Techniques and Chemicals used to Develop Prints on Multiple Surfaces Part One

Fingerprint powders are available in a variety of colors and compositions. The powder of choice is the one that shows the best contrast with the surface being examined.
Experienced examiners find that black and gray powders are satisfactory for most latent print work. Therefore, the black powder, composed of black carbon or charcoal, is applied to white or light-colored surfaces.

The gray powder, composed basically of an aluminum dust, is used on dark-colored surfaces; it is also applied to mirrors and metal surfaces that are polished to a mirror-like finish, because these surfaces will photograph black. These powders are applied lightly to a nonabsorbent surface with a fiberglass or camel's-hair brush, and will stick to perspiration residues and/or deposits of body oils left on the surface.

Another type of powder is the magnetic-sensitive powder that can be spread over a surface with a magnet in the form of a Magna Brush. It also decreases the chance of damaging or destroying the print because the Magna Brush does not have bristles that touch the surface. These powders also come in a variety of black and gray colors. Fluorescent powders can also be used to develop latent prints, which will fluoresce under ultraviolet light.




http://www.bxscience.edu/publications/forensics/articles/fingerprinting/f-fing03.htm