By: Don Penven, Tech Support
Latent print powders come in five different formulations:
Regular-Oxide, Metallic, Magnetic, Combination and Fluorescent. This article covers the basic theory of each type. Keep in mind that if you are uncertain which powder to use on a particular surface—experiment by placing your print in an area not likely to have been touched by the perpetrator.
These powders are considered the basic choice by crime scene investigators for use on many of the surfaces encountered at crime scenes. But many practitioners are not aware of some of the limitations. Examples of regular-oxides are: black, white, gray and red. These finely milled powders are highly sensitive toward the moisture or oily content of latent fingerprints. But their use should be limited to just non-porous surfaces such as most painted metals, plastics, waxed surfaces, glass, rubber, leather and wood (painted and unpainted). They should not be used on highly polished surfaces such as chrome or silver plating or other polished metals. Regular-oxide powders are applied with a brush. A powder color is selected based on how much contrast from the background it affords. Use black powder on light-colored surfaces and white powder on dark colored surfaces. Gray and red powders are often used on either light or dark surfaces.
As the name suggests, these powders are formulated from metallic substances such as aluminum, copper and zinc. They are specifically formulated for use on highly polished surfaces like chrome or silver plating. Using a regular-oxide powder on this type of surface generally results in the moisture residue from latent prints being damaged or destroyed—these ridge structures are simply wiped away. Metallic powders are applied with a brush.
Magnetic powders are formulated from iron or iron oxide. The powders themselves are not magnetic, but they are easily magnetized by a magnetic wand. Magnetic powders may be used on virtually any surface EXCEPT a surface containing iron or steel. The principle of delivery is this: a magnetic wand is passed over the powder, which is then attracted to the wand to form a “brush” made of the powder. The CSI then passes this powder brush over the surface so that the tip of the wand does not touch the surface, but the powder does. When carefully applied, magnetic powders leave very little surface residue so cleanup is simplified. Magnetic powders are available in black, gray and white for contrast with the surface.
These powders combine the properties and chemistry of both regular-oxide powders and metallic powders. The benefits here are:
- Combination powders may be used on virtually ANY non-porous surface
- These powders appear dark on a light background and light on a dark background.
Combination powders are applied with a brush.
Note: fluorescent powders use a formulation similar to regular-oxide powders and are thus best suited to work on those surfaces mentioned above.
Fluorescent powders appeared in the crime scene kits of CSIs who wanted a powder that was usable on multi-colored, confused backgrounds like soda cans, snack wrappers and bags, wallpaper, ceramic surfaces, etc. These powders contain a chemical that produces fluorescence when exposed to ultraviolet (UV) light or certain frequencies from alternate light sources (blue, yellow, green and red). When developed latent prints are viewed under subdued ambient light the fluorescence is bright enough that when the prints are photographed, the background is mostly dropped out. Fluorescent powders are applied with a brush.
For more information on latent print development using powders, chemicals and fuming techniques, download the Latent Print Development section of our catalog and read over pages 9-12. Latent Print Development
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