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What is the best method of lifting fingerprints?
Question Date: 2012-01-16
Answer 1:

There are several ways to lift fingerprints, depending on the nature of the chemicals contained in them.

Fingerprints left on a surface are known as latent fingerprints. These fingerprints contain mostly water, fatty acids, and triglycerides, with small amounts of amino acids and chlorides. In order to detect the fingerprint, we have to be able to detect one of these groups of chemicals. The general idea is to make the fingerprint easily visible and then photograph it as a means of preservation. It is usually easier to rely on a photograph than actually trying to preserve the fingerprint itself.

One way to make the fingerprint visible is to dust with a powder that will stick to the fingerprint and create contrast between the fingerprint and its background. The fingerprint can be photographed in place or lifted from the surface with lifting tape and placed on a contrasting surface. This technique works well on smooth surfaces.

Another way to make the fingerprints visible is to make them react with chemicals. For instance the amino acids in the fingerprint will react with ninhydrin or diazafluorenone. Ninhydrin turns blue or purple after the reaction so the fingerprints can easily be seen. When fingerprints treated with diazafluorenone are illuminated with blue light, they will glow yellow. There are many other methods for dying and staining fingerprints. Chemical developing methods like these are important because it allows for fingerprint detection on porous surfaces. It is usually difficult to detect fingerprints on these kinds of surfaces because the latent print can actually be absorbed into the material so dusting for prints does not work.

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