Davis, Charles A.

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Northwestern University Illinois, School of Law: Scholarly Commons

Journal of Criminal Law and CriminologyVolume 48 | Issue 4 Article 151958Restoration of Eradicated Serial Numbers by anInexpensive Electro-Acid-Etch MethodCharles A. DavisFollow this and additional works at: https://scholarlycommons.law.northwestern.edu/jclcPart of the Criminal Law Commons, Criminology Commons, and the Criminology and CriminalJustice CommonsThis Criminology is brought to you for free and open access by Northwestern University School of Law Scholarly Commons. It has been accepted forinclusion in Journal of Criminal Law and Criminology by an authorized editor of Northwestern University School of Law Scholarly Commons.Recommended CitationCharles A. Davis, Restoration of Eradicated Serial Numbers by an Inexpensive Electro-Acid-Etch Method, 48 J. Crim. L. Criminology& Police Sci. 459 (1957-1958)RESTORATION OF ERADICATED SERIAL NUMBERS BYAN INEXPENSIVE ELECTRO-ACID-ETCH METHODCHARLES A. DAVISThe author holds the position of Chief Technician in the laboratory of the Investi-gation Division, Indiana State Police. He has held this post for the last ten years andhas been a member of the State Police for fifteen years. His special fields of interest inthe laboratory include microscopic examinations, chemical analyses, and firearms in-vestigations and identifications.-EDrroRThe use of electricity in the restoration of eradicated serial numbers in metal hasbeen suggested as a means of speeding up the acid-etch method. Some of the equip-ment that has been suggested is rather expensive (1, 2, 3). A simple, inexpensivemethod is described in this article which is easily within the most limited budget, andit is just as efficient as more expensive equipment.The problems facing the police investigators where the method is used are varied.The usual problems are the identification of guns, typewriters, calculating machines,any kind of tool or instrument which is identified by a serial number in stampedmetal. Thieves who steal such equipment frequently eradicate the serial number bygrinding or filing away the part of the surrounding metal so the equipment cannot betraced through the number and identified.The act of stamping the numbers in the metal changes its structure beneath thesurface of the metal depressed by the die. Treatment of the metal so altered enablesthe investigator to reproduce the stamped number so that it becomes visible again.However, before such treatment is initiated, it is necessary to prepare the metalsurface.The scratches left by the eradication must be carefully removed by using abrasivematerials such as sandpaper and emery cloth. Remove only enough metal to eliminatethe scratches; start with the finest abrasive that is practical and as the depth of thescratches is reduced, use successively finer abrasives until the metal surface is actuallybeing polished. The more level, smooth, and highly polished and mirror-like thesurface, the more successful the restoration.After all scratches have been removed and the surface of the metal highly polished,the etching process is started. The best etching solution for steel is 50 % hydrochloricacid with 5 gins. of cupric ammonium chloride added for each 100 ml. of solution.This solution is stable and may be kept indefinitely in glass containers with glassstoppers. To prepare 50 % hydrochloric acid, add one volume of concentrated hydro-chloric acid to an equal volume of water. (Always add acid to water never add waterto acid.)The etching solution may be applied with a cotton swab attached to a glass rod ora wooden stick. The etching will be speeded up, and better definition will be obtained,if an electric current is permitted to flow through the etching fluid. An ordinaryflashlight battery may be used to supply the electrical current. Solder an alligator459CHARLES A. DAVISFigure 1clamp to a piece of wire about 12 inches long, this wire will ground the circuit to themetal to be etched. The ground wire goes to the positive pole of the battery. Anotherwire about 12 inches long is attached to the cotton swab by enmeshing it in the fibers;this wire completes the circuit by being connected to the negative pole of the battery,and the current will flow when the swab is touched to the metal (figure 1). The cottonswab is dipped in the etching solution and then gently rubbed over the polishedmetal. The speed of etching can be controlled by varying the position of the wire onthe cotton swab. Faster etching may be produced by placing the wire near the endof the swab close to the metal being etched, and slower etching is effected by placingthe wire on the end of the swab away from the metal being etched. Stopping themovement of the swab across the metal will cause pitting and is to be avoided. Slow,steady strokes across the metal as if one were painting with a light' brush will pro-duce the best results. If too much metal has not been removed, the numbers willbecome visible as the less dense parts of metal are etched, leaving the numbers moreshiny and slightly raised above the surface. Usually a few minutes is enough to restorethe numbers.If by chance the poles of the battery are reversed, and electroplating of copperoccurs on the metal being etched. The appearance of such a metal coating is a signalto reverse the poles of the battery.Tests on metals other than steel should be made before using the etching solutiondescribed. It might etch too rapidly. The solution may be diluted by adding waterslowly while stirring. Frequent tests will indicate the proper strength for the metalbeing etched. Make tests on portions of the same piece of metal bearing the serialnumber but not at the location of the serial number.[Vol. 4819571 RESTORATION OF ERADICATED SERIAL NUMBERS 461REFERENCES1. ARAI, SHIGEO: The Application of Electrolytic-Polishing to Restore Obliterated Letters onMetal. JouN.L oF CRmiILN. LAw, CR=TNOLrOy AND POLICE SCIENCE, Vol. 43, No. 6, 809-811. Mar.-Apr. 19532. WVEKnmD, RICHARD: N.A.T.B., Branch Office Detroit 2, Mich., 906 Fisher Bldg. Personalcommunication: (The N.A.T.B. agents routinely use an acid-etch method where the currentis supplied through a rectifier from 110 volts A.C.)3. ToRiER, RALPH F., Assoc. Prof. of Police Adm., Mich. State Upiversity, E. Lansing. Mich. Personalcommunication: (Mr. Turner stated that a method similar to that described in this article isunder study in his department.)

Restoration of Eradicated Serial Numbers by an Inexpensive Electro-Acid-Etch Method

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Restoration of Eradicated Serial Numbers by an Inexpensive Electro-Acid-Etch Method

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