Chemical Techniques

Utilizing various chemicals to develop latent fingerprints allows the investigator the ability to potentially develop prints on any surface if the conditions are right. Which technique to utilize will be dictated by the knowledge and experience of the investigator, as well as the item or surface to be processed. What must be emphasized is that utilizing a specific technique may produce different results in different environments.

When attempting to develop latent prints, there are no absolutes. Remember, latent prints are chance impressions on a surface.

Figure 5.28 Latent tape and processed fingerprint.

Chemical reactions are a result of substances contained in the perspiration or on the friction skin being transferred from the friction skin ridges to the object. Chemicals such as salt (chloride), protein, amino acids, lipids, and oil react with the chemicals to reveal the latent prints. Other substances might include blood, grease, or food stuffs.

Whatever chemical technique that the technician chooses to use it is important that this technique does not deter from other processing or analysis to be completed (such as DNA). Be sure you understand the usage, hazards in utilizing such chemicals. Asking the manufacturer or the latent examiner will help prior to utilizing chemicals.

Fluorescent Powders

Fluorescent powder is implemented when the surface that contains the possible latent fingerprints are dark or multicolored such as soda cans.

Figure 5.29 Lifted fingerprints on latent fingerprint card.

Black latent cards are effective for placing the tape with the lifted fluorescent fingerprints.

These powders may be used in place of traditional powders or in conjunction with other techniques such as Super Glue (cyanoacrylate). These powders tend to be much finer and produce the best results when used with a feather duster rather than the traditional fiberglass or camel hair brush. The advantage of this technique is that, due to the fine powder composition, less activity is required to develop latent prints, thus lessening the likelihood of destruction of the print. The disadvantage is that with this technique additional luminescence is required in the form of an alternate light source (ALS) or light amplification by stimulated emission of radiation (laser) to make the print usable. Lights with a filter barrier may be used to detect the prints in lieu of the ALS or laser. The prints developed with this method must also be photographed. These powders may be used just as traditional powders are.