How do the devices get their frosty appearance? Are the die's device areas treated with some sort of substance? I can't imagine it being any sort of bead blasting, burnishing, etc. done selectively to the devices with a solid die... And, what about the fields, are they simply rouged with heavy polish? And if the device areas of the die are given an additive, what sort of substance causes that frosty finish on these cameo and deep cameo coins?
A completed die has that finish all over. They're more matte than polished, and for the first certain number of strikes are capable of transferring that frost to the coin until the surface irregularities smooth out from wear. Look at some mid-1880's Carson City Morgans for that in action. Every die has the fields polished before being put into production. This turns them into reflective surfaces rather than matte.
So it's simply the inherent quality of the newly finished die, without any treatment to the die's device areas? And, subsequent strikes will cause the surface of the die's devices to "wear" and consequently cause less and less frostiness to transfer onto the coin? If that's the case, it seems incredible that such frostiness can come about, from raw metal die to raw metal planchet. Unless you mean that's how the finished dies come out - with whatever finishing treatment they're given that causes that frostiness, prior to polishing the die's fields.
These days, the Mint employs lasers to actually etch the devices of dies to achieve that frost. Back in the Classic days, it could have been done with acid etching.
That makes sense. Metal does seem to naturally exhibit that frosty appearance when getting pressed, beyond mere light reflections, such as on this elongated coin below (pic from 'net). The new surface of the devices on the die must be rough.
Early devices were acid etched. Then sandblasting was used. Now, laser etching is the norm. The fields on the die are then polished and planchets pf the highest quality are struck. Often twice. At slower speeds, and higher pressures. More attention is paid to strike and die setup. So begins the life of a cameo proof.
You may find this thread I wrote interesting (it's almost 4 years old, but still relevant). In brief, from 2006-2011 the US Mint in particular started employing laser etching of dies to get the "frosty" look. IMO, they ruined USA proof coinage. See the picture compilations I show below...judge for yourself. And, here is what the "20" of the "2011" Proof Lincoln Cent looks like up close. Those little "bubbles" are the way that laser engraving achieves the frost look.
I agree that the new "Laser Engraving" has completely ruined the current generation of Proofs. It looks absolutely atrocious. Just one more way the US Mint has "improved" coinage.
Nice write-up. Thanks for that link. I agree - I much prefer the older type. A lot of the details are lost with the heavier and darker "frosty" finish. But, it also appears as if the relief became flatter, in a span of just a few years (even over one year from 2009-2010 the details look flatter); the 3D effect consequently looks diminished, and the more intricate details along with it.
For which era are you referencing? There are a number of variations in production techniques, especially after 1950, that make these cameo coins more plentiful.
Working dies were treated with an acid solution, then the flat surfaces were buffed with an emery wheel and fine "flour" emery, yielding frosty devices and mirror like fields until flow lines developed as the dies were used. Planchets were also treated with an acid solution that made them a bit frosty as well. see Burdette, "From Mine to Mint," p.399
