are to be used are
placed facing the curved paper or cardboard in such fashion that the
light will strike the paper or board and be reflected by the curved
surface to the object.
The lamps should be close enough to the paper or board to give the
maximum light. Care should be exercised, however, not to place them
too close, because of the fire hazard.
Any arrangement of lamps and reflectors giving a similar effect as the
above should prove suitable.
Fingers or skin which have a mottled, reddish-brown color because of
decomposition, exposure to severe heat, or diffusion with blood
present a problem of lack of contrast between ridges and depressions
for photographic purposes. This lack of contrast can be overcome to a
large extent by the use of a yellow or light red filter. Sometimes, in
those cases where the discoloration is due to the diffusion of blood
throughout the tissues, the blood can be washed out by saturating and
rinsing the specimen in a 10- to 20-percent solution of citric acid.
If, of course, the blood is not removed satisfactorily, the
photographing should be done with the filter.
As previously stated, the fingerprint camera can be readily adapted to
the use of photographing fingers or skin specimens for ridge detail.
Sometimes it is possible to photograph the skin or finger in the same
manner as one does a latent print. There will be instances, however,
in which the standard use of the fingerprint camera will not be
possible or effective, such as for side light, reflected light, and
sometimes transmitted light, or instances in which it is not possible
to get the finger or skin flush with the opening of the camera. In
these instances the lights of the camera are not used, so the
batteries should be removed and gooseneck lamps or other suitable
lighting equipment and ground glass utilized when the finger or skin
is prepared for photographing (fig. 402).
The camera is opened either at the point where the lights are housed
or at the lens point, whichever is most effective. Then, opening the
shutter, the operator moves the camera either toward or away from the
finger or skin to the point where the ridge detail is sharpest in the
ground glass. The camera is held firmly, the ground glass is removed,
the film is inserted and the photograph taken.
With respect to exposure time, it is possible only to generalize and
point out that each case will have its own individual aspects.
Controlling features for consideration will be the type of film, the
type and size of lights, the method of lighting (direct, side,
transmitted or reflected) and also whether or not filters are used.
Accordingly, there may be a wide variation of exposure time in
The best approach for arriving at the proper exposure time is merely
to make a test exposure, develop the film, and from an examination
determine if it is underexposed or overexposed. Time the next exposure
accordingly, until satisfactory results are obtained.
As has been mentioned previously, when photographing the ridges on
fingers or skin, the ridge detail will be in reverse position, the
opposite from an inked impression made from the same skin or finger.
(This is true except in those cases in which the underside of the
epidermis is photographed.) Accordingly, when the negative is
printed, it should be printed gloss side to sensitive side of paper to
give the position comparable to an inked print made from the same skin
or finger. In order to avoid error or confusion a notation should be
made on the photograph of each finger, or, if they are cut and mounted
on a fingerprint card, point out that the position has been reversed
and that the prints are in their correct position for classifying and
searching. Otherwise, it is possible that the right hand may be
mistaken for the left hand and vice versa.
If the underside of the epidermis or outer skin is being photographed,
the negative should be printed in the normal manner, that is, emulsion
side of negative to sensitized side of paper. Here, reversal of
position is not necessary for when the ridge detail is viewed from the
underside it appears to be in the same position as the inked
impression normally is reflected on a fingerprint card.
Care should be taken to see that each photograph is labeled correctly
to indicate the finger it represents, such as right thumb, right
index, right ring, etc. It is imperative that no error occurs in such
labeling, inasmuch as it is highly probable that the resultant
classification would be incorrect and failure to make an
identification might very easily follow.
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