NCJ Number
46067
Journal
Police Research Bulletin Issue: 30 Dated: (SPRING 1978) Pages: 16-23
Date Published
1978
Length
7 pages
Annotation
METAL DEPOSITION IN A VACUUM, AN INDUSTRIAL PROCESS USED TO COAT HEADLAMP REFLECTORS AND PRODUCE ELECTRONIC COMPONENTS, IS DESCRIBED AS AN EFFECTIVE TOOL FOR DEVELOPING FINGERPRINTS ON PAPER AND FABRICS.
Abstract
THE PRESENT 'STATE OF THE ART' IN FINGERPRINT DEVELOPMENT BY METAL DEPOSITION, A TECHNIQUE DEVELOPED IN ENGLAND, IS SUMMARIZED. TYPICAL APPARATUS FOR THIS WORK IS A GLASS VACUUM VESSEL WHICH IS EXHAUSTED BY A STANDARD PUMPING SYSTEM. SATISFACTORY PRESSURE CAN BE OBTAINED IN ABOUT SEVEN MINUTES. THE METAL, USUALLY A COMBINATION OF GOLD, THEN CADMIUM, IS EVAPORATED FROM OPEN CONTAINERS AT THE BASE OF THE CHAMBER BY ELECTRICAL HEATING AND THE DEPOSITION RATE AND FILM THICKNESS ARE MONITORED BY A QUARTZ CRYSTAL MONITORING SYSTEM. OTHER METAL COMBINATIONS HAVE BEEN STUDIED, BUT SENSITIZATION WITH A THIN LAYER OF GOLD, FOLLOWED BY A 'DEVELOPING' LAYER OF CADMIUM, WORKS BEST. PRELIMINARY EXPERIMENTS INDICATED THAT THIS METHOD WAS MORE EFFECTIVE THAN POWDERS FOR DEVELOPING FINGERPRINTS ON POLYTHENE. FINGERPRINTS STORED INDOORS FOR ONE MONTH COULD BE DEVELOPED WITH SUCCESS RATES BETWEEN 50 PERCENT AND 75 PERCENT. FINGERMARKS LEFT OUTDOORS BUT SHELTERED FROM THE RAIN HAD A SIMILAR SUCCESS RATE. OPERATIONAL TRIALS USING ACTUAL CRIME EVIDENCE DEVELOPED FINGERPRINTS IN OVER 50 PERCENT OF CASES. ENGLAND THEN MADE THE PROCESS AVAILABLE TO METROPOLITAN POLICE AND PROVINCIAL POLICE FORCES FOR USE ON POLYTHENE ARTICLES (1975). SINCE THEN AN OPERATIONAL TRIAL HAS CONFIRMED THE SUCCESS OF THIS METHOD IN DEVELOPING FINGERPRINTS ON BANK NOTES; THE SUCCESS RATE IS NOT AS HIGH BUT THE PROCESS SHOULD BE CONSIDERED COMPLEMENTARY TO NINHYDRIN EXAMINATION. THIS PROCESS DETECTS THE GREASY MATERIAL IN FINGERPRINTS WHEREAS THE NINHYDRIN DETECTS THE PRESENCE OF AMINO ACIDS, SO MARKS NOT DETECTED BY ONE COULD WELL BE DETECTED BY THE OTHER. FOR DEVELOPMENT OF FINGERPRINTS ON FABRIC, METAL DEPOSITION IS COMBINED WITH ULTRAVIOLET ILLUMINATION. THE DEVELOPED FINGERPRINTS ARE RECORDED ON HIGH-CONTRAST FILM PROTECTED FROM THE ULTRAVIOLET LIGHT WITH A YELLOW FILTER. TO DATE THE LABORATORY TESTS HAVE BEEN MORE PROMISING THAN THE OPERATIONAL TESTS. FURTHER TESTS ARE ISOLATING THE REASONS FOR THIS. DEVELOPMENT OF SIMPLIFIED EQUIPMENT AND ALTERNATIVE METALS IS ALSO UNDERWAY. A LIST OF FIRMS SUPPLYING THE EQUIPMENT IS GIVEN. CAUTIONS ARE GIVEN FOR WORKING WITH CADMIUM, WHICH IS A POISONOUS METAL. (GLR)