Ladysmith's thread about inlaying reminded me of something. I didn't want to hijack her thread with it, as it's not really relevant to what she was asking, but I wondered if it might be of interest to someone anyway.
As part of my job I have to make fairly large copper forgings, typically from 4" x 1/2" bar. Not very pretty things, but designed to carry thousands of amps of DC current into massive steel components for electro-plating.
These forgings have to marked, for the particular component they should be used for. The corrosive chemicals would strip off any kind of paint or ink marking, and the mechanical handling equipment soon rubs off etched or engraved markings.
However, because copper is so soft standard engineers letter punches will make a deep impression. Filled with silver-solder, and the surplus metal linished off flat it leaves an indelible, and and very resilient, mark in the copper.
No photos of the work stuff. But I do have this, very bad, pic of a copper bracelet that I marked using the same process. I will get to explore the decorative possibilities one day, when I get the time....
one_rod.