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Fingerprint enhancement techniques
Fingerprint enhancement techniques
Powder suspension is a relatively new enhancement technique which is used on non-porous surfaces. It is a suspension of a coloured metal in a detergent solution. Firstly, a brush is dipped into the powder suspension solution. This is applied to the surface in a similar motion to applying paint.
Once coated, the powder suspension is washed off the surface with powder suspension remaining at the fingermark. The item is generally left to dry before any fingermarks are recorded using photography.
Fingermark powders are used to enhance marks on non-porous surfaces. Different metals are used to make fingermark powders. Powders are simply metallic dust, which are applied using a special powder brush. However, some are magnetic which need to be applied using a magnetic applicator. Different powders are recommended for use on different surfaces, such as aluminium powder is most effective on glass and black magnetic powder is most effective on UPVC. The powders adhere to the substances that are present in the fingermark. Once visualised, powdered fingermarks can either be photographed or lifted using fingermark tape which is subsequently attached to clear acetate.
Ninhydrin is a chemical solution which is used to enhance fingermarks on porous surfaces such as paper and cardboard. The surface is washed with the solution and left to dry before being placed into a 70 degree Centigrade humid oven for 15 minutes. Ninhydrin reacts with the amino acids present in the fingermark deposit to produce a purple coloured mark. The fingermark is recorded using photography and appropriate camera filters.
Cyanoacrylate or super glue fuming is another technique which is used for non-porous surfaces. The vapour given off from the super glue reacts with some fingermarks. Items for enhancement are placed inside a specialist cabinet that controls humidity and allows super glue to vaporise. The vapour produces a white crystalline substance on the fingermark ridges. This also stabilises the mark. To further visualise the fingermark, it can be dyed using fluorescent dyes or powders can be applied.
Now we will look at some specific enhancement techniques in action!
These are very common chemical enhancement techniques used in a mark enhancement laboratory and make use of a variety of chemicals and methods of application. The choice of enhancement technique often depends on the nature of the surface and in particular whether it is porous or non-porous.
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