United States Patent (19) 11 4,260,645 Kerr et al. 45) Apr. 7, 1981

LATENT FINGER PRINT DETECTION 54 OTHER PUBLICATIONS 75 Inventors: F. Michael Kerr, Ottawa; Alan D. Sharp, D. W. A. et al., J. Chem. Soc., Part II, pp. Westland, Chelsea, both of Canada 1855-1858 (1956). 73 Assignee: Canadian Patents and Development C.A., vol. 63,9729d (1965). Limited, Ottawa, Canada C.A., vol. 48, 13520d (1954). 21 Appl. No.: 508 C.A., vol. 61, 6894g (1964). C.A., vol. 48,5704i (1954). 22 Fied: Jan. 2, 1979 C.A., vol. 53, 6866a (1959). 51 int. Cl...... B41M 5/00; C09K 3/30; C.A., vol. 48, 3080i (1954). C09K 3/00; G01N 33/16 Primary Examiner-Teddy S. Gron 52 U.S. C...... 427/1; 106/19; 106/21; 118/31.5; 252/182; 252/408; 422/61 Attorney, Agent, or Firm-Alan A. Thomson 58) Field of Search ...... 106/19, 21; 252/182, 57 ABSTRACT 252/408; 422/61; 118/31.5; 427/1 Latent fingerprints can be detected and visualized by 56) References Cited application to the suspected locale, of a solution, in a U.S. PATENT DOCUMENTS volatile organic solvent of selected salts soluble in said solvent. Suitable salts include silver 2,235,632 3/1941 Heinecke ...... 106/21 3,075,852 1/1963 Bonora ...... 8/31.5 and silver trifluoroacetate. The solution is preferably 3,148,277 9/1964 Lewanda .. ... 8/31.5 applied as a spray. This non-aqueous solution minimizes 4,182,261 / 1980 Smith et al...... 106/2: Smudging, "running', warping and other damage to water-sensitive material (usually inks, dyes and/or cel FOREIGN PATENT DOCUMENTS lulosic substrates). 1428025 3/1976 United Kingdom...... 18/31.5 1497791 1/1978 United Kingdom ...... 427/1. 11 Claims, No Drawings 4,260,645 1. 2 (a) a volatile organic solvent, and LATENT FENGERPRINT DETECTION (b) a silver salt soluble in said solvent, sufficient silver ions being present to visualize a latent print, This invention is directed to the detection of, and (ii) evaporating the solvent, allowing reaction of sil visualization of latent fingerprints on various substrates ver ion with fingerprint material to proceed and photo particularly substrates which are susceptible to damage actinic effects to occur leading to visualization of the by aqueous systems. A non-aqueous organic solution is fingerprint, and provided containing silver ions which are able to react (iii) preserving or recording the fingerprint outline. with and become preferentially deposited on, the finger The components may be packaged separately as a kit print residual material. The solution is adapted to be O comprising sprayed onto the suspected substrate or fingerprint lo (a) organic solvent-soluble silver salt, cale with a propellant or by other suitable spray means. (b) volatile organic solvent for the salt; and DESCRIPTION OF PRIOR ART (c) means to spray or propel the solution onto a sub Strate. Current techniques for fingerprint detection utilize 15 reagents which interact with one or more of the compo DETALED DESCRIPTION nents in the fingerprint. The most commonly utilized The volatile organic solvent serving as carrier for the print components and reagents (especially for cellulosic silver ions, is chosen for its ability to dissolve silver substrates) are: salts, to readily evaporate, relative inertness with re (i) Amino-acid-sensitive reagents, particularly ninhy 20 spect to inks, dyes and cellulosic substrates, and low drin in various carriers. Some substrates such as coated toxicity and flammability. The hydrocarbon solvents, or papers (banknotes, documents etc.), rag-based papers, and some textiles are ninhydrin-positive, giving a back hydrocarbon components in the case of solvent mix ground reaction and inadequate contrast in many cases. tures, will necessarily have unsaturation present. Vola Depending on the carrier and the substrate, other limi 25 tile organic solvents which have been found to be the tations can be: low sensitivity, uncontrollable develop most suitable for our purpose include aromatics such as ment time, ink- or dye-"running', and high flammabil , and unsaturated aliphatics such as 1-hexene. ity. They dissolve the selected silver salts to a substantial (ii) Chloride-sensitive reagents, particularly aqueous concentration (saturation is usually about 4 to 6%) and solutions. This reagent reacts with the 30 do not seriously "run' or smear most inks or dyes nor chlorides present in fingerprints to produce the highly distort most cellulosic substrates. Appropriate organic insoluble and light-sensitive . The white solvents include benzene, , xylene or mixed xy silver chloride decomposes actinically to deposit silver lenes, 1-hexene, and mixtures of methanol or ethanol and give a black image of the latent print. Defects of this with unsaturated aliphatics such as cyclohexene (stabi reagent include severe ink-"running', and high back 35 lized with sodium hydroxide as supplied commercially). ground reaction in some cases, leading to overall dark In the latter mixture, about 5 to about 50% by vol. ening of the whole substrate area. (iii) Fat-sensitive would be the cyclohexene or equivalent. This latter reagents, primarily iodine vapour or the recently re mixture is not to be used with silver perchlorate but ported osmium tetroxide (see RCMP Gazette, Vol. 40, may be used, e.g. with the fluoro salts. The toxicity and No. 3, 1978, page 28). An iodine source, e.g., iodine flammability of these solvents is acceptably low. The fuming pipe or iodine-saturated silica gel or iodine alcohol-containing solvent is preferred for low toxicity; loaded porous glass, is used to expose the latent print however it can lead to some smearing of ballpoint pen area to iodine vapour and usually a silver plate is then inks. Cyclohexene alone and 1-hexene are next in order pressed against the surface containing the iodine of preference for toxicity. Water-base inks and ballpoint saturated print residue, the exposed plate then being 45 inks are both stable to these solvents. Another solvent developed to reveal the image. These methods have which may be used is acetonitrile although this has some manipulative and toxicity difficulties so that pre increased smell and toxicity. Some unsaturation in at cautions and careful handling are required. least one component of a hydrocarbon-containing sol It would be desirable to have improved print-sensi vent has been found necessary. Mixtures of solvents can tive reagents which avoid at least some of the above 50 be used. difficulties. An improved chloride-sensitive reagent The selected silver salts are limited primarily by solu which avoids the ink-"running' problem and has mini bility, but stability, cost, availability, safety and other mal background reaction would be particularly desir factors enter in. The silver salts most suitable include able. silver perchlorate, and fluoro salts such as silver hexa 55 fluorophosphate, silver hexafluoroantimonate, silver SUMMARY OF THE INVENTION tetrafluoroborate and silver trifluoroacetate. In general, We have developed a chloride-sensitive non-aqueous any silver salt soluble in organic solvents to at least solution suitable for application to latent fingerprints for about 0.5% by weight would be operative. Mixtures of detection and visualization thereof, comprising two or more of these salts can be used. (a) a volatile organic solvent, and The concentration of silver salt in the organic solvent (b) a silver salt soluble in solvent (a), sufficient silver can range from about 0.5% by weight up to saturation. ions being present to visualize a latent print in one Desirably sufficient silver salt is present in the solution spray application. so that one spray application will deposit enough silver The invention includes a method for detection and to visualize the print. From about 1 to 3% by weight is visualization of latent fingerprints where the use of 65 usually suitable, preferably about 3%. These solutions aqueous media is detrimental, comprising are reasonably stable and have been stored for up to 3 (i) uniformly contacting the latent print area with a months or more without significant deterioration. The non-aqueous solution comprising solutions should not be stored in contact with most 4,260,645 3 4. metals since many metals can lead to deterioration by enough to make fingerprint detection in the vicinity of deposition of silver. the writing very difficult. These organic solutions are coated on the fingerprint As well as the above toluene-based spray other salt substrate or suspected locale in any convenient man solvent combinations have given good results as sum ner-usually by spraying. Mechanical spray means can marized in Table 1. be used or the solution can be contained under pressure with a propellant. Any of the standard propellants may TABLE SUMMARY OF FINGERPRINT RESULTS be used such as compressed air, fluorinated or chloro USING WARIOUS SILVER SALTS AND fluoro-hydrocarbons (e.g. a Freon (trademark) type), VARIOUS VOLATILE ORGANIC SOLVENTS CO2 gas, nitrous oxide or N2 gas, or a highly volatile 10 TOX- OTHER hydrocarbon (methane to butane). The latter are flam ORGANIC CITY OF COM mable and their use requires caution. Aerosol spray SILVER SALTS SOLVENT SOLVENT MENTS containers may be used as long as any metal is coated or 1. Silver Perchlorate Benzene High b not in direct contact with the solution. AgClO4. 15 2. Silver Perchlorate Toluene Moderate b A packaged unit or kit can be provided for conve AgClO4 nience, comprising interacting components 3. Silver Perchlorate Xylene or b (a) the organic solvent-soluble silver salt, AgClO4. Mixed Xylenes 4. Silver Perchlorate 1-Hexene FP b (b) the volatile organic solvent for (a) and AgClO4 (c) means to spray or propel the solution. 5, Silver Nitrate Cyclohexene- C The substrates for which these silver salt-organic 20 AgNO3 Alkanol 6. Silver Tetrafluor- Benzene High b solvent solutions are particularly suitable include paper oborate AgBF4 and other cellulosics, some textiles and water-sensitive 7. Silver Tetrafluor- Toluene and Moderate b materials or coatings in general. oborate AgBF4 Xylenes The application of heat speeds up the reaction of 2 8. Silver Nitrate Acetonitrile High c,d silver with the print composition and additional light a 5 AgNO3 accelerates the decomposition and deposition of sil 9. Silver Hexafluoro- Acetonitrile WF c,d ver-leading to more rapid development rates if de antimonate AgSbF6 Concentration of solution is 3% by weight unless otherwise indicated. sired. However, room temperatures and normal room b. No smearing of ballpoint ink; no distortion of paper light or outdoor daylight are adequate in most cases. c Smearing of ballpoint inks less severe than with aqueous sprays The developed print of the fingerprint is usually re 30 d Concentration less than 2% by weight due to limited solubility corded photographically and the film stored. 5-50% by volume of cyclohexene with methanol or ethanol The following Examples are illustrative. We claim: EXAMPLE 1. 1. A method for detection and visualization of latent 35 fingerprints where the use of aqueous media is detri Pure white relatively porous bond paper containing mental, comprising fountain pen writing was used as the substrate. A 3% (i) uniformly contacting the latent print area of the silver perchlorate in toluene solution was sprayed on substrate with a non-aqueous solution comprising the paper and time allowed for solvent evaporation, (a) a volatile organic solvent with unsaturation pres reaction and development at room temperature in nor ent, and mal room light. The fountain pen writing was un (b) a silver salt soluble in said solvent, sufficient silver changed. Several fingerprints were seen to show up ions being present to visualize a latent print, the clearly with good contrast. silver salt being selected from silver perchlorate, When the same paper with fountain pen writing was silver hexafluoroantimonate, silver hexafluoro sprayed with standard aqueous silver nitrate, the writ 45 phosphate, , silver trifluor ing became smeared and blurred with parts of the writ oacetate, and mixtures thereof; ing becoming illegible. (ii) evaporating the solvent, allowing reaction of sil ver ion with fingerprint material to proceed and EXAMPLE 2 photo-actinic effects to occur leading to visualiza Bank cheques on special safety paper and having 50 tion of the fingerprint, and three written signatures thereon were tested using the (iii) preserving or recording the fingerprint outline. same sprays as in Example 1. With the toluene-silver 2. The method of claim 1 wherein the solution is perchlorate spray the cheques were substantially unal sprayed over the entire latent print area. tered. However, with aqueous silver nitrate spray the 3. The method of claim 1 wherein the solvent is se signatures and written dates became very blurred and 55 lected from benzene, toluene, xylene, mixed xylenes, there was some evidence of ink migration to other parts 1-hexene, cyclohexene, and mixtures thereof. of the cheques. With the toluene-based spray finger 4. The method of claim 1 wherein the fingerprint prints could be readily visualized without interference outline is recorded photographically. from migrated ink. 5. The method of claim 1 wherein the solvent is tolu EXAMPLE 3 60 ene, the salt is silver perchlorate and the salt concentra tion 1-3% American Express travellers' cheques were tested as 6. A kit for the detection and visualization of latent substrates using the same sprays as in Example 1. With fingerprints comprising the toluene-based spray there was only very slight dam (a) a silver salt selected from silver perchlorate, silver age (signatures and dates still legible but slight ink mi 65 hexafluoroantimonate, silver hexafluorophosphate, gration). However, with the aqueous spray the written silver tetrafluoroborate, silver trifluoroacetate and signatures became substantially illegible with extensive mixtures thereof, ink migration occurring. This ink migration was serious (b) volatile unsaturated organic solvent for (a), and 4,260,645 5 6 (c) mechanical means to spray or propel the solution suitable for application to latent fingerprints for detec of (a) plus (b) onto a substrate. tion and visualization thereof, said solution comprising: 7. The kit of claim 6 wherein the salt and solvent are (a) a volatile organic solvent with unsaturation pres packaged in the form of a solution. ent; and 8. A non-aqueous solution suitable for application to (b) a silver salt soluble in solvent (a) and selected latent fingerprints for detection and visualization from the group consisting of silver perchlorate, thereof, comprising: silver hexafluorophosphate, silver hexafluoroanti (a) a volatile solvent mixture of an alkanol selected monate, silver tetrafluoroborate, silver trifluor from methanol or ethanol, and from about 5 to oacetate and mixtures thereof. about 50% by volume of the mixture of cyclohex 10 ane; and 10. The solution-propellant combination of claim 9 (b) a silver salt selected from the group consisting of wherein the propellant is selected from volatile haloge silver hexafluorophosphate, silver hexafluoroanti nated hydrocarbons, inert gases, and highly volatile monate, silver tetrafluoroborate, silver trifluor hydrocarbons. oacetate and silver nitrate; the silver salt being 15 11. The solution-propellant combination of claim 9 present in from about 1 to about 3% by wt. wherein the volatile organic solvent is selected from 9. A sprayable non-aqueous solution dispersed in an benzene, toluene, xylenes, cyclohexene, and 1-hexene. aerosol propellant under pressure, the solution being s se k

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