Arai, Shigeo

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Northwestern University Illinois, School of Law: Scholarly Commons

Journal of Criminal Law and CriminologyVolume 43 | Issue 6 Article 121953Application of Electrolytic-Polishing to RestoreObliterated Letters on MetalShigeo AraiFollow 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 CitationShigeo Arai, Application of Electrolytic-Polishing to Restore Obliterated Letters on Metal, 43 J. Crim. L. Criminology & Police Sci.809 (1952-1953)THE APPLICATION OF ELECTROLYTIC-POLISHING TORESTORE OBLITERATED LETTERS ON METALShigeo AraiShigeo Arai has since 1949 been a police technician on the staff of the ScientificCrime Detection Laboratory, National Rural Police Headquarters, Tokyo, Japan,where he is particularly interested in the application of electrical engineering toidentification problems. In 1944 he completed a course in physics at Tohoku Univer-sity and has devoted time to research problems related to vacuum tubes. Mr. Arai isa member of the Japanese Physical Society.-EnrroR.The restoration of obliterated letters stamped on metal surfaces isgenerally accomplished by treating the area with a solution of cupricammonium chloride and other reagents. The restored letters may notbe so distinct, and the operations are troublesome. This author hastherefore experimented with the application of an electrolytic-polishingmethod and has obtained successful restorations.The method is applicable to various metals, and the operation can becompleted in a short time (about five minutes).METHODThe electric circuit diagram and the apparatus for the operation areshown in Figure 1. First the obliterated area is polished with sandaoeolterated aeACAz--cathode (absorbent cottondipped in electrolyte)Figure 1The Electric Circuit Diagram and the Apparatuspaper and then cleaned up with acetone. Next the area (anode) isrubbed with absorbent cotton (cathode) dipped in the electrolyte. Thecomposition of the electrolyte is described in the following paragraph.The voltage needs to be slightly higher than a critical voltage whichdepends upon the property of the particular metal, for otherwise thecurrent does not flow. If the voltage is gradually increased while rub-bing the area with the cathode, the current begins to flow when thecritical voltage is reached. Increasing the voltage about 0.5 volts more,SHIGEO JRI[3Figure 2Letters Restored in Brassthe rubbing is continued. Generally after three minutes of treatment,the letters appear on the surface. At this point the electrolytic-polish-ing is stopped, and the surface is immediately cleaned by washing withwater for a minute, followed by a neutralizing solution. The surface islightly covered with machine oil and photographed. In washing andneutralizing one must be careful not to rub the area too much, lest therestored letters should be erased.Table I shows the composition of the electrolyte, and Table II, thecondition of electrolytic-polishing. It is not necessary to follow theseexactly.Table ITHE COMPOSITION OF THE ELECTROLYTEDistilled water 500 ccSulphuric acid (conc.) 15 ccGelatine 1 gramCupric sulfate 1 gramCupric sulfate is used when the metal is a ferro-alloy and also when the letters arerestored with difficulty.Table IITHE CONDITION OF ELECTROLYTIC-POLISHINGApproximate current densityMetal Voltage (ampere/cm 2 )Carbon steel 6.0 0.19Brass 7.0 0.70Copper 6.5 1.9CONCLUSIONSThe reason why the letters are restored by this method is not exactlyunderstood. The author believes that the following theory may be theexplanation. The anode (obliterated area) is oxidized and dissolvedby the electrolytic-polishing. So the growth of rust and its dissolutionoccur on the anode surface. The stamped parts of the metal have apermanent set. Therefore, the energy required to take one atom ofmetal from the surface and to oxidize it (rust it) differs at those partswhere a letter has been stamped than where there was none. In thisway the letters are restored.[Vol. 43ELECTROLYTIC RESTORATION OF LETTERSFigure 3Numerals Restored on the Back-Sight of a Mauser PistolFigures 2 and 3 show examples of restored letters in experimentalcases. The author had erased the letters by filing with a rasp. Thephotographs were made after restoration.1953]

Application of Electrolytic-Polishing to Restore Obliterated Letters on Metal

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Application of Electrolytic-Polishing to Restore Obliterated Letters on Metal

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