Restoration of Obliterated Stamped Marks on Aluminium Surfaces by Metallographic Etching Technique

Serial number restoration is a frequently encountered problem in forensic science laboratories for the investigation of theft and burglary cases. These identification marks are generally introduced over metallic surfaces of different vehicle parts and firearms by various means. Chemical etching is one of the most effective and simple technique to restore obliterated, erased, over-stamped and over-engraved marks on metallic surfaces. Several significant studies on restoration of engraved markings on aluminium surfaces were previously reported. The present study attempts to find out an efficient and fast etching reagent to restore obliterated stamped marks on aluminium surfaces. Ten effective etching reagents previously reported by various researchers in their restoration studies were assessed in the present experiment. Etching reagents were individually applied on obliterated surfaces by the cotton swabbing method. The Reagent 3 (ferric chloride 25 g, conc. HCl 25 mL, distilled water 100 mL) was found out to be the most sensitive and rapid (4-6 min) for the restoration on aluminium surfaces. The study also revealed that the absence of an alkaline compound in etching reagent potentially accelerates the speed of the restoration process.