Technical Note

Latent Print Powders

How and When to Dust with Regular Powders

For many crime scene investigators, more than half of the powder used is regular, nonmagnetic powder. It can be used on windows, counter-tops, television sets and many other items moved or touched at residential burglary scenes. At commercial burglary scenes, it can be used on metal file cabinets, painted doors, broken glass and metal window frames. Regular powders can be applied to the painted surfaces, glass windows and mirrors in recovered stolen vehicles. At most of the day-to-day crime scenes visited, the crime scene investigator will have the opportunity to use regular powder on many surfaces. Regular powders are available in colors such as black, silver/gray, Bichromatic™ and white. Choose a color which will provide sufficient contrast with the background surface to obtain a clear photograph of the latent print. Black is one of the most popular colors used because once the latent print is lifted and placed on a backing card, the ridges of the latent print will be black against the white backing card. This makes it easy for the latent print examiner to compare the black ridges of the latent print to the black ridges of the inked print.

However, to be able to photograph the latent print against a dark-colored background, silver/gray powder can be used. It will be necessary to place it on a black backing card when it is lifted. For some latent print examiners, this can cause difficulties having to compare the light colored ridges of the latent print to the dark colored ridges of the inked print. There is also the necessity of having to carry two jars of powder, two brushes and two sets of backing cards. To solve this problem, many crime scene technicians use Bichromatic™ latent print powder.

Bichromatic™ latent print powder is a combination of black and silver/gray powder which can be dusted on a light or dark surface. On a light-colored surface, the latent print will appear dark so it can be seen and photographed easily. On a dark-colored surface, it will appear light. When lifted with tape and placed on a white backing card, the latent print will appear dark. This solves the problem for all involved. The crime scene investigator only has to carry one powder, one brush and one color of backing cards. The latent prints will be visible on a light or dark colored surface and the latent print examiner only has to compare the dark ridges of the latent print to the dark ridges of the inked print.

Now that a color has been chosen, decide upon the method of application. Regular powders are applied with brushes. Materials used to make brushes include camelhair, squirrelhair and fiberglass. Most crime scene investigators prefer a fiberglass brush, such as the Zephyr® Fiberglass Brush, because it is easy to use, the powder can be applied quickly and the chances of damaging the latent print are fewer. Some crime scene investigators learned with camelhair brushes and that is all they want to use. Others learned with a fiberglass brush and nothing will convince them to switch to a camel- or squirrelhair brush.

Regardless of which brush is used, the technique of the crime scene investigator is very important. Just as one investigator can get excellent results with a fiberglass brush because of proper training and sufficient practice, another investigator will get poor results because of lack of training and insufficient practice. Here are a few helpful hints in dealing with latent print powder. Keep the powder dry so that moisture does not cause it to become lumpy or hard. If the powder does turn into a solid lump, shake the jar (with the lid on) to break it loose. If necessary, place a couple of ball bearings in the jar to keep the powder loose.

While the brush can be dipped directly into the jar of powder, it is better to construct a small tray out of thin cardboard, such as an 8" x 8" fingerprint card. A small portion of powder can be poured into this small tray to facilitate loading the brush with powder. Others do not feel that this is necessary and load the brush with powder by dipping it into the jar. It is easy to get too much powder on the brush this way or to knock over the jar of powder. If you do decide to load your brush directly from the jar, keep the jar half full. This leaves room to move the brush around inside the jar to knock off the excess powder.

When applying powder to a surface, start with a light touch. It is easy to add more powder, if necessary, but it can be difficult to take away excess powder. Use the brush with gentle, light strokes. Latent print residue can easily be wiped away with too heavy of a stroke.

How and When to Dust with Magnetic Powders

When dusting with magnetic powders, it is necessary to use a magnetic powder applicator. The applicator has a magnet in the end to pick up and hold the magnetic powder in the shape of a fuzzy ball. Apply the powder by lightly "brushing" it over the surface of the evidence. Do not let the tip of the applicator touch the surface. Only the ball of powder should touch the surface. If the tip of the applicator should touch the surface, it may wipe away or mark the latent print.

When you have finished dusting the surface, hold the magnetic applicator over the open jar of powder and pull up on the knob at the opposite end of the applicator. This draws up the magnet away from the end with the powder on it and the powder will fall loose into the jar. Any powder which falls off of the surface or misses the jar can be picked up with the magnetic applicator and put back into the jar. Magnetic powder is economical, as very little is wasted.

How to Lift a Latent Print After Dusting

Latent prints developed with either type of powder can generally be lifted with adhesive tape, such as rolls of frosted or clear tape, poly tape or Handi-Lifts™ and Lightning Lifts™ pre-cut tape strips. The process is simple. After the latent print has been developed with powder, press a piece of tape on the surface and rub it to make sure complete contact is made. Be sure that the size of the piece of tape is large enough to cover the latent print.

Remove the piece of tape from the surface and press it onto a latent print backing card. Use a white backing card for latent prints developed with black or Bichromatic™ powders. Use a black backing card for latent prints developed with silver/gray or white powders. Handi-Lifts™ are available with a white, black or transparent backer attached to them.

It is important to make notations on the backing card to indicate from where the latent print was recovered. Preprinted backing cards have boxes to fill in for the date, time, case number and other information regarding the latent print lifted. It is suggested that you write your initials half on the lift tape and half on the backing card. This shows you have put the tape on the backing card and no one else tampered with it or put another piece of tape with another latent print on it on your backing card.

Another method to provide a chain of custody record is to use numbered backing cards. You would use a series of numbered backing cards at a crime scene. These numbers would be noted in your crime scene report. If any backing cards with the wrong number or no numbers appear in the group of backing cards with the case evidence, it may be a fabricated piece of evidence.

This has been a brief explanation of how to develop latent prints using regular and magnetic powders. There are many other methods for developing latent prints, such as fluorescent powders and dyes and other chemicals for developing latent prints on special surfaces. Other Technical Notes are available for these more advanced methods.

© 1996 Lightning Powder Company, Inc., Salem, Oregon, USA
Prepared by Kathleen D. Saviers, CLPE, CSCSA

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