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How do you get copper/alloy spots on .999 gold coins?
drfish
Posts: 948 ✭✭✭✭
Especially when they"ve been in a slab the majority of their existance? Heres the info I found on Tax Free gold's site(thus the "british accent") -"Red spot can occur on almost any gold coin, it certainly happens on 22 carat gold coins. We have never seen it on .999(9) fine gold coins, and presume it is virtually impossible for it to occur on fine gold.
From our knowledge of metallurgy, we can tell you that when gold is alloyed, usually with copper or copper and silver, the alloying is obviously done in the molten state, and then has to cool. During cooling, crystalisation occurs, the crystal forming around "seeds" which are molecules of the elemental metals. There is a slight tendency for the elements with the highest melting point to start to crystalise first, and this can lead to small localised areas with slightly higher or lower concentrations of the constituent elements. In ternary alloys (three elements) three pairs of binary (two elements) alloys can also form. These areas of variable alloy are usually of microscopic proportion, but can sometimes be large enough to be visually discernable.Copper oxidises and forms other salts fairly readily whereas gold is almost completely inert, and silver lies in between, although it is fairly unreactive. This means that if some parts of the alloy are copper rich, and are exposed on the surface of the coin, then it is possible for these parts to exhibit toning or tarnishing. The red spots are areas with a higher copper content, and as copper is a red coloured metal, this shows itself in an area which is less yellow and more red than the rest of the coin. If this area subsequently tarnishes, it would almost certainly go towards a deeper red or brown colour. Whenever we have seen red spot, it has always been an area about the size of a pinhead, sometimes with more than one spot on a coin".......Heres a snippet from NGC's site - "the American Buffalo coins and most foreign bullion pieces are of nearly pure gold and will not spot under normal circumstances." These were the only refences I could find to copper spots on .999 gold.So how does an alloy of .001 lead to copper spots/streaks visible to the naked eye?I've only seen it once on a 07 Spouse coin and I've looked at probably a thousand images online.How common is it and how does it happen?
From our knowledge of metallurgy, we can tell you that when gold is alloyed, usually with copper or copper and silver, the alloying is obviously done in the molten state, and then has to cool. During cooling, crystalisation occurs, the crystal forming around "seeds" which are molecules of the elemental metals. There is a slight tendency for the elements with the highest melting point to start to crystalise first, and this can lead to small localised areas with slightly higher or lower concentrations of the constituent elements. In ternary alloys (three elements) three pairs of binary (two elements) alloys can also form. These areas of variable alloy are usually of microscopic proportion, but can sometimes be large enough to be visually discernable.Copper oxidises and forms other salts fairly readily whereas gold is almost completely inert, and silver lies in between, although it is fairly unreactive. This means that if some parts of the alloy are copper rich, and are exposed on the surface of the coin, then it is possible for these parts to exhibit toning or tarnishing. The red spots are areas with a higher copper content, and as copper is a red coloured metal, this shows itself in an area which is less yellow and more red than the rest of the coin. If this area subsequently tarnishes, it would almost certainly go towards a deeper red or brown colour. Whenever we have seen red spot, it has always been an area about the size of a pinhead, sometimes with more than one spot on a coin".......Heres a snippet from NGC's site - "the American Buffalo coins and most foreign bullion pieces are of nearly pure gold and will not spot under normal circumstances." These were the only refences I could find to copper spots on .999 gold.So how does an alloy of .001 lead to copper spots/streaks visible to the naked eye?I've only seen it once on a 07 Spouse coin and I've looked at probably a thousand images online.How common is it and how does it happen?
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I don't think spotting it is very common however it does happen from what I see. Also I am pretty sure the amount needed to spot a coin is very tiny, they have looked with electron microscopes to see the cause of it and it is other elements in the gold beyond the gold itself.
<< <i>Could it also be the .001? Gold is out of my price range, so I have no first hand knowledge >>
That would be 0.0001 for the 0.9999 gold.
Red spots were very prevalent in the first couple of years. The mint was even surprised and couldn't figure it out.
President, Racine Numismatic Society 2013-2014; Variety Resource Dimes; See 6/8/12 CDN for my article on Winged Liberty Dimes; Ebay
Regarding the streaking, perhaps it is possible some surface alloy was rolled into a thin streak itself?