Discover: Fingerprint Collection

Scientists are able to lift fingerprints from almost any surface.  The most common method you might have seen shown on television involves the use of black fingerprint power on a flat surface.  Collecting fingerprints is an important step in gathering evidence, but it is not always as easy as it looks on television.  If the dusting for prints is not done correctly, likely the print could be destroyed in the process.

Fingerprints are classified into three categories based on the type of surface on which they are found and whether or not you can see the prints.

Fingerprints on soft surfaces (such as soap, wax, wet paint) can be made three-dimensional plastic prints.

Fingerprints on hard surfaces can be either patent/visible or latent/invisible.

Visible prints are formed when blood, dirt, ink, paint is transferred from a finger or thumb to a surface such as paper, cloth, wood, metal, glass, or plastic. These can be photographed.

Latent fingerprints are marks left by oil and sweat that you are not able to see (invisible).  Latent prints are left on any surface that you touch, but they require special techniques such as powder, light, or chemicals to be seen.

Fingerprint powder is of different colours.  The colour of powder used depends on the colour of the surface.  A colour contrast is created so the fingerprint will be seen. A light-coloured powder works well on a black surface and a dark coloured powder works well on a white surface.

Fingerprint powders and chemicals can contaminate the evidence and destroy additional information.

Therefore, investigators use more modern fingerprinting techniques such as alternate light sources such as laser or LED devices. A blue light with an orange filter for example will allow investigators to take a picture of a latent fingerprint on a doorway, windowsill, or railing. Another modern technique is using superglue fumes which stick to an object and allow latent fingerprints to be seen under white light.

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