when we cave, we've noticed that brighter light washes out detail
on faint scribe marks on the rock.... (old signatures mostly)

so we use a low-power light source and side-light the area --
I've thought that the spectrum might be important also
because when I caved with a guy using a carbide lamp, that sort
of detail was clearer than with an electric lamp....
carbide is a softer, yellower light...

seems there might be some computer technology out there to
enhance an image?

Deb

PS  I've used rubbings on old gravestones around here, with some success,
but there was always at least some relief left -- that is the key