Engraving, I didn't actually mean etching in the acid etch sense but, moreover, engraving is the right word. And it's copper, not gold nor silver. . Raw copper will keep its brilliance as long as it's not touched with body oils from handling, and stored in a dry place. The toning on the uncarved surfaces is probably from the owner rubbing it with a cloth 100 years ago. Or just toned naturally when it was formed into a sheet before being cut into the award, perhaps some oil was applied then and it took some year to tone it. . . In further review of you photos; Pink, that's the tone you get once somebody cleaned it with a light chemical. I suspect it had gotten some toning but tooth brush and light cleaner was used on it. It wouldn't have cleaned the darker toned areas B/C they prob got a bit of oil on them, but brought back luster in areas that were never touched. Otherwise the tone should be brilliant red. the chain's color ought to be red toned verses pink too.
I too, had jewelry class in collage, and collected pennies as a kid, still have most too. You might discuss preservation with a coin collector 'penny' expert as, if this has been cleaned, for the pink tone, "If" then, you'd want to be doing something to stop it from tarnishing again. I lightly cleaned otherwise 1960's mint pennies that I'd improperly stored back in late 70's, big mistake. Not too big because 1960's pennies are still just crap, but, after a few years, the toning continued to go darker, and it sucked. Once cleaned, the microscopic surface of copper is etched, it'll cause it to tarnish more rapidly, er somtin like that.