Lifting Fingerprints

There are several techniques for lifting a fingerprint from a surface. These include fingerprint powders, iodine fuming, and silver nitrate.

Fingerprint Powders

Powders - such as talc or even baking soda - can be dusted lightly onto a fingerprint. If you remove the excess by lightly puffing on the print or tapping at it with a brush, the fingerprint will be revealed and then you can place the print on a piece of tape, which will then be put on a contrasting sheet of paper for viewing.

Iodine Fuming

Also used to show invisible fingerprints is iodine fuming. The print will be placed inside of a small container filled with iodine crystals. When the container is heated, the iodine will convert to vapor and react with traces of the print left behind that will show an easily seen print. The fumes will wear off quickly and the print will fade, so a quick picture is necessary.

Silver Nitrate

When used with fingerprints, silver nitrate reacts with the salt in sweat left behind by the finger, which then transforms into silver chloride. If viewed under ultraviolet light, the print will appear and be a rusty color.

Types of surfaces:

• Porous
• Paper, cardboard, unfinished wood - prints are easily preserved because they soak into the material.
• Hard Surface
• Asphalt, cement - prints are not easily preserved because the surface is bumpy and prints are often disfigured and distorted
• Smooth Surface
• Glass, finished wood, plastic - prints can be easily lifted from smooth surfaces