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A number of methods have been developed over the years to help detect fingerprints.

Iodine fuming

This is the oldest of the chemical methods for detecting fingerprints. Solid iodine sublimes (becomes a vapour without becoming a liquid) at room temperature. If an object, say a piece of paper, is placed in a chamber which a has had some crystals of iodine placed in it, any fingerprints on the object will appear as brownish prints. What is thought to be happening is that the iodine vapour is dissolving in the skin oils (or may be the traces of water from the perspiration) that make up the print. Whatever is happening the print is temporary and will soon fade. It  must therefore either be photographed immediately  or "fixed" by spraying with starch solution to give a blue print which will last longer.

Ninhydrin

Iodine fuming has to a great extent replaced by other methods including spraying with the chemical ninhydrin which reacts with amino acids present in the skin secretions to give purple prints.

Superglue

The active ingredient in superglues is a cyanoacrylate ester. When vapours of these compounds come into contact with fingerprints the molecules of the cyanoacrylate attach to the print and polymerise. The visible prints produced are white, to improve their detectability they are often treated with a fluorescent dye, such as Rhodamine 6G, before being photographed under an special light source or a laser.

For more information concerning the development of Latent Prints visit Latent-Prints.com, a discussion forum with  a number of articles on the detection and interpretation of latent fingerprints.

Luminescence and Fingerprinting

Some molecules when irradiated with certain types of light fluoresce, the phenomenon is called luminescence. Researchers discovered some years ago that some components of sweat are luminescent and fluoresce when illuminated with lasers;

Follow this link to find out more about luminescence and its application to forensic science;

Luminescence

There are disadvantages in using lasers as they are expensive and there are significant safety issues to consider. With the advent of treatment of fingerprints with fluorescent dyes (see above), the use of so-called alternate light sources which are essentially high intensity lights has increased as they are less expensive, safer and more portable than lasers. Examples of the sort of prints that can be visualised using alternate light sources in conjunction with fluorescent dyes are shown below;