Latent Print Photography

Minutiæ Issue #46

Latent Print Photography - Pat A. Wertheim

This article is the fifth in a comprehensive series of articles on latent print development techniques written by Pat A. Wertheim, Director of Training for Forensic Identification Training Seminars, Ltd. Watch for future articles in each issue of Minutiæ and save these issues in a binder to compile a manual of fingerprint development techniques.

In the early days of latent print science, clear adhesive tape had not yet been invented and the only way to record a latent print was by photography. Of course, the 35mm SLR camera had not been invented, either, and the camera of the day was the 4" x 5" sheet film camera. Because of the training required to use those old cameras, it was far easier to hire a trained photographer and teach him latent prints than to hire someone who knew neither fingerprints nor photography. Even though black and white was the only film available, colored powders were selected to provide maximum contrast with the background on which the latent was developed, and colored filters were used to enhance that contrast. Excellent images resulted. Latent print photography by those standards is all but a lost art.

Large format, 4" x 5" cameras are still used in most major fingerprint laboratories, the Polaroid MP-4 being the most common camera of this type in use today. Although the MP-4, or any other 4" x 5" camera, is capable of refined fingerprint photography techniques that are difficult with a smaller format 35mm, some of these techniques may actually be used with a 35mm with a little effort and practice. One point to keep in mind, however, is that frequently, fingerprint photography requires the use of light in ways not used, or even avoided, in other types of photography. The following three methods may be used with either the large format cameras or small format cameras. With a 4" x 5" camera, pictures would be taken at 1-to-1 scale. With a 35mm, they should be taken with the closest focal range possible and the smallest ƒ/stop to maximize depth of field, using long exposure times and focusing by moving the camera closer or farther from the object as needed for correct focus. As much as possible, a 90° angle should be maintained between the camera direction and the surface being photographed. Neither type camera should be hand held for fingerprint photography, but must be mounted firmly on a copy stand or sturdy tripod.

The most common method used is photography by "direct light." This method of fingerprint photography is used for fingerprints of good contrast plainly visible to the naked eye. The camera is aimed straight at the fingerprint with one or more light sources shining from about a 45° angle. In reality, this is simply normal photography, the same way you would photograph people or scenes.

The second most common type of fingerprint photography is with "direct reflected light." This method is used for prints that you can see only by manipulating the surface to catch the glare of some light source. The camera is aimed at the surface in a manner to catch the fingerprint image highlighted in the glare. This method is especially good on perfectly flat, shiny surfaces. For example, it works very well on plastic garbage bags after glue fuming when the fingerprints have not come up in well-developed white prints. Stretch the area of plastic with a print tightly over a beaker or end of a can to hold it flat, securing the plastic firmly with a rubber band to keep it stretched. Focus down on the print, using an overhead ceiling light to provide the necessary glare to highlight the print.

The third method is with the use of what might be described as "oblique transmitted light." This method is particularly good for photographing glue-fumed prints on clear plastic film such as cling wrap or plastic baggies. Stretch the clear plastic material over a glass beaker or wide mouth jar with the print centered over the opening, again using a rubber band to hold it in place. Cut out some various sized circles of black paper, from 1" diameter to 4" diameter. If a light table is available, place an appropriately sized black circle on the table under the beaker, so that the light is blocked from the print itself in the view of the camera. This will produce a crisp white fingerprint on a black background. If no light table is available, some experimentation and imagination may be required to figure out how to get the light source to shine through the plastic material with the black background under the print, but the results will be worth the effort.


In the next issue of Minutiæ, Pat will write about using iodine and silver nitrate to develop latent prints on porous surfaces.