Techniques/ Chemicals Used in Developing Fingerprints

Lifting fingerprints from a crime scene is a crucial step in determining a possible suspect. Fingerprints that are on hard and nonabsorbent surfaces are usually developed with the application of a powder. Examples of hard and nonabsorbent surfaces are, mirror, tile, glass, and painted wood. While for soft and porous surfaces they can be made visible with the treatment of a chemical. Examples of soft and porous surfaces are cloth, paper and cardboard.

When using a powder to develop a fingerprint the powder of choice is usually the one that has the best contrast with the surface while it is being examined. The black powder used in examining fingerprints is generally made out of black carbon or charcoal, and is applied to white or light-colored surfaces. The gray powder that is composed mostly of an aluminum dust, is used on darker colored surfaces; it can also be applied to mirrors and metal surfaces that have a polished look. These powders are usually applied lightly to a nonabsorbent surface with the use of a fiberglass or a camel’s-hair brush. Another powder that some people use is a magnetic-sensitive powder that is spread with a magna brush, a magnet in the form of a brush. Some investigators use fluorescent powders that can be seen under black-lights.



Fingerprint being developed by the dusting technique.

Chemicals can also be used to visualize latent prints; the oldest and most common method used is iodine fuming. Other chemicals that can be used in this process are silver nitrate, ninhydrin powder along with a suitable solvent (such as acetone or ethyl alcohol), super glue fuming, and many other types of chemicals.



Fingerprint developed by iodine fuming.