A latent fingerprint is a fingerprint that is not visible in its original condition. It requires some form of enhancement or development to make it visible. The development may be as simple as changing the lighting under which it is viewed. Depending on the surface on which the latent fingerprint is deposited, physical or chemical methods may be needed to separate the fingerprint from the background. The most basic and common method of development is the application of finely ground black powder with a specially designed brush. The students will be using this method to develop latent prints from a variety of surfaces in class. They will also be lifting the prints and placing them on cards for identification.
Chemical methods to be used in class will take advantage of the individual components of the fingerprint material. Vitamins, salt, and even amino acids can be isolated to make fingerprints visible. Special wavelengths of light can also be applied to cause fluorescence reactions to occur. Latents can be found and developed on many unusual surfaces.
Processing techniques for classroom laboratory experiments
Black powder - for smooth nonporous surfaces, fine grained powder, filament brush, attaches to moisture
Magnetic powder - for textured, porous surfaces, iron filings, applied with magnetic wand
Protein stain - attaches to materials inside the cells, purple, uses acidic delivery chemistry
Ardrox - stains the fats in the print deposit, yellow fluorescent dye, ALS and UV sensitive