Restoration of obliterated hallmarks

I am a librarian for a science institute that handles much of the
forensic science for the New Zealand Police.
One of our forensic scientists has requested that I find out details on
the recovery of hallmarks (or similar engraved marks) that have been
obliterated from jewellery, in particular gold rings.
There has been little done on this subject, one or two reports about
using Aqua Regia, but details are sparse.
If anyone can help me please email me at: snipped-for-privacy@esr.cri.nz
Thank you