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Unfinished Proof Dies VS a MS Grading

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Proof is a striking process, and includes not only polishing the dies (the finishing process), but also higher striking pressure and multiple strikes.

 

Since the only coin that you are referring to is that bullion piece, the ONLY difference between the MS die and the "unfinished proof die" is that the mintmark had been added to the die.

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coolcoin,

 

There is no difference in proof dies and MS dies. They are the same, but before striking proof coins, the die will be polished. This contributes to the cameo effect that proof coins generally have.

 

For bullion pieces, MS pieces do not have mintmarks, but the proofs do. So to create a proof coin, you have to add the mintmark, then polish the die. In this case, someone picked up a die that had a mintmark added, but had not been polished.

 

This is actually pretty common in Mint history, except that normally, a die has a mintmark stamped on, say a D, and then instead of polishing off the D and adding a different mintmark, a S is added over the D, creating a S/D variety.

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Modern proof coins are minted from highly polished dies using specially prepared blanks with a bright surface. Extra pressure is used to strike the coin and often the blank is struck more than once. They are the result of a number of labourous processes. Firstly, the die surface is sand blasted and hand polished using diamond lapping paste applied with soft wooden sticks. A final polish to produce a brilliant mirror finish is achieved with a dental drill covered with a soft pad. Next, the surface of the die is covered with clear tape and a scalpel is used to expose the design areas. Again the die is sand blasted resulting in a frosted finish on exposed design areas. The final process is for the die to be crome plated before being used to strike coins.

 

The blanks intended to become proof coins are also given special treatment. Prior to striking, they are immersed in a weak acid bath to remove any surface impurities. From that point on, they are only ever handled with gloved hands or special tongs to ensure that the surfaces remain pristine.

 

Coolcoin

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I believe that proof dies are also basined and that this involves grinding the surfaces flat. MS coins do not have the flat surfaces like a proof. Perhaps someone can help us on this.

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I think over the long years, the Mint has used several different methods of producing specimen-grade coins. It could very well be that you're all correct, depending on which coin you're talking about!

 

EVP

 

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For many years the proof dies were basined to further enhance the coin's appearance raising the devices on the coin's surface. I am not sure that they still do this operation

 

One other point: it does not make sense to me to plate dies (except for maybe a flash of electroless-nickel) because they are going to turn around and have to remove (grind off) this material every time they resurface the dies? tongue.gif

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I am sure the crome plating brings out the mirror like surface of the coins once they have been struck. Look at a cromed piece of metal. It too looks like a mirror.

 

Coolcoin

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I believe all dies are now basined. This gives the center of the coin a higher relief than the edge and allows the metal to flow outward from the center at the moment of impact, when the die pressure causes the surface of the planchet to heat and liquify.

I've never read or heard of a die being plated. A car bumper is shiny from plating but won't have flow lines.

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  • Member: Seasoned Veteran

Basining of the dies is not something unique to proofs. It's been done routinely at the U. S. Mint going back to the 19th Century. This is performed to give the dies the desired curvature to their fields, known to coiners as the radius. As noted above, this is done to facilitate metal displacement, thus sharpening the strike and increasing the lifespan of the dies.

 

As for chromium plating, the U. S. experimented with this in 1928 but didn't adopt the practice at that time. It has been done routinely with proof dies since the early 1970s to improve their lifespan. The brilliance of proof coins is the result of die polishing and has nothing to do with chromium plating, though the plating permits the cameo finish to last beyond the first few hundred strikes. This is why cameo proofs became much more common after 1970. I believe the currency coin dies are also chromium plated in recent years, again for durability.

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The atomic pore structure of crome is smaller than the atomic pore structure of the material to which it is attached to. Its ability to accept a mirror finish is greater than the ability of the material to which it is attached to even if it has been polished.

 

Coolcoin

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