How do you collect fingerprints?

Answer 1

Fingerprints form naturally during the development of the human fetus, starting about 13 weeks after conception. The inner surfaces of the fingers and the palms of the hands, which are covered with hairless (glabrous) skin, develop tiny 'pods', which are the precursors of the pores of sweat glands. These pods, or ridge units, expand and coalesce with neighbouring pods, producing roughly linear ridges, with the sweat pores distributed along their crests, raised above the surface of the surrounding skin. These form the familiar parallel and swirling ridges and intervening furrows, the exact pattern of which is determined by complex, irregular stresses in the skin.

An excerpt from Answers.com on fingerprint origin

Answer 2

Depending on the type of fingerprint, different methods are used: Latent fingerprints, or "Invisible Prints", are most common and detected with:

-Hard/non-absorbant surfaces: Fingerprint powders are dusted over the surface, sticking to the oils of the print. (Powders are made in different colors to provide contrast with the surface being dusted)

-Light color surfaces: Fine Carbon Powders

-Dark Surfaces: White Aluminum powders

-Fluorescent powder may also be used, photographed under a UV light, stands out on bright surfaces

-Soft/Porous surfaces: Chemical methods reveal latents such as Iodine Fuming (Article is placed in an enclosed cabinet with iodine crystals. Cabinet is heated and iodine vapors are released. Once combined with oils of print, chemical reaction occurs and print is visible.

-Ninhydrin Srays form purple/blue color when combined with Amino Acids in human perspirations.

Plastic Prints are pressed into Soap, Wax, or puttys and retains the image of the ridges.

I hope that helped somewhat!