I am just wondering how frosting was applied to proof dies prior to the current laser application process. I learned about the pickling (acid) method, that's the "wet etching" method. That's not what I'm wondering about. I'm wondering about the "dry etching" method. Was this a process of applying frosting to proof dies at the U.S. or other nations Mints? How was that handled? Also, what about the fields of the die? How did the fields not receive the etching from frosting? Did they cover the areas they didn't want frosted with something (taping?) Below: Coins (not dies) made with proof dies.
If the fields were covered with wax paint, etc. and then the die sandblasted the devices would receive the frosting rather than the fields.
sandblast the entire die (both the high and low points), then polish just the fields (high points of the die)?
@mlov43 http://www.coinnews.net/2013/10/04/how-the-philadelphia-mint-polishes-dies-to-make-proof-coins/
So, sandblasting was the "dry etching" method before the laser? Okay then! Thanks! BTW, I'm surprised the tape stays put on the surface of the devices with that power tool rubbing up on it. That's gotta be somma dat Gorilla-Glue Flex Tape stuff.
Thanks! That was the "wet" method? And I'm guessing that they used taping and diamond paste grinding as a standard procedure with acid etching?
"Sand" might not have only been silica. I've seen it done in a craft environment with crushed walnut shells.
The wet method involved soaking the business end of the die in acid. It frosted the entire surface. Then they would take a mandrill and polish the fields which are the high points on the die. Voila! Cameo!
Diamond paste yes but no taping as there is no need for it. When dies are polished it is/was done in a machine - not by human hands. The reason taping is not necessary is because the polishing wheel cannot touch and never touches any of the devices. The only part of the die that it can touch is the fields.
Well, I think we'd better these guys to knock it off: http://www.coinnews.net/2013/10/04/how-the-philadelphia-mint-polishes-dies-to-make-proof-coins/
Yeah I know. And if you keep looking you'll eventually find the article where they show the actual machine that polishes the dies and does the vast majority of the work. What the article you linked to is showing is what happens after polished dies have been inspected and found to need retouching. Think for a minute about how many man hours and how many employees would be needed to polish every die completely by hand. There wouldn't be one guy sitting at a desk doing it - there'd be an assembly line of them doing it ! The article itself states it takes "that guy" 1 to 3 hours per die. Split the difference and say it takes 2 hrs per die - that 4 dies per day. Think 1 guy could keep up with a modern mint ?
I'm not sure how the Korean mint does/did things (I know that's your focus). The US mint used the nitric acid pickling method up until 1970. After that, they transitioned to the sandblasting method mentioned above. Today, all proof cameos are created by laser. They gradually transitioned series through the early 2010's. This is an image that brg5658 created to show the different textures produced by the various methods:
