Copper spots on gold

[RWB]

Is anyone aware of chemical tests being performed on the so-called "copper spots" that are common on gold coins? Are these really copper or copper oxide, or something else such as iron oxide?

[physics-fan3.14]

Is there enough (or any?) trace amounts of iron in the alloy to cause noticeable spots?

[coinman_23885]

Is anyone aware of chemical tests being performed on the so-called "copper spots" that are common on gold coins? Are these really copper or copper oxide, or something else such as iron oxide?

 

I don't know the answer to your question, but I do know that NCS (the conservation division of NGC) stated that they had developed a chemical formula to remove copper spots. It is my understanding that it isn't a standard dip. In order to create such a formula, NGC would presumably need to know the answer to your question. I would contact them.

[Afterword]

Gold coins contain silver and/or copper, both of which can tarnish. Are not the spots simple tarnish?

[RWB]

Late 19th and 20th century gold coins contain no silver and certainly no iron, which would make the alloy brittle. Electrolytic refining greatly improved the purity of refined gold, silver and copper used by the mint.

 

Copper and gold are in a well-mixed alloy. Copper oxide might be present also due to annealing. But it is difficult to understand how a few clumped atoms or molecules could create the extensive "copper spots" often seen.

 

I'll check with the NCS folks about their thoughts, and thanks for the suggestion.

[thebeav]

While on the subject, I'll be the first to say that these spots on gold don't bother me at all.

Whereas a black spot on a copper coin gives me the creeps.....

 

Paul

[RWB]

Sometimes the copper-colored spots are unobtrusive, but on other coins they are visually intrusive. I'm not searching for a way to remove them, but information on their chemical composition. Also, do they involve the alloy or are they superficial?

[Afterword]

"Copper and gold are in a well-mixed alloy."

 

This suggests to me that a localized concentration of accelerant might be required to create these copper spots. Not something in the air, but foreign matter that has somehow come in direct contact with the surface of the coin.

 

Something highly reactive with the impurities of the gold.

 

 

 

[RWB]

Copper is the only other metal above the ppm level.

[GoldFinger1969]

Roger, what do modern gold coins utilize to harden the coins ?

 

If the Liberty's/Saints had copper (and/or trace amounts of silver), when did other metals replace copper in gold coins ?

[BillJones]

Sometimes the copper-colored spots are unobtrusive, but on other coins they are visually intrusive. I'm not searching for a way to remove them, but information on their chemical composition. Also, do they involve the alloy or are they superficial?

 

In my opinion, and I'm no chemist, is that they are made of improperly mixed amounts of copper in the gold - copper alloy that are on the surface. In my view they are something that is akin to red copper coin that turns brown, except in this case it is brown spot in the middle of gold coin which makes it obvious. Sometimes the copper is generally mixed over the surface, and tones with the gold to produce a wonderful warm golden - coppery appearance. Such coins often bring premium prices.

 

As to fixing them, that is tricky and quite often counterproductive in my opinion. The accepted way is to dip the gold in a solution to lighten the copper spot. The trouble is most of these spots are more than skin deep, and after a year so they tend to return, often more unattractive than ever.

 

There are other kinds of spots. These are impurities that are something other than copper, like a cinder or something like that. Quite often these spots are black, ugly and into the surface of the coin. They might be a struck through or something that got into the bullion when it was in the refining or alloying process. Usually there is nothing you can do about these things, and attempts to lighten them usually make the rest of the coin look worse.

 

My philosophy is leave copper spots alone. Quite often the fix is only temporary, and the buyers of such coins are often quite unhappy when they crop up again after they have bought the coin.

 

One prime example of this problem I observed was on some of the coins that were recovered from the SS Central America and curated. I noted about 20 years ago that some of these coins were going to turn, and when they did the results were not pretty. The coins had big brown copper bloches, and ugly as sin.

[RWB]

The small black bits are copper oxide.

 

I'm skeptical of the "improper alloy mix" because of the care taken to have a homogeneous alloy, and the multilevel inspections, and annealing. If excess copper were on the surface, it would oxidize very quickly especially in the presence of light lubricating oils. (Mixing of gold and copper has to conform to fluid dynamics and heat transfer within liquid metals - these tend to support discrete boundaries between elements, especially when one is nearly inert and the other is moderately reactive.)

 

Any metallurgists running around the message boards these days?

[Nutmeg Coin]

As to the cause I don't know about that. On what the conservation/restoration service uses, I heard it was something like nitric acid, dissolves the copper but not the gold. Some people used to use strychnine. The problem with the critical analysis of gold coins with copper spots is that a lot of buyers don't want them and either return them or offer to buy them at a discount like Rarcoa. CAC doesn't have a problem with the spotted coins in many cases and I was surprised what stickered with them. The alternative for higher grade type gold coins was the copper spot removal option which is relatively cheap.

[coinman_23885]

The small black bits are copper oxide.

 

I'm skeptical of the "improper alloy mix" because of the care taken to have a homogeneous alloy, and the multilevel inspections, and annealing. If excess copper were on the surface, it would oxidize very quickly especially in the presence of light lubricating oils. (Mixing of gold and copper has to conform to fluid dynamics and heat transfer within liquid metals - these tend to support discrete boundaries between elements, especially when one is nearly inert and the other is moderately reactive.)

 

That's interesting. To broaden the discussion, toning is also directly related and very relevant. I think the improper alloy mix explanation is the only thing that could explain the natural toning (IMO) that I have observed on St. Gaudens Double Eagles. It is extraordinarily rare and I have only seen a handful or so, but the pieces exist and I believe the pieces are naturally toned. I cannot think of another mechanism, especially given the stability of gold alloys, that could produce the pattern (and it is common to most of those I can recall seeing). I am obviously very biased as I owned a toned Saint. The piece has a copper look in the toning, and it also interestingly has copper spots. I know it is speculative, but it is the best that I can do without sending my piece off to a lab (which I would never do).

 

 

 

[BillJones]

Here is an example of how extreme the anti-copper spot attitudes get. Years ago I had this 1907 High Relief $20 gold on consignment. When I offered it for sale, a number of dealers rejected instantly because of the minor copper spotting on the bottom of the reverse around the area of the sun. This is a really beautiful example with fully original surfaces, and yet some very minor spotting in a area that was out of the focal point of the design put the coin on the reject list.

 

 

This coin was graded MS-64, and yes I can see why CAC would give its approval to a gold coin with minor copper spots. There is nothing wrong with them if they are light and do not detract from the eye appeal of the piece.

[Afterword]

"...improper alloy mix..."

 

 

 

 

Considering the number and variety of error coins the mints have produced over the years, it is not a theory I would reject out of hand.

 

As for the toning on your St. Gaudens - it is decidedly NT or AT.

[MarkFeld]

"...improper alloy mix..."

 

 

 

 

Considering the number and variety of error coins the mints have produced over the years, it is not a theory I would reject out of hand.

 

As for the toning on your St. Gaudens - it is decidedly NT or AT.

 

There's nothing AT about it. And repeating "it is decidedly NT or AT" doesn't make a blatantly original looking coin questionable or a blatantly AT coin other than AT.

[Afterword]

"There's nothing AT about it. And repeating "it is decidedly NT or AT" doesn't make a blatantly original looking coin questionable or a blatantly AT coin other than AT."

 

 

 

Who said it did? Saying they are blatantly original or blatantly AT does not make them so, either.

 

They are opinions.

[MarkFeld]

"There's nothing AT about it. And repeating "it is decidedly NT or AT" doesn't make a blatantly original looking coin questionable or a blatantly AT coin other than AT."

 

 

 

Who said it did? Saying they are blatantly original or blatantly AT does not make them so, either.

 

They are opinions.

 

You are, of course, correct - they are opinions. But what is your point in repeating "it is decidedly NT or AT" - that no coin can be reasonably categorized as AT or NT?

[RWB]

The MCMVII looks fine to me. Spots are not objectionable....

 

The mint did several examinations of alloys over a period of years (See "From Mine to Mint" for one example) for the purpose of understanding segregation within the melt and within coinage ingots. All tests showed that gold-copper alloys were uniform; silver-copper were not necessarily uniform.

[Afterword]

"...that no coin can be fairly categorized as AT or NT?"

 

 

 

 

I would not say "no coin", as the history of a coin, if known, can sometimes provide adequate proof. If you buy a coin from a so-called "coin doctor", for instance.

 

 

 

"But what is your reason for repeating "it is decidedly NT or AT"..."

 

 

 

 

Ask yourself why you have repeatedly said that this coin or that coin is blatantly AT or NT, and you have your answer.

 

 

 

 

 

 

 

[MarkFeld]

"...that no coin can be fairly categorized as AT or NT?"

 

 

 

 

I would not say "no coin", as the history of a coin, if known, can sometimes provide adequate proof. If you buy a coin from a so-called "coin doctor", for instance.

 

 

 

"But what is your reason for repeating "it is decidedly NT or AT"..."

 

 

 

 

Ask yourself why you have repeatedly said that this coin or that coin is blatantly AT or NT, and you have your answer.

 

 

 

 

 

 

 

Thanks for the response.

 

I have made my referenced comment in a few instances. I was wondering if you were making yours in reference only to specific coins, as I did, or if it was meant to be a general comment.

[Afterword]

"I was wondering if you were making yours in reference only to specific coins, as I did, or if it was meant to be a general comment."

 

 

 

 

If I do not know the history of a coin and the subject of NT versus AT is involved, I am likely to make the comment you are referencing.

[coinman_23885]

The mint did several examinations of alloys over a period of years (See "From Mine to Mint" for one example) for the purpose of understanding segregation within the melt and within coinage ingots. All tests showed that gold-copper alloys were uniform; silver-copper were not necessarily uniform.

 

But you are effectively making a statistical argument about the larger population based on a small sample size. And while I agree that statistics can be used in this way to look at larger trends and the population generally, there will always be variation in any distribution and outliers will occur. Certainly, improper mixing to the degree of the Saint I posted would constitute a very tiny fragment of the population. (As I said, I have seen maybe half of a dozen at most). In the context of this thread, although I think copper spots are more common, in the grander scheme of things, I don't think these constitute a large portion of the gold coins struck. So I do think it would be within the bounds of possibility and plausibility.

 

Of course, this is merely opinion. My recommendation is to find a common date coin that doesn't trade for much if any premium over melt with copper spots and sacrifice it. If you ever conduct a metallurgical analysis, I do hope you publish your results either in a book, the JNR, or here.

 

P.S. Does anyone know if PCGS's "sniffer" would be of any use? How sensitive is it and could it detect the composition of copper spots? I hope one of the chemistry Ph.D. holders will chime in. If it can be done (so it wouldn't destroy the coin or toning), I would be willing to attempt to cross my Saint from NGC to PCGS under the Secure Plus tier (at my cost) to find out. I am not sure how much analysis that PCGS would give out though. It is worth finding out.

[coinman_23885]

Here is an example of how extreme the anti-copper spot attitudes get. Years ago I had this 1907 High Relief $20 gold on consignment. When I offered it for sale, a number of dealers rejected instantly because of the minor copper spotting on the bottom of the reverse around the area of the sun. This is a really beautiful example with fully original surfaces, and yet some very minor spotting in a area that was out of the focal point of the design put the coin on the reject list.

 

 

This coin was graded MS-64, and yes I can see why CAC would give its approval to a gold coin with minor copper spots. There is nothing wrong with them if they are light and do not detract from the eye appeal of the piece.

 

That is very sad to hear. I like the coin, and if I was in the market for one of these, I would have no problem with the piece you posted. It is gorgeous!

[Matt_dac]

Agreed - and I can't even see the spots from the picture.

[Nutmeg Coin]

I agree that that HR Saint has exceptional eye appeal with no problem copper spots. It is unfortunate that the knee jerk reaction to gold coins with minor copper spots is so critical. On type gold for years the main buyers would discount spotted coins significantly, and then where would you go with the coin? I bought two $20s today with spots one in the holder and one out, and I realized that because they are common dates for strictly economic reasons they needed to go through NCS for the cheap copper spot option. Years ago an 1866-s $5 Lib. no motto graded AU58 was offered to me at a discount, problem was it was seriously spotted, wart-like. A coin like that would need to go through spot removal to be marketable.

[RWB]

What I am fundamentally suggesting is this: The term "copper spot" was evidently applied because of the color of the spot, not its composition. I've found nothing that says anyone determined - or even tried to determine - what caused the discoloration.

 

I'm trying to get past the "circular argument" which is commonly used in numismatics to authenticate a claim. As the lady said in the old Wendy's hamburger commercial, "Where's the beef?"

[BrokCoinCollector]

Well I have an OXFORD XMET-5100 at work that test metals without destorying the metal. It will pick up anything in the "testing" area so I m sure it would pick up even the smallest trace amounts. If I ever get my hands on a gold coin I will have to give it a zap and see what comes up.

[RWB]

BCC-

 

Send me a PM with contact info. I can probably find a double eagle or eagle that can be tested.