Krull,
A tip for bringing out hard to read engravings is to have the light source skim across the surface. This will cause hard shadows and they will bring out the detail for you. You will have to play with the exact angle, but somewhere around 80* to the surface would be a good start.
This technique works really well for petroglyphs also. I discovered the technique while visiting Indian Grinding Rock in Volcano, CA with my girlfriend at the time, who was Miwok indian. There is a large rock outcropping that has lots of petroglyphs, but you can only see them at sunset and sunrise when the sun is low in the horizon and the light skims across the surface of the rock.