Infra-red responsive fingerprint composition and method of making

An infra-red responsive fingerprint composition and method for manufacturing by sifting and mixing a minor proportion of finely divided carbon black (50 to 75 millimicrons) and a major proportion of infra-red responsive finely divided pigments containing milori blue (250 to 400 mesh), manganese dioxide (300 to 400 mesh), aluminum powder (1 to 75 microns) and mica (10 to 20 microns). A small amount of gum arabic as binder is included to facilitate adhesion of the print powder to latent prints. On white surfaces the fingerprint powder is black. On dark surfaces the fingerprint powder is brightly reflective so that when lifted or transferred to a white backing the color changes from brightly reflective to black. The reflective color becomes even more vivid under infra-red. Storage is preferably in tightly sealed containers in the presence of dessicant capsules to prevent moisture pick-up and caking of the gum arabic.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The invention relates to a novel fingerprint powder usable in the customary 
manner by sprinkling on latent prints, brushing off surplus and taking an 
impression by means of a tape, as well as by photographing. The invention 
further relates to methods of mixing the novel powder composition and to 
storing the composition under conditions where it can be used as 
affectively at a later time as when freshly made. 
2. Description of the Prior Art 
In Hedrick, U.S. Pat. No. 1,259,981, the standard black fingerprint powder 
is described as a combination of lamp black and gum adhesive and the use 
of the powder for taking prints is also taught employing the technique of 
spraying the print after dusting with an alcohol solvent to dissolve the 
gum. 
In White, U.S. Pat. No. 1,539,448, the use of a variety of differently 
colored print powders, each in its own container, is taught as an 
improvement for detecting latent prints left on a variety of surfaces. 
In Pitman, U.S. Pat. No. 1,951,203, the use of aluminum powder as a highly 
reflective component of the powder is disclosed. 
In Fonda, U.S. Pat. No. 2,447,322, iron compounds are disclosed at column 
2, line 5, as storage agents to retard the exhaustion of infra-red 
luminescence. At column 2, lines 35 et seq., manganese compounds are 
disclosed as activating agents for such storage. 
In Terek, U.S. Pat. No. 2,986,831, print powders based on lamp black or 
aluminum are used to make transfer prints or photographs. 
Similarly, in Bonora, U.S. Pat. No. 3,075,852, either carbon black or 
aluminum powder is used to make prints. 
Each of the above black fingerprint powders has the disadvantage of 
requiring a cumbersome variety of mixtures in containers and applicators 
and of further requiring a high degree of skill is using these multiple 
containers and applicators. 
OBJECTS OF THE INVENTION 
It is a primary object of the invention to provide a single fingerprint 
powder composition to replace the conventional carbon black pigment or 
aluminum pigment powders which is brighter and displays much higher 
contrast under reflected visible light and is further intensified in 
brightness and contrast under infra-red radiation to thereby improve the 
art of fingerprinting. 
It is a further object of the invention to provide improved fingerprint 
detection and recording by transfer and by photographing, under infra-red 
light, the print developed by dusting with the new fingerprint powder of 
the invention. 
SUMMARY OF THE INVENTION 
To accomplish the above objects, the novel fingerprint powder composition 
of the invention uses a combination of finely divided infra-red responsive 
pigments and visible light reflective pigments, the infra-red pigments 
including manganese dioxide and milori blue while the visible light 
reflective pigments include carbon black, mica and aluminum powders. A 
small but effective amount of adhesive, such as gum arabic, is added as a 
binder. Thorough mixing and sifting of the finely divided powders is 
carried out under by conditions and the thoroughly mixed product is stored 
in the presence of dessicant capsules to assure that caking will not occur 
during prolonged storage. 
Proportions, as identified blow, are critical: 
______________________________________ 
Range of 
Range of Par- 
Preferred Proportions 
Ingredient 
ticle Size Proportions By Weight 
______________________________________ 
Aluminum 1-75 microns 
17% 6-20% 
Carbon Black 
5-70 milli- 36% 30-48% 
microns 
Manganese 300-400 mesh 
18% 6-18% 
Dioxide 
Milori Blue 
250-400 mesh 
15% 6-18% 
Mica 10-20 microns 
12% 6-18% 
Gum Arabic 
USP Grade 3% 2-9% 
______________________________________ 
The particle size of each of the finely divided pigments set forth above is 
critical in order to achieve proper mixing in the dry state and to 
overcome the well known problems associated with carbon black fingerprint 
powders. The particle size of carbon black fingerprint powders using only 
gum arabic binder requires a very delicate balance between the properties 
of binder and carbon black which interferes with the use of the powder if 
it takes up moisture or is used under humid conditions. The black 
agglomerates and indistinct prints results because particles do not easily 
brush away. With the invention, all of the beneficial properties of the 
cabon black are retained with none of the faults mentioned above because 
each of manganese dioxide, milori blue, aluminum and mica is 
non-hygroscopic, non-agglomerating, highly reflective and intensely 
colored with separate spectral characteristics under visible and infra-red 
light. 
A unique coaction has been discovered between these aforementioned, 
non-carbon pigments, the gum binder and the carbon black to retain the 
print transfer capability of carbon black while adding unexpected 
characteristics of spectral reflectants to vividly outline latent prints 
based upon the non-carbon pigments. Manganese dioxide, an oxidizing agent, 
has a surprising effect on the enhancement of the print color under 
infra-red light which is unexpected. It is a stable, black tetravalent 
oxide of high hardness (6-6.5 Mohs scale) and high specific gravity (5.06) 
and would be expected to have no enhancement on infra-red phosphorescence 
or luminescence, when used in combination with milori blue. Milori blue is 
not used in phosphor compositions. Where manganese compounds have been 
used, as in Homer, U.S. Pat. No. 2,647,086, the compound is manganese 
carbonate used with cadmium phosphors and calcium phosphors. These are 
phorphors adversely affected by oxidation and obviously not suitable if 
the manganese carbonate was interchanged with manganese dioxide, an 
oxidizing agent. 
Milori blue is described at page 600, under iron blue, and at page 730, 
under milori blue, of Condensed Chemical Dictionary, Fifth Edition, 
Reinhold Publishing Company, 1956, as a commercial blue pigment having 
very dark intense mass tones and a green tint made by reacting a soluble 
ferrocyanide salt with iron sulphate thereby forming a ferrous 
ferrocyanide which is then oxidized to a ferric ferrocyanide. Kirk-Othmer, 
Encyclopedia of Chemical Technology, Second Edition, defines milori blue 
as a mixture of the ferric and ferrous salts which have the darkest and 
most intense tones of all of the manufactured blues and a characteristic 
green tint. It is the discovery of the properties of the black pigment 
effect of manganese dioxide and the green tint effect of milori blue that 
creates the new reflective results under visible and infra-red lights for 
the composition of the invention. 
Reflective aluminum and reflective mica introduce specular reflection into 
the mixture and contribute to the intensification of the visual or 
photographic image of the print. Thus, these function as miniature light 
reflectors.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
The following examples illustrate preferred compositions of the invention 
for use on differently colored surfaces: 
EXAMPLE 1 
Aluminum powder of 16 micron particle size was obtained as powder, grade 
number 1400, from Gold Leaf and Metallic Powders, Inc., Two Barclay 
Street, New York, New York 10017 and was mixed in an amount of 17 ounces 
with 36 ounces of carbon black, particle size 75 millimicons, in a five 
gallon drum, each of the two ingredients being passed through a sifter 
while being stirred by hand with a wooden spatula. This two component 
mixture was black in color despite the silvery appearance of the aluminum 
powder. To this mixture was added 18 ounces of 400 mesh manganese dioxide, 
technical grade, purchased from J. T. Baker Chemical Company, 222 Red 
School Lane, Phillipsburg, New Jersey 08865, 12 ounces of 10 to 20 micron 
powdered mica, purchased from English Mica Company, Kings Mountain, North 
Carolina, under grade number Micro-Mica 1000 and 15 ounces of 325 mesh 
milori blue, purchased from Mineral Pigments Corporation, 7011 Muirkirk 
Road, Beltsville, Maryland 20705. During the addition of the black 
manganese dioxide, milori blue and mica pigments there was simultaneously 
mixed 3 ounces of USP gum arabic which was in finely divided condition 
from the supplier, Amend Drug and Chemical Company, Irvington, New Jersey 
07111. 
After hand mixing for three to five minutes the drum was sealed, placed on 
a rotary mixer and mixed for an additional hour. The drum was then opened, 
inspected, hand-turned with the wooden spatula to verify mixing and then 
run through a sifter to remove any agglomerated particles. 
The sifted mixture was then stored with 1 to 2 dessicant capsules 
(anhydrous pressed silicon gel) in sealed 2, 4 and 8 ounce double-walled 
containers. 
EXAMPLE 2 
The same mixing procedure and the same proportions as in Example 1 were 
followed except that the amount of milori blue was changed from 15 ounces 
to 18 ounces and the amount of manganese dioxide was changed from 18 
ounces to 15 ounces. 
The product worked equally well as that of Example 1. 
EXAMPLE 3 
The same mixing procedure and same proportions were followed as in Example 
1 except that the amount of carbon black was reducd to 33 ounces instead 
of 36 ounces and the amount of milori blue was increased from 15 ounces to 
18 ounces. 
This product also worked equally well as that of Example 1. 
In each of the above examples, each ounce corresponds to about 1% by weight 
of the composition. 
Although each of the above examples provides excellent results which are 
far superior than those using the straight carbon black or multi-colored 
sets of finger prints powders, it is possible to vary, for each 
ingredient, the proportions as set forth under the Summary of the 
Invention. 
If aluminum is reduced to less than 6% by weight, the specular reflective 
benefit of aluminum is lost and the disadvantage of carbon black takes 
over. Although carbon black may be increased up to 48%, it is preferred 
that it represent about one-third of the composition. Less than 30% of 
carbon black results in a loss of contrast for print development. 
If manganese dioxide is used at a level less than 6%, the improvement of 
the surplus dust removal effect for the composition is lost. The optimum 
proportion at about 14 to 18% gives best balance for removal of surplus 
dust. 
If milori blue is used at less than 6%, the desirable green tint and the 
combined effect with manganese dioxide under infra-red is lost. The best 
color balance is between 15 to 18% for each of milori blue and manganese 
dioxide. 
Mica provides an entirely different effect than aluminum due to its 
lubricating properties and also due to a different type of reflection 
which is effective at greater than 6%. 
Gum arabic is preferably used at a minimum level, e.g., 2 to 3%. Larger 
amounts are less preferred because it adversely affects storage. More than 
9% cannot be used.