Surface Damage on a $5 Cook Islands coin - what could have caused this?

 Hello All! I wonder if anybody can help me figure out what has caused this unsightly surface wear on this otherwise beautiful coin. If not for this, the coin would easily fall into the Uncirculated category as there is no other wear. The lustre is also excellent, but may not show in the photos, as it is a dull day here. My first thought was cleaning, but it doesn't appear to have ever required it. Any thoughts would be gratefully received. Cheers, AY

 The coin is made of Aluminium bronze, weighs 14.3g, and is 31.51 mm across. It was minted at the Royal Australian Mint, Canberra.

How was this holdered?  I wonder if there was a chemical in the holder…

Oklahoman

How was this holdered?  I wonder if there was a chemical in the holder…

Hi! It was in an ordinary, modern coin flip with inert materials. It doesn't appear to have had the green gunge on it that is often associated with old-school display/storage methods. Cheers, AY

I know it is not a bullion coin, could it possibly have been on the planchet prior to striking?  If not, it could be a spot that appeared after a planchet washing.

I have seen so many coins with milk spots that appeared.  They were related to the preperation of the planchet.

I will follow this thread.  It is an interesting question.

Oklahoman

I know it is not a bullion coin, could it possibly have been on the planchet prior to striking?  If not, it could be a spot that appeared after a planchet washing.

 

I have seen so many coins with milk spots that appeared.  They were related to the preperation of the planchet.

 

I will follow this thread.  It is an interesting question.

 

An interesting question, and not one that I am qualified to answer. I thought there may have been a coating or cladding on the planchet, which has deteriorated, but I'm unsure. There are no milk spots, as I understand them to be. Thanks for your interest. Perhaps someone will know more about it. Cheers, AY

Another thing I have wondered about is how to grade a coin such as this, where the detail is sharp, the coin unworn, and the lustre excellent but possessing a major flaw. Cheers, AY

Arthur Yapp

Another thing I have wondered about is how to grade a coin such as this, where the detail is sharp, the coin unworn, and the lustre excellent but possessing a major flaw. Cheers, AY

  For your information, I have a friend who is also interested in the answer to this question. So now you have two backward New Zealanders interested in the answer to the same thing.

Seventy views. And only one member knows enough to be interested. I do not refer to myself because I don't know the answer. That's why I'm here, soliciting experts and more experienced folks. Thanks, and with respect, AY

Arthur Yapp

Seventy views. And only one member knows enough to be interested.

I am one of the 70. I am interested. I do not know the answer to either question. I look forward to learning.

rsirian1

Arthur Yapp

Seventy views. And only one member knows enough to be interested.

I am one of the 70. I am interested. I do not know the answer to either question. I look forward to learning.

That is most encouraging. Thank you. AY

I know that this is a bit far off as a suggestion goes but - Maybe the alloy was not properly mixed /had impurities that over time reacted and caused this . 

As for grading - It would probably grade just like any other coin , just with a  side note for the toning /patina .

But that is just a guess , as I am no grading expert .

Alrumon

I know that this is a bit far off as a suggestion goes but - Maybe the alloy was not properly mixed /had impurities that over time reacted and caused this . 

 

As for grading - It would probably grade just like any other coin , just with a  side note for the toning /patina .

But that is just a guess , as I am no grading expert .

Hi Alrumon! Thanks for your post. It is as good as any other suggestion that has been made here. Oklahoman thought it could be something similar to what you are suggesting, and I don't believe it's an impossible scenario. I'm having the devil of a time with some 2016 Canadian Maples (bullion) where milkspots were caused by borax in the mix. The only thing I can think of against your suggestion is the reputation of the Royal Australian Mint, Canberra, where they were struck. But… mistakes get made by even the best of us. And experiments are carried out all the time. After cleaning, which I don't believe has ever happened, I would say this is the most likely possibility, now suggested in one form or another by the three of us.

 Thanks for your valuable input. Cheers, AY

I'm by no means an expert, but it looks chemical to me. I can't imagine how else you could damage it without causing any other type of issue. (E.g. extreme heat would probably cause blistering, cold would crack & probably wouldn't cause a colour change anyway).

Could it be someone acquired the coin, put it in a chemical solution for some reason (let's say to make it extra shiny), and then placed it in the holder without drying it off properly?

If the chemical solution has simply reacted to cause a colour change, that would explain why the detail is still there. Plus some of the “damage” appears uneven like it would after being in a liquid.

A friend of mine managed to turn a bunch of his copper-nickel 50p coins (which are normally silver in colour) into pale pink after leaving them in a chemical solution too long. Sadly I never saw them (otherwise I'd have taken them for the novelty value!), but apparently they were “perfect except for colour”. So no additional loss of detail but a considerable change in colour.

No idea what chemicals would do this, but it's the best answer I can think of.

 Hi, A Collector! I think it is starting to look this way, i.e. chemical. It could be as you suggest, but I have no way of knowing. I know for sure that the dealer who sold it to me would not have fussed with it in any way. He is a dealer, pure and simple, and does not even collect coins himself, so the culprit would have to have been someone coming before him. I have not attempted to remove these marks in any way. “This coin, if not unique, is certainly one of the few circulating $5 coins in the world (demonetised in 2016)” - I quote from the Numista comments. He saw it had an interest value and put it up for sale regardless of condition, and I was happy to buy it for 5NZD. The surface of the coin appears to be flaking off, but I am sure no colour change has been effected, apart from it now looks untidy and uneven, as you say, like it would after being in a liquid.

 The only chemical I can think of that may cause this sort of damage is isopropyl alcohol, though I have not experimented with it myself. Acetone, in my experience, is not worth wasting time with, and any others I cannot think of. I tend to leave coins alone, although I believe cleaning has a time and place. Perhaps the damage occurred by accident?

 Thanks very much for your input. Maybe your thoughts will ring a bell with someone else, and we will be able to solve this mystery together.

 Cheers, AY