Chemical Visualization of Latent Prints

• NCJ Number: 238008
• Author(s): Evan Durnal
• Date Published: July 2010
• Length: 61 pages
• Grant Number(s): 2008-NI-CX-K012
• Agencies: NIJ-Sponsored
• Publication Type: Report (Study/Research)
• Award: Latent Print Chemical Visualization

Annotation

This study investigated new chemical processing methods for fingerprint development, and three new techniques were developed with the following attributes: non-toxicity and non-irritating, cost-effective, instantaneous ridge visualization (with or without alternate light sources), high-resolution fingerprint ridge detail, minimal pre- and post-treatment requirements, and the capability for visualizing prints on porous and/or non-porous surfaces.

Abstract

The first of the new techniques developed uses a phenolic resin powder that can be substituted for current fingerprint dusting kits. The phenolic resin, a light-pink solid, adheres to fingerprint oils when applied using typical dusting procedures. The dusted print can be immediately observed on dark backgrounds. Further print development was achieved by applying an aqueous solution that contained a Leuco dye, which underwent chemical transitions due to the acidic pH present in the phenolic resin. Phenolic resin can be gelled to create a permanent print; and all chemicals and solutions are non-toxic. The second method is a procedural modification for making metal etching with acidic vapors safer for criminal investigators. A commercial product call Tek Gel, which is used for artistic cement detailing, is a fluorescent gel that contains hydrochloric acid, which slowly vaporizes over time and can be used to etch fingerprints on metal surfaces. The third method uses stains and dyes extracted from natural plant sources in order to visualize fingerprints left on porous surfaces (paper). Several plant-derived stains were used to treat paper, including juglone, lawsone, and osage-orange. All three dye solutions preferentially stain the cellulose used in paper products. The oils left behind from a fingerprint coat the cellulose fibers and prevent them from being stained. 24 figures and 10 tables