| Summary: | Restoration of erased engraved marks is considered difficult compared to the
restoration of stamped marks, as the defonnation occurring to the metal due to the
engraving is minimal. Hence, a series of experiment were conducted to determine the
sensitivity and efficacy of various selected reagents to restore erased engraved marks on
aluminium surfaces, as this metal has been widely use in motorcycle engines and
firearms.
The experiments consisted of preparing several aluminium plates and engraving
them using a computer controlled engraving machine, Gravograph. The marks were
erased to different levels down to the depth of the engraving. Some selected reagents
were applied on the erased plates by swabbing etching technique to restore the erased
engraved marks. Two metallographic reagents: (1) 60% hydrochloric acid (HCl) and 40%
sodium hydroxide (NaOH) and (2) acidified ferric chloride solution consisting of 25 g
ferric chloride, 25 ml hydrochloric acid and l 000 ml of water were determined to be
sensitive, as both restored marks up to a level of 0.04 mm below the depth of engraving.
However, the above reagent (1) was considered to be the most sensitive one, as the marks
recovered by it were more distinct with no difficulty to viewing.
Experiments were also performed by erasing the engraved aluminium plates to
different levels below the depth of engraving and over-engraved with different marks. The original marks that had been erased were restored using 60% hydrochloric acid
(HCI) and 40% sodium hydroxide (NaOH). However, the depth of restoration decreased
from the original 0.04 mm (without over-engraving) to 0.03 mm.
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