What Causes This?

I've had my "eyes on" S. Korean 10 Won coins now for about ten years. I've seen hundreds of coins in-hand, and hundreds more via macro-photography on auction/retail sites.

A little background: 10 Won coins were some of the first coins struck by the Korean Mint, starting in 1966. I came to learn that these coins were struck with dies manufactured by John Pinches of London (at least the first few years were), a private mint operating in Britain at the time. They also made the master dies.

There are certain strike characteristics concerning South Korean 10 Won coins minted in 1966 that I have seen again and again.

1) An overall "roughness" of the denomination numeral at its center: The middle stem of the "1" and the left side of the "0". This looks almost to be "bag marks" on these coins, as it looks like wear, or even scratches. Could this roughness come from the dies themselves?



2) A "mushiness" or "blobiness" on the eaves of the Pagoda on the other side: Some of these coins have "full eaves" with less mushiness, and some much more, like the image at the top that you see below. What causes this?



Some more examples:


Again, it seems that these are characteristics of the 1966 strikes only. I don't think that I've ever seen these same things on later strikes of the 10 Won coin. Here's a very typical example of a 1967 strike in UNC.

Full Pagoda eaves

No scratches on the denomination numeral.


Any of your knowledgable insights would be helpful...

 

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Are the planchets the same metal compositon?
Was there a change after 1966?
Have you seen any 1966 without the marks in question?

 

Interesting that there is one 1966 10 WON on Ebay with the same characteristics!
(These images I want to share with you are from Ebay.. not my coin)


Wait are you the person selling this coin?

 

Yes, planchets are all 88% copper, 12% zinc for these coins, from 1966 to mid-1970.

I really haven't noticed the scratches/roughness ever being absent on 1966 strikes, but the blobbiness of the eaves is on a continuum from very blobby to almost full eaves.

 

No.

 

But it's the exact same coin with the exact same background..

I can't think of anything besides this.. since 1966 had the lowest mintage maybe the Die or Dies that were produced had some kind of issue in that area.

 

Maybe it's localized die wear, like the start of the die wearing out.

I've seen similar melting burst patterns on worn die examples of US coins.

There's also some die deterioration doubling going on near the upper right edge.

 

@mlov43

It could be from grease and debris accumulating on the die in a thin layer. Take a look at the obverse of this 2001D Kennedy. You can see a similar roughness in its surface along the outer edge.

Chris

 

Did NGC designate this Kennedy Half as a Mint Error, or some such designation?

 

All later coins seem to be good, full strikes with the same exact design, "real estate"-wise.
So the coining presses were set with higher striking pressures in subsequent years?

 

Yes, but not for this.


Actually, I was a little surprised that it was graded MS64 because of the obverse. I concluded that the graders considered this grease & debris on the die.

Chris

 

Thanks for your insights. This is helpful.

Another noticing of mine: I also seem to detect a higher relief of the devices on these early 1966 strikes, too. They seem slightly more raised. Perhaps the dies in later years had "shallower" engraving, resulting in sharper strikes? Hmm.

 

I think this is the first time I've ever seen this kind of error.

Way cool, dude.

 

Thanks! One of only two known for this denomination/date/mintmark.

Chris

 

There are plenty of coins missing a clad layer. It's just not that common to find many of any one date/mintmark. The clad layer usually separates at the end of a roll of planchet metal, and it falls away when the planchets are cut. Half dollars would be the easiest for a Mint employee to spot after striking because of their size. It's usually when the side missing the clad layer is facing down that it is missed. I found mine in a Mint bag, and it stood out like a sore thumb.

Note: One of our members collects MINT Errors of coins missing the clad layer. He has amassed quite a collection.

Chris

 

What Causes This?




uh, freezer burn?

 

Definitely from the die not fully filling the areas where the most metal is required.