Fingerprint powder is a very fine powder which is designed to adhere to the traces of oil, sweat, and other materials left behind by the friction skin on the fingers, palms, and feet. When fingerprint powder is applied with care, it can be used to develop latent prints; in other words, it makes the prints visible so that forensic technicians can record them and use them in a criminal investigation. Several firms manufacture fingerprint powder, with a range of types of powder being available to investigators.
As a glance at your palms will reveal, the skin on your hands is very different from the skin on other parts of your body, and the same holds true for your feet. This finely ridged skin is known as friction skin because it increases friction, allowing people to manipulate objects and their environment more easily. The distinct ridges and whorls on the hands and feet form in the womb, and they remain consistent throughout someone’s lifetime, unless he or she is badly injured, in which case the scarring will mar the prints.
When people touch things, they leave behind a residue of material. By using a powder which adheres to this material, it is possible to see a print of the person’s hand, palm, or foot. This print can be used to identify that person, linking him or her to a crime scene. Fingerprints have been used in forensic investigation since the late 1800s, and they are probably one of the most familiar aspects of forensics to many civilians today.
The formulation of fingerprint powder is important. Light powders are used to develop prints on dark surfaces, while dark powders stand out against light surfaces. Some investigators use fluorescent or brightly colored powders to bring out more detail. In all cases, the fingerprint powder has to be very fine, and it must resist caking. It can be applied with a delicate brush or by blowing the powder across the surface to be fingerprinted. Some forensic technicians use magnetic powder, which utilizes an applicator that will not directly touch the fingerprint.
Fingerprints will not show up on all surfaces with fingerprint powder. Smooth surfaces tend to be the best for fingerprinting. More rough surfaces can still sometimes be fingerprinted by fuming, which involves vaporizing substances such as glue and wafting them over the surface, allowing the substance to adhere and bring out fingerprints.