Developed latent fingerprint impressions on adhesive surfaces are often difficult to photograph without excessive diffused highlights. The reason is that the surface of many tapes such as strapping tape or duct tape is not perfectly flat. Numerous small surface irregularities (texture) scatter light creating unwanted highlights in the photograph. The use of water can often help increase contrast in latent prints developed on adhesive or other textured surfaces. These developers may include: crystal violet, Coomassie blue, and others. A photographic procedure was developed by Beverly Naccarato, of the Spokane County Sheriffs Identification Unit, that effectively controls these unwanted highlights.

Procedure:

Utilizing a standard photographic copy-stand adjust the lights to 45°. Set the camera lens for 1: 1 (life size) and include any necessary contrast enhancement filters. Use a syringe with a blunt needle to apply a large drop of water to completely cover the developed print or section of print to be photographed. Then add water and/or adjust the lights to ensure the specular highlights of the light sources do not interfere with the fingerprint. The final step is to photograph the print.

The more water that is added to the print, the further the specular highlights reflecting off the water will move away from the fingerprint in the center of the photograph. In fact, if the lights are set correctly the specular highlights will be located at the edge of the water bead that covers the print. The refraction qualities of the water drop will effectively control the diffused highlights from the textured surface on which the print may reside. (See Illustration).

The photograph shown for this illustration is of a Coomassie Brilliant Blue® developed fingerprint on the adhesive side of duct tape. It was photographed by Beverly Naccarato using a Olympus OM-4t camera with a 50mm macro lens extension tube for a 1: 1 photograph. The film is Ilford B&W XP2 film set to an ISO of 200. A dark line was added using Photoshop to illustrate the division between the water and the dry tape surface.

The concept of controlling the refraction qualities of the light source(s) with water may also have other applications. The general result of using a drop of water for refraction control is that contrast is increased thus making the developed fingerprint more visible.

WATER DROP USED TO CONTROL LIGHT REFLECTION ON A TEXTURED SURFACE.