What causes silver toning on Lincoln proofs?

[Bugmann1974]

I picked this up yesterday and it got me wondering how this happens. How does copper turn silver? I have another one similar to this in an intact proof set but with much less silver and I know I have seen others.

 

[Bugmann1974]

Here is a better picture of the obverse.

 

[TJ'S Coins]

This looks to me like something unnatural has been done to the coin.

[robec1347]

I've got one of those also. I don't know what causes it, but I like it.

 

[MarkFeld]

This looks to me like something unnatural has been done to the coin.

I'm not convinced of that. I think it is due to the the alloy and have seen that look on many bronze cents.

[RareSov]

I'd bet the alloy. Could be a mixing problem ?

 

A year or more ago, an aussie 20c (cupro nickel) was auctioned. The silver looking surface had spots of unmixed metal (copper) that had risen to the surface and set in dots. It fetched a huge price, and is believed to be unique. I'll see if I can find a pic

 

 

Bronze is a metal alloy consisting primarily of copper, usually with tin as an additive, but sometimes with other elements such as phosphorus, manganese, aluminium, or silicon.

 

Didn't know that..

[BillJones]

For some years, the mint holders had something in them that caused the coins to turn. You see a lot of this on 1970 Proof sets, and one of the years in the mid 1990s (I don't follow this stuff well any more.) was bad too. It also might have something to do with the chemicals that the mint used to clean the planchets before striking. If the material was not neutralized properly, the coins could very well turn. You see this on 1912-D and S Liberty nickels.

 

Finally improper storage can tone the coin too. If you store your Proof sets in places where the temperatures go up and down, you can expect the coins to go bad.

 

[WoodenJefferson]

Do not place proof Lincoln cents next to the defroster vent on the dash board of your VW Bug. The hamster in the blower fan cage emits uric acid fumes and this could be misconstrued as AT.

[Coindude]

I can't see your pictures at work... but I'll tell you from my experience. I had a box of unopened SMS's.... 1966 to be exact. Turns out two of the cents had a very silvery tone to them. To me, they looked like they came one right after the other, which wouldn't shock me but would be rare. But what it really looked like to me was that possibly a dime might have been struck and then one cent and then the next. Because the amount of silver tone lessened from one coin to the next. Just one possibility of many, but I think it is at least plausible... and if the Mythbusters were here... I think they'd have to agree!

[RareSov]

Hmmm packaging.. looks more like packaging toning, more even

[kryptonitecomics]

I have owned several....a modern Proof.....seen here:

 

The was graded NG PR69RD in an older NGC slab...

 

 

 

 

and this PR65RB IHC that when titled in either direction had a 50% silver and 50% hot pink yin and yang reverse. Quite bizzare but stunning to look at in hand ....this picture doesnt show off the mirrors

 

[RareSov]

Wow look at that one ! nice thanks for posting those

[James_OldeTowne]

In my experience, that kind of electric-blue tone is caused by the mint proof holder itself. Having had to catalog and look at dozens and occasionally hundreds at a time, you will find a surprising number of cents that tone in that manner.

[L1ncolnF4n]

Copper is rather reactive, and proofs demonstrate this even more. I've got a 2002-P Lincoln graded MS-68RD by PCGS that I just discovered has a lovely silver tone all over the obverse.

[Bugmann1974]

Thanks for the opinions guys! I wasn't sure if it was really toning or like some of you guys expressed here, an poorly mixed alloy. I was leaning towards an unmixed alloy.

My brain still wants to say that it is an unmixed alloy because it looks more like a patch of chrome than a tarnished area.

 

To you guys that say that it is the fault of the holder... Have you guys actually had some of these turn while in your possesion?