Fingerprint powder is the “go-to” tool of all crime scene investigators in the detection and collection of latent prints left behind at crime scenes. Available in a variety of colors and material configurations, and specifically manufactured for the various investigative needs, each powder has features and benefits which should be considered for the individual crime scene. This guide provides an overview of the different types of fingerprint powders and the situations which dictate their use.
Early versions of fingerprint powders were generally handmade by latent print examiners or police crime scene technicians. In the early 1900’s, commercially-available powders were being produced, with some, most notably Lightning Powder® with its origin in 1936, still in business today.
Before the scientific advancement of latent print development, colors were limited to black and aluminum, with black being, by far, the powder of choice. Regardless of the surface color or type, black powder was used and prints developed. Generally, examiners used a very bright light to visualize the prints, especially on darker surfaces since the contrast was not there. The prints that developed were of exceptional quality; the only problem was that they just couldn’t be readily seen.
While black powder is still a staple, the convention today is to use a colored powder to provide a visual contrast to the surface being processed; dark surface – light powder, light surface – dark powder. Colors such as white, silver/gray (aluminum) or Bi-Chromatic™ are now used for almost any surface that may be encountered.
White powder works especially well on glass, chromed metals, plastic bags and dark colored surfaces. White powder generally consists of Titanium Oxide powder and an earth powder for base. The Titanium adheres well to the oils of the print and provides an excellent contrast to most surfaces it is used on, whether it is conventional or magnetic, or used on porous or non-porous surfaces.
Silver/Gray (aluminum) powder performs best on glass, plastic and rubber. The aluminum component of the powder adheres to prints on non-traditional surfaces and provides good contrast to the background surface.
Bi-Chromatic powders are typically a combination of black and aluminum powders, and were created to adapt to colored surfaces. When processing with Bi-Chromatic powder, any latent prints developed will be seen as black ridges on the light parts of the surface and light ridges on the dark part of the surface. Once these prints are lifted onto a white backing card, they will always appear as dark ridges.
Black powder is manufactured from a variety of carbon-based powders with a binder or earth powder added for stability. This staple of fingerprint powders readily adheres to the oily residues from the fingers and other body parts and is the most versatile of the fingerprint powders in that it can be applied to many surface types: porous and non-porous alike.
TYPES OF POWDERS
In addition to color, the physical composition of the powder should be selected depending on the characteristics of the crime scene. Powders can be defined as conventional (colorant and base), magnetic (colorant and iron shavings) and fluorescent (light stimulated colorant and base).
Conventional powders, applied with a fiber or hair brush, are the most common type of powders used at crime scenes. They are generally inexpensive, cover a large area when applied with a brush and readily develop prints on most non-porous surfaces. The main drawback is that conventional powders are generally very light and airy and can become airborne at the slightest flick of the brush, creating a mess.
Magnetic-based powders consist of colorants wrapped around iron filings. They are applied with the use of a magnet embedded inside a plastic or non-ferrous metal wand which attracts the filings and creates a clump or ball of powder. When the iron fillings are “rubbed” over the print surface, the colorant is deposited as it comes into contact with the oily residue. This process develops the image with little or no abrasive contact to the residue thus making magnetic-based powders ideal for more delicate type evidence. They are designed to work on some porous surfaces and non-porous surfaces like plastic, Styrofoam, rubber and the like.
Magnetic wands are useful in many situations, however, they are not ideal when processing prints upside down. The magnet does a fine job of managing the powder when the wand is held in a normal magnet-down position, but loses its effectiveness when used in a magnet-up position. Lastly, magnetic powder is easy to clean up simply by passing the wand over any filings left behind.
Fluorescent powders are used where a print is difficult to distinguish from its surface. Developed for use with any number of alternate light sources ranging from small 1-watt ultraviolet lights to multi-watt lasers, these powders work especially well on raw surfaces such as household woodwork, convenience store counters and multi-colored non-porous items where normal conventional powders may paint or clog the surface.
The colorants found in fluorescent powders are treated dyes which react to UV and purple/blue bands in the visible light spectrum, typical for crime scene work. The hues of the powders can be matched to the color of the surface processed and the wavelength of the light source being used. This coupling will help flatten or eliminate any background interference that may occur from the surface coloration or contaminants.
Spray powders are an evolution of fingerprint powder as a specialized tool to allow for specific spot processing. The measured portion of powder, delivered by a short blast from the can, provides enough powder to allow the development of prints without over-processing the background or the prints themselves. The spray powder is contained utilizing a containment tent to keep the powder in a confined space so it does not broadcast over other areas of the scene. The spray powder was designed to be an additional tool in the technician’s arsenal for certain situations and does not replace any of the powders mentioned above.
With a long and convincing history in crime scene processing, fingerprint powders have proven to be an essential tool in every crime scene and latent print examiner’s tool kit. Although black powder is the original and remains a popular choice, the scientific and technological advancements within the field are driving evolutions as diverse as the crime scenes themselves.
ABOUT THE EXPERT:
For more than 30 years, T. Allen Miller has been in the forensics industry. As the Forensics Product Manager for The Safariland Group for over 15 years, he has been responsible for the development and management of new products and educating customers on the application of forensic products across the country. Prior to joining The Safariland Group, Miller was a senior crime scene analyst for over 20 years at the Florida Department of Law Enforcement, Jacksonville Regional Crime Laboratory and provided crime scene processing services to more than 50 agencies in a 14 county area of Northeast Florida, including federal, state and local agencies.