Gold, Platinum, Brass and Aluminium are the easiest metals to work on. I'm currently trying to engrave into some tablets for the Institute of Cancer Research www.icr.ac.uk. They are too soft and flake easily, preventing a clean cut. I've sprayed the tablets with lacquer, without luck. I've tried painting them with super glue, again without any success. Now I'm using a car paint spray on them.
This is a a joint project with Simon Armitage, the Poet Laureate. Simon_Armitage