Disregard that last bit about crayons and paper. I have been informed that it's a practice that is now frowned upon beause it can cause damage to the microstructure.
Good digital photography is the solution.
I remember 4W's useful hint of rubbing with grass. I suppose this would now be a no no because it involves rubbing the carvings.
Is this a plot by the manufacturers of digital cameras?
Wanna buy some crayons?