Discussion
A solution of glacial acetic acid and hydrogen peroxide is useful for restoration of erased number from which of the following surfaces ?
Answer: C
The solution is useful for restoring erased numbers on lead.
Restoration works by etching the metal: the stamping left a zone of deformed, strained metal below the surface, and an etchant attacks that zone faster than the undisturbed metal around it, so the number reappears. Each metal needs its own etchant. For lead, such as a battery casing, the reagent given in forensic practice guides is glacial acetic acid with hydrogen peroxide.
The other surfaces use other reagents. Steel and cast iron are etched with acid mixtures such as Fry's reagent (cupric chloride in hydrochloric acid) or acidified dichromate, and zinc alloys with an alkaline or chromic acid solution. Stainless steel needs its own acid etchant.
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