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

develop it.



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

fingerprint camera.



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

when photographing.



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

tape.



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

white.



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

manner.



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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