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| 3 Ways to Collect Fingerprints |
By:
Chris Sturat |
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There are many ways of collecting fingerprints, but three of the general ways are with the use of powder, chemical, and fuming. The oldest, yet most commonly used method to collect latent fingerprints is with powder. This is done by dusting a non-porous surface with fine powder that is of a contrasting color. What happens is that the powder is able to adhere to sticky or greasy substances, which latent fingerprints have. Then, the investigator will be able to apply and dust off the loose powder, and then use a sticky tape to lift the powder print off. Unfortunately, this method works best with relatively fresh fingerprints. Also, if the nature of the surface and the composition of the print are different, it will be hard to get the print. Many different powder and brushes are available, but the best ones will be in a contrasted color, can adhere well with the residue, and is sensitive. Then, using a lifter, the latent fingerprint is lifted up before it is adhered to a transparent protective plastic sheet.
Another way is with the use of chemicals, like iodine, ninhydrin, or silver nitrate, but only with porous objects. With iodine, the chemical is heated up in a fuming chamber, releasing iodine fumes that will interact with the oil found in the latent print, producing a brownish-colored fingerprint. The print is then captured on film or sprayed with a water-starch solution to make the print last for a period of time. With ninhydrin, the object would be sprayed with the ninhydrin solution that will react with the oils of the latent print. It takes a long time to produce the purple-blue print, but by heating the object up, the reaction time is reduced. For silver nitrate, application of it on the object will cause the chloride in the latent print to interact with the silver nitrate to form a reddish-brown silver chloride fingerprint, but can only be seen under UV light.
Last but not least is through fuming cyanoacrylate. Unlike the previous two methods, this can be done with both porous and non-porous surfaces, and does not disturb the object that is tested. What happens is that cyanoacrylate, which basically makes up about 98% of the active ingredient of Super Glue, is poured onto a metal plate which is then heated to 120 Fahrenheit, or it can be mixed with sodium hydroxide (NaOH), which will create the same intended effect. Then, along with the object for inspection, both are placed in an airtight chamber together. The heated or mixed compound will then release cyanoacrylate fumes which will make the latent print visible, as the fumes would interact with the amino acids in the fingerprint residue, creating a visible white print that can be captured on film or be treated with a fluorescent pigment. Nevertheless, there are many other ways of collecting fingerprints that are available or is in development to help make crime investigations more effective.
Chris is writing and sharing articles on wide range of topics related to ways of collecting fingerprints and fingerprint scanners. Visit to read more detail.
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