It is known that restoration of erased engraved identification marks on the engine and the chassis of a car or on a firearm has low success rate.
Unlike stamping, engraving on a metal surface leaves no pronounced, permanent subsurface deformation in the crystalline structure, also called
dislocation that can be revealed by suitable methods. Hence, the current research work investigated whether metallographic reagents used in the
restoration of stamp (compression) marks could be applied to recover engraved marks on steel surfaces and also to establish the sensitivity and
effectiveness of some of these reagents for the restoration of the marks.
Experiments were conducted by mechanically engraving alphanumeric characters on several steel plates using a computer controlled engraving
machine called Gravograph. The markings were later erased from the above steel plates by removing the metal in stages of 0.01 mm through
0.04 mm below the bottom of the engraving. Several plates were thus prepared wherein each one had been abraded to a specific depth. Then eight
metallographic reagents were tested on each one of the above erased plates using a swabbing technique. The results had shown that while most of
the reagents were able to restore marks up to certain levels of erasure, the reagent 5 g copper sulphate, 60 ml water, 30 ml concentrated ammonium
hydroxide and 60 ml concentrated hydrochloric acid restored marks erased to a depth of 0.04 mm below the engraving depth, thus presenting itself
the most sensitive reagent. Quite significantly, the above reagent was also able to decipher successfully the original engraved marks that had been
erased and engraved with a new number, or obliterated by centre punching.
The results of this research work should benefit the forensic practitioners engaged in the serial number recovery on vehicles, firearms and other
objects.