5.2: POWDERS

The first fingerprint powders were developed in the early 1920’s and used lampblack as a base. Lampblack is a finely powdered black soot deposited in incomplete combustion of carbonaceous materials, collected from fireplace chimneys or oil lamps, and used chiefly as a coloring agent in paints and inks. Since that time, fingerprints powders are made using resin, ferric oxide, lampblack, lead, mercury, cadmium copper, silicon titanium, and bismuth.

Powders are the old faithful partner of the fingerprint technician, and they can be used in the field and in the laboratory. Sometimes it is just the easiest solution to throw some powder. Fingerprint powders adhere to eccrine, apocrine, sebaceous oils, and contaminants. Most technicians in the field only use two colors of powder, black and silver, or bi-chromatic powders that have the unique quality of appearing black on light colored surfaces and silver on dark surfaces. White powders are good for developing fingerprints on dark surfaces. White powders photograph well but the developed prints are almost impossible to lift. Magnetic powders come in various colors and are great for developing prints on non-metallic surfaces. Application of magnetic powders is done with the use of a magnetic brush, which will be discussed in a later section of this chapter. Fluorescent powders have properties that allow the powder to fluoresce with the application of an Alternate Light Source, which will be explained in a subsequent chapter. They are incredibly bright and are useful on dark or multi-colored surfaces. Be forewarned, however, that a very tiny amount of fluorescent powder goes a very long way.

Figure \(\PageIndex{1}\): Fluorescent green fingerprint powder on a television screen - Author's collection

Brushes

There are two options for the application of regular fingerprint powders: ostrich feather or fiberglass brushes. Your author prefers an ostrich feather brush with a light, twirling touch, and a camel hair (or squirrel hair) brush for finishing. Fiberglass brushes are a bit less expensive than ostrich feather brushes, but they tend to get heavy with powder and there is less control, in your author’s opinion. Whatever technique or brush the technician finds that works best is fine, but practice, practice, practice. Be sure not to mix your brushes and to have one brush designated for each type of powder. Be careful of the surface you are using the brush on, and if the brush gets wet, throw it away.

Figure \(\PageIndex{2}\): Ostrich feather brush and regular black powder - Author's collection

Magnetic brushes are used to apply magnetic powders to non-metallic surfaces. They are very useful when the technician really does not want to make a tremendous mess, which will happen with regular powders. Also, magnetic powders can be used on porous surfaces because the powders are picked up by the action of the magnet and therefore do not smear the inks from the powder across the surface. The magnetic end of the brush will attract the magnetic powder to form a cluster of powder at the head. The powder can either be applied with the powder held in place by the magnet, or it can be retracted causing the powder to fall onto the area to be dusted. The powder is then pulled back to the magnetic head when the magnet is returned to its original position.

Figure \(\PageIndex{3}\): Magnetic brush and powder - Author's collection

Photographing and Lifting

Once a fingerprint is developed, it is essential to document the print using photography. The image must be photographed with the film plane at a 90-degree angle to the print to avoid distortion. There must be a scale in the image as well. Fingerprints developed with powders can be “lifted” from the surface of non-porous items using clear fingerprint tape or a hinge-lifter. Once the lift has been applied to a backing card, it is important to document the essential information relative to the crime being charged, and to document the direction of the lift using an arrow. It is also recommended that the technician provide a drawing of the item being fingerprinted with an arrow depicting the direction of fingerprint deposition. This card now becomes an item of evidence and must be treated as such.

Figure \(\PageIndex{4}\): Latent print developed on pill tin - Author's collection

Figure \(\PageIndex{5}\): Developing print being "lifted" with a hinge lifter. Fingerprint lifting tape is nearby. - Author's collection

Figure \(\PageIndex{6}\): The lifted developed fingerprint - Author's collection

Figure \(\PageIndex{7}\): Fingerprint backing card. Note the arrow depicting the direction of the lift. - Author's collection

Figure \(\PageIndex{8}\): Drawing of item being lifted with an arrow depicting the direction of the fingerprint. - Author's collection

To Lift or Swab

The dilemma faced by latent print technicians is always, is it better to develop a latent fingerprint impression or to swab the area for DNA. A developed fingerprint can be identified in a manner of minutes, whereas a DNA specimen might take months to get the results. Is it possible to do both? Yes, particularly in the laboratory following strict sterilization protocols of the equipment needed to process the item for latent prints. In the field, the technician can use sterile powders and brushes. These are single-use items that are manufactured and sterilized before being packaged in containers. The application devices are available either as single-use fiberglass brushes or sterile sheaths that are placed over magnetic brushes. Sterile powders are packaged and sold in small containers providing usually one ounce of powder. Other methods of sterile development will be discussed in the chemical section of this chapter.