39 
can be made visible by appropriate treatment at any time 
within several hours after they are made, but the sooner 
the better. 
How to manipulate .—Sprinkle a powder of contrasting 
color on the surface containing prints. Distribute by 
tapping from a camel’s-hair brush or by patting with 
such a brush (not rubbing) or by agitation on the de¬ 
sired surface. Blow off the excess. Where the skin 
ridges touched the surface the powder will remain. Pow¬ 
ders used by police officers are aluminum (preferably 
10,000 fine) and bronze, one or the other of these forming 
sufficient contrast with almost any color. With expert 
manipulation these give the best results. Dragon’s blood 
powder for light surfaces and talcum powder or gray 
chalk for dark seem to work better, however, for those not 
expert in manipulation. All of them can usually be ob¬ 
tained at drug stores. When these are not available, 
powdered charcoal, or very fine pencil scrapings, answer 
for light surfaces; borax, even flour, for dark surfaces. 
All powders must be dry, since they pile up and work 
badly if damp. 
Prints thus developed are easily smudged by friction. 
They can be set by spraying lightly with a solution of one 
part white shellac (prepared floor shellac, not solid gum) 
in four parts wood alcohol. Dragon’s-blood powder, how¬ 
ever, can be set without the use of shellac by heating 
slightly with a match flame after application to the desired 
surface. 
On a large surface, when it is not known where the 
fingerprints may develop, they can be brought out in a 
brown color by heating the paper or other surface in a 
closed box with iodine crystals; the prints can then be 
recorded by one of the above powders, the iodine color 
vanishing after a time. 
Identification. —The pattern of the skin ridges is different 
for every individual, and for all 10 fingers of every indi¬ 
vidual. The lines fall into classes such as arches, loops, 
and whorls, which have been minutely classified for police 
records; but nothing is necessary for identification except 
a close examination and comparison, which anyone can 
