Mechanical Operation

In order to take good fingerprints, the necessary equipment should be

maintained in a neat and orderly manner at all times.



Poor impressions are usually caused by one of the following faults:



1. The use of poor, thin, or colored ink, resulting in impressions

which are too light and faint, or in which the ink has run,

obliterating the ridges. The best results will be obtained by using

heavy b ack printer's ink, a paste which should not be thinned before

using. This ink will dry quickly and will not blur or smear with

handling.



2. Failure to clean thoroughly the inking apparatus and the fingers of

foreign substances and perspiration, causing the appearance of false

markings and the disappearance of characteristics. Windshield cleaner,

gasoline, benzine, and alcohol are good cleansing agents, but any

fluid may be used. In warm weather each finger should be wiped dry of

perspiration before printing.



3. Failure to roll the fingers fully from one side to the other and to

ink the whole area from tip to below the first fissure. The result of

this is that the focal points of the impressions (the deltas or cores)

do not appear. The whole finger surface from joint to tip and from

side to side should appear.



4. The use of too much ink, obliterating or obscuring the ridges. If

printer's ink is used, just a touch of the tube end to the inking

plate will suffice for several sets of prints. It should be spread to

a thin, even film by rolling.



5. Insufficient ink, resulting in ridges too light and faint to be

counted or traced.



6. Allowing the fingers to slip or twist, resulting in smears, blurs,

and false-appearing patterns. The fingers should be held lightly

without too much pressure. The subject should be warned not to try to

help but to remain passive.



The illustrations numbered 366 through 377 show the results of these

faults and show also the same fingers taken in the proper manner.