Visualizing Fingerprints on Metals

Forensic scientists at the University of Leicester and the Northamptomshire police have discovered a new way of taking fingerprints at a crime scene. Their study is based on the way fingerprints corrode metal surfaces. First, a fine granular conducting powder is coated onto a metal, such as a gun or bullet, then an electrical charge of about 2,500 kv is applied. This attracts the powder to the slight corrosions on the metal left by the fingerprints. The corrosion process depends on the chloride ions present in the sweat excreted by the individual. The water content of the fingerprint residue acts as an electrolyte to permit the glavanic corrosion to take place on the surface of the metal. This chemical reaction takes place at about 600 degrees Celsius. The degree of enhancement of the fingerprint depends on the composition of the metal and the level of salt secretion by the person who left the fingerprint.

According to Dr. John Bond, the honorary fellow at the University of Leicester and the scientific support manager at Northamptonshire police, "Wiping down, washing it (the weapon) in hot soapy water makes no difference- and the heat of the shot helps the process we use." This technique helps solve the difficult problem of enhancing a fingerprint on a small calibre metal cartridge case that has not been fired. The scientists also indicate that the print never disappears, so past cases could be re-opened for investigation and use this technique. The only way to avoid the fingerprint from being detected is through abrasive cleaning which strips the top layer off of the metal. Dr. Bond and his colleagues at the university plan to take this research forward by further exploring the corrosion of metal by fingerprint residue and how it can be used more efficiently in investigating crime scenes.

www.sciencedaily.com/releases/2008/06/080602103331.htm

http://www3.interscience.wiley.com/journal/120120709/abstract/?CRETRY=1&SRETRY=0

www.le.ac.uk/forensic-research/fingerprintresearch.html