Fingerprints were used to “sign” documents as early as 1000 BC by the Babylonians and Chinese! But the science of fingerprint indentification and detection boomed in the late1800s and early 1900s. Thumb impressions were used in India to identify workers by Dr. William Herschel. Dr. Henry Faulds was the first to publish a suggestion that fingerprints could be used for identification purposes. Sir Francis Galton published the first book of fingerprint classifications. Sir Edward Henry reformed the classification system into the one that is used today in most English Speaking countries. New York was the first to use fingerprints in official civil service matters in 1901 and the FBI established the first fingerprint database in 1930.
Now, new techniques for identifying fingerprints on many types of surfaces and for using computer databases and automated methods of comparing and identifying prints are being used and developed. This includes the use of lasers and luminescence in advanced technologies.
Fingerprint detection and identification is a biometric process, where those factors that are unique to an individual are examined, measured and tested. Fingerprint detection can involve finding ways to determine if a fingerprint impression that is sufficient for identification was left on a surface, determining ways to make an impression of a fingerprint so that it can be photographed or the image can be stored in a computer and compared to others, and other complex issues.
The goal is to be able to examine the “minuitae”, or fine details of the print. In many cases, the minutiae must be enhanced by highlighting ridge and furrow detail, filling in for missing sections or otherwise using algorithms to improve the quality of the print without presenting false information that can make the identification faulty.
There are three types of prints: latent, or invisible; patent, or visible to the naked eye; and plastic, or from the palm, toes or foot. Patent prints are generally applied with a substance such as paint or blood. Latent prints have some form of natural skin secretion, such as oils.
But first, the fingerprint has to be detected and this process is called dactyloscopy. The traditional methods were to “dust” the likely area with a substance that enhances the ridge detail for photography. Patent prints can generally be photographed. But latent prints require a developing agent that is sensitive to the chemicals, salts or organic substances in the skin and even the hair and face, since people touch those places and have those secretions on their hands. The adult has more waxy oils than children, for example, making children’s prints less likely to remain viable over time.
The most common chemicals are Ninhydrin, Diazaflourenone and Vacuum metal deposition. These methods may be used on scene or in the laboratory. Now that there is DNA analysis, one problem is the conflict between having to swab and essentially destroy a scarce print for DNA analysis or whether to take the print for identification purposes at the scene of a crime.
The newer methods of detecting and enhancing fingerprints include Micro X-Ray Flourescence or MXRF, which detects sodium, chlorine and potassium in the salts that are in sweat. The salts are sodium chloride and potassium chloride, and can produce an “image” of a print where the substances have been left behind by the ridges. The contrast between the ridge and the furrow can allow a reasonably detailed image of a latent fingerprint.
Finally, flourescent dyes, certain types of inks and other substances can create sufficient images on difficult surfaces by reacting with the amino acids that are left behind when people touch objects. When light at the opposite end of the spectrum from the ink or dye is applied, the substance flouresces, creating an image. Ongoing research into the viability of these methods will hopefully lead to detection of latent prints on many surfaces that have certain flourescent dyes, inks or agents incorporated into them
In summary, while there are many traditional methods of fingerprint detection, with about 20 of them being used most commonly, the advances in creating viable images of ridge and furrow detail continue to allow detection on more surfaces than before, as long as the DNA swab does not take precedence, destroying the print in the process.
“History of Fingerprints”
“Fingerprint Identification”
Wikipedia, “Fingerprints”
About.com, “MXRF”
University of Technology, Sydney, “A New Light On Fingerprint Detection”
