Chemical Processing Methods
Oily or greasy latent prints, prints in blood, prints on metallic surfaces, prints on skin, and prints on adhesive surfaces are all special circumstances that require specific chemical processing reagents. For prints in grease or oils, natural yellow 3 and white powder suspension are used on nonporous dark or patterned substrates; Sudan black is used on both nonporous and porous, light colored substrates; and oil red O is used on porous, light colored substrates. For prints in blood, acid yellow is used on nonporous dark or patterned substrates; amido black is used on both nonporous and porous light colored substrates; and acid violet is used on porous, light colored substrates. Metallic surfaces, such as firearms, are processed with cyanoacrylate fuming and dye staining. Gun bluing reagent can be used to develop fingerprints on cartridge casings. Latent prints on skin are not often effectively developed. Adhesive substrates are processed with powder suspensions. Thermal paper is processed with nonpolar formulations of porous fingerprint processing reagents.