Traditional Methods of Latent Fingerprint Recovery

The latent fingerprints are invisible marks left in the crime scene. It is undetectable until the latent print is converted into visible form. Therefore, the preliminary task of the forensic scientist is to convert the hidden finger mark into visible print. There are various techniques of latent fingerprint recovery. Hereby, we discuss three popular techniques of fingerprint visualizations. Powder Dusting: It is the most popular method of extracting fingerprints from crime scene. Powder dusting is a perfect example of physical technique of fingerprint extractions from a solid surface. Two types of powders are used for getting the fingerprints. One is regular powder that is used in the non-shining surfaces like table top, doors and television. Another is magnetic powder that is used in shiny surface like glass and plastic containers. Fingerprint powder is available in different colors. The choice of color depends on the color of the surface. White powder is used on a black or deep colored surface and black powder is used on light surface. Powders are poured on the surface and spread apart by a light brush. An impression of the fingerprint is formed on the surface and the print is lifted by adhesive tapes. Super-glue fuming: It is also known as super-glue fume technology. The oil and sweat contain amino acid, glucose, ammonia and other organic compounds. The principal theory of super-glue fuming technology is to apply Cyanoacrylate that reacts chemically with the organic constituent of the oil and sweat. Cyanoacrylate is a colorless chemical that is easily polymerised and used as powerful glue. The chemical is also known as super-glue. The super-glue and the suspect material are kept in an airtight container. Super-glue-fumes are created by heating at 120-140 degree temperature. The fume reacts with the organic constituent of oil and perspiration those are ejected from finger. Chemical reaction forms the impression of latent fingerprint. Iodine fuming: It is one of the oldest scientific method of latent fingerprint recovery. Though the process of latent fingerprint extraction of super-glue fuming and iodine fuming are almost similar, yet there is a basic difference between the two technologies. While the super-glue fuming technology depends on the chemical reaction of super-glue materials, the iodine fuming is based on the physical properties of iodine. In iodine fuming, the oils and fats absorbs the iodine vapor temporarily and that results the change of the color, from clear to dark brown. However, the change begins to fade within a short period. Therefore, 1% starch solution with water is sprayed to convert the dark brown color into blue. The changed color generally lasts for one or two weeks. The contrast of the fingerprint impression creates well contrasted image of latent fingerprint.