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).
[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).