Articles from The Science Of Fingerprints
The Classification Formula
Radial And Ulnar Loops
The Tented Arch
Preparation Of Fingerprint Charts For Court Testimony
Classification Of Bandaged Or Imprinted Fingers
Powdering And Lifting Latent Impressions
The sole purpose in developing a latent impression is to make it
visible so that it may be preserved and compared. Various powders and
chemicals are used for this purpose. When a latent print is plainly
visible, it should be photographed before any effort is made to
No attempt should be made to brush or apply powder to prints in dust,
obviously greasy prints, or bloody prints, as this will almost surely
destroy them. Objects which have been wet or immersed in water may
still bear identifiable latent impressions. Before any examination is
attempted, however, the object must be dried.
Powder brushed lightly over a latent-bearing surface will cling to
grease or moisture in the ridges of a latent print, making it visible
against the background. Obviously, a powder should be used which will
contrast with the color of the surface. Photographic contrasts should
also be considered.
A gray powder and a black powder are adequate for latent print work.
Many fingerprint powders of various colors and compositions are
available from fingerprint supply houses but none are superior to the
gray and black.
A very small amount of powder is placed on the brush for application
to the surface. Once the contour of a print is visible, the brush
strokes should conform to the direction of the ridges. All excess
powder should be brushed from between the ridges. Too much powder and
too little brushing are the chief faults of beginners.
Gray powder is used on dark-colored surfaces. It is also used on
mirrors and metal surfaces which have been polished to a mirrorlike
finish, since these surfaces will photograph black with the
Black powder should be applied to white or light-colored surfaces.
Aluminum powder affords the same contrast as the gray. Gold and red
bronze powders, although of a glittering appearance, will photograph
dark and should consequently be used on light-colored surfaces.
Dragon's blood powder is a photographically neutral powder and may be
dusted on either a light or dark surface.
On clear transparent glass, either gray or black powder may be used,
it being necessary only to use a contrasting black or white background
Prints should be lifted after photographing. Both rubber and
transparent tape are available for this purpose. Rubber lifting tape
is procurable in black or white 4 x 9 sheets and has the adhesive
surface protected with a celluloid cover. A black powder print should
obviously be lifted on white tape and a gray powder print on black
Gold bronze and red bronze powders should be lifted on white tape,
aluminum on black. Dragon's blood may be lifted on either black or
After cutting a piece of tape sufficiently large to cover the entire
latent print, the celluloid covering is removed and the adhesive side
applied to the latent. The tape should be pressed evenly and firmly to
the surface, taking care not to shift its position. It is then peeled
gently from the surface and the piece of celluloid placed over the
print to protect it. The operator should handle the lift in such a
manner that he will leave no prints of his own on the adhesive
surface. A small paper identification tag bearing the initials of the
operator, date, and object from which lifted should be placed under
one corner of the celluloid, or this information may be written on the
back of the lift itself if it can be done in a permanent, legible
If an excessive amount of powder adheres to the latent print, a more
legible print may sometimes be obtained by lifting a second time (on a
new piece of tape, of course).
It should be noted that a print lifted on rubber tape is in a reverse
position. Consequently, in preparing a photograph of a print on such a
lift, it will be necessary to print the negative from the reverse side
in order for the print to appear in its correct position for
comparison. Preparation of such photographs should not be attempted by
persons of inadequate knowledge and experience.
Transparent tape with a durable adhesive surface is available in 1 to
2 widths for fingerprint work. The common variety of transparent tape
is not suitable due to the deterioration (drying) of the adhesive
surface. The print on a piece of transparent tape is in correct
position. Transparent lifts should be affixed to a smooth, grainless,
opaque background of a black or white color contrasting with the
powder used. Every effort should be made to avoid air bubbles under
such lifts. In no instance should a transparent lift ever be folded
back on itself or stuck to another piece of such tape as a backing,
since it is generally not possible to determine the correct position
of such a print.
Groups of latent impressions, such as those of adjacent fingers or
fingers and palms which appear to have been made simultaneously,
should be lifted as units, that is, on a single piece of tape, as this
may facilitate the task of making comparisons.
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