Author Topic: PCGS or NGC? Slabbed or original packaging?  (Read 6329 times)

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Offline badon

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Re: PCGS or NGC? Slabbed or original packaging?
« Reply #15 on: August 01, 2011, 12:05:24 AM »
No, the research says it's silver and sulfur:

http://www.sciencedirect.com/science/article/pii/S1001052107600308

100 PPM is not .999 gold (3 nines), it is .9999 gold (4 nines).

I don't think there's much value in the comparison with the visual characteristics of water of similar purities, since you have to look through many millimeters of transparent .9999 water before you notice the cloudiness. Since gold is completely opaque, you don't get to see that much of it - in fact, you only get to see the top few hundred atoms thickness, where you probably will not notice ANY impurities, even in .9 gold (1 nine) or even much less.

True copper spots tone dark red, then brown, but never bright red like the red spots on "pure" gold coinage.

Coinslinger

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Re: PCGS or NGC? Slabbed or original packaging?
« Reply #16 on: October 13, 2011, 06:07:06 AM »
The cause of 'Red Spots' is neither Silver or Copper.... It's Sulphur.  And it can happen to any coin or bar no matter how pure the fineness.

Offline badon

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Re: PCGS or NGC? Slabbed or original packaging?
« Reply #17 on: October 15, 2011, 10:34:46 PM »
It's silver reacting with sulphur to produce silver sulfide, which is black in color. I assume the black color diluted with the golden color of gold produces the reddish copper color we see with red spots on gold. Of course, the color could be produced more complicated ways, but I don't think those are relevant in this case.

http://en.wikipedia.org/wiki/Silver_sulfide

Gold can react directly with sulphur to produce gold sulfide, but that only occurs in specific circumstances that usually involve the presence of silver.

http://en.wikipedia.org/wiki/Gold(I)_sulfide

If you have info about the red spots being gold sulfide instead of silver sulfide, I would be curious to read it.

Offline poconopenn

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Re: PCGS or NGC? Slabbed or original packaging?
« Reply #18 on: October 16, 2011, 01:14:07 AM »
Cuprous oxide is red color, cuprous sulfide is grayish blue and silver sulfide is dark gray. This is the reason that morgan dollar (90% silver, 10 % copper) can generate nice rainbow toning. It is a well establish fact that red spot is caused by copper impurity in the gold coin. When the storage place does not have sulfur, it will have a red spot. If trace of sulfur in the air, the spot will be brownish red or redish brown.