Forensic Ballistics: Restoration of Erased Markings on Metal Surfaces

UGC-NET Forensic Science Unit V advanced drill on the restoration of erased stampings on metal surfaces such as firearm serial numbers and vehicle chassis numbers. Hard-band coverage of the metallurgical basis for restoration (the cold-worked strained zone created by the original stamping tool, which extends below the visible face and survives surface obliteration by filing, grinding or peening), differential dissolution chemistry (strained grains dissolve faster in selected etchants than unstrained ones, exposing the latent pattern). Coverage of reagent systems for each substrate family: Fry's reagent (cupric chloride, hydrochloric acid, water), 5 percent nital and the photographic developer method for plain-carbon steel and iron; Davis reagent, Villela's reagent and glyceregia for stainless steel; sodium hydroxide with hydrofluoric or nitric activators and Tucker's reagent for aluminium and its alloys; cupric chloride in hydrochloric acid, ferric chloride and acetic acid systems for copper, brass and lead. Non-chemical methods are covered as well: magnetic particle inspection (restricted to ferromagnetic substrates), ultrasonic relaxation and heat-tinting with its oxide-colour scale. Indian casework coverage spans chassis-number cases under Section 192A of the Motor Vehicles Act 1988 and firearm serial-number restoration under the Arms Act 1959 Section 25 read with the Bharatiya Nyaya Sanhita 2023.

Calibrated for MSc Forensic Science and BSc Forensic Science finalists targeting top-decile Paper II scores in firearm-toolmark and questioned-document overlap topics, for NFSU MSc Ballistics entrance aspirants, and for FACT-track candidates working toward central forensic-science laboratory posts in ballistics and questioned-marks divisions.

Topics covered:

• Cold-worked strain zone theory and depth below the tool face
• Differential dissolution rate of strained versus unstrained grains
• Fry's reagent, nital and photographic developer methods for steel and iron
• Davis, Villela's and glyceregia reagents for stainless steel families
• Sodium hydroxide with activator and Tucker's reagent for aluminium alloys
• Cupric chloride, ferric chloride and acetic acid systems for copper, brass and lead
• Magnetic particle, ultrasonic and heat-tinting non-chemical methods
• Indian casework: chassis numbers under Motor Vehicles Act 1988 and firearm serials under the Arms Act 1959

Sit this paper after revising the restoration chapters in Sharma B.R. and Heard, and consult ASM Handbook Volume 9 for etchant chemistry.

Allow 30 minutes.