I was just wondering about PAST practices at the U.S. Mint, since I am writing about developments at the Korean Mint in the 1970s to 1980s. They also transitioned around this time from pickleing to sandblasting (circa 1983~1985). The Koreans only started making frosted proofs in 1975. Also, the U.S. Mint, as well as other major mints around the world (Osaka, Britain, Austria, La Zecca in Italy, etc) were big influences on the Korean's mint operations. Which makes sense, since the Koreans were trying to learn from, and then compete with (and later take over!) the best of the best in the world. Nowadays, I'm sure that lasers are also used to apply frosting, but their frosting looks different from that "gritty" looking laser treatment on that dime on the far right in your composite photo you uploaded.
Ah, this is re-touching! Yeah... I kinda thought that this would be insanely labor-intensive. How easily I suspend disbelief... Good to know. Thanks, Doug! Oh, and uh...
A mandrill?? Whoa. Try pickin' this fella up and using him to polish the fields. Good luck to you, sir.
Merely for the purpose of clarification and understanding, the mint switched back and forth between sand blasting and acid etching many times. Usage of both methods dates back to various times in the 1800's. And with any luck, at some point in the future, they'll switch back to it again because what they are doing now is atrocious !
edit - Just as a note of interest, all business strike dies are polished in the same kind of machine. And while the machine in the video is the modern version, a machine of that same basic design has been in use for well over 100 years, that much is documented. And probably 200 years, though I have never been able to pin down the exact date as to when they first started using polishing machines on dies of Proof and/or business strikes.
