Author Topic: Red Spots on Gold Coins  (Read 5749 times)

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Offline PandaCollector

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Red Spots on Gold Coins
« on: September 02, 2010, 01:46:14 PM »
One of the mysteries of Chinese gold coins is, what are those awful red spots that often turn up on them? Some people call them copper spots as copper's nickname is the red metal and it's a natural impurity in gold. Copper is also traditionally mixed with gold to create a harder, more durable alloy. Now a trio of Chinese chemists have done a study of the red spots and found they are actually made up of compounds of silver and sulfur. The presence of silver isn’t surprising as it is often mixed in with gold in nature and may not be completely removed by refining.

Sulfur, though, is the contaminant that turns your old newspapers yellow. It’s also a component of smog, spewed from power plants that run on fuel oil or coal. In one of the researchers’ tests gold coins were exposed to a sulfur-laden atmosphere. The gas reacted with silver impurities on the coin’s surface to produce red spots.

This means that every effort should be taken to reduce the contact between gold coins and air, particularly polluted air (which seems to be nearly everywhere these days, doesn’t it?).

P.S. There is a lively discussion on this research at http://www.cointalk.com/t126202/. Unfortunately, from my perspective, it sidetracked into what fineness gold could be purified to in ancient times.

Offline badon

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Re: Red Spots on Gold Coins
« Reply #1 on: September 02, 2010, 03:51:06 PM »
No matter how many nines there are in the fineness specification of the gold, there are still impurities that can change colors. The impurities could be any element in the periodic table, but tend to be things that are commonly naturally occurring in gold, like copper, silver, etc, which then reacts to other elements in the surrounding environment, like sulphur, phosphorous, oxygen, chlorine, etc, to become dark or brightly colored marks on the coin surface.

Fortunately they're easy to remove without damaging the coin. NCS does it professionally, but many amateurs get good results from their own work. The usual solution is to take a blow torch to it and heat the coin until the spot disappears. I've never done it myself, since I prefer to let the pros at NCS handle it for valuable coins.

Offline rubio2507

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Re: Red Spots on Gold Coins
« Reply #2 on: September 02, 2010, 04:47:01 PM »

....
« Last Edit: October 15, 2012, 09:27:52 AM by rubio2507 »

Offline badon

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Re: Red Spots on Gold Coins
« Reply #3 on: September 02, 2010, 06:19:48 PM »
I would like to see a photo of your coin. Do you have any pictures to show us? I bet it's a very nice looking coin.

Offline shadowninja

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Re: Red Spots on Gold Coins
« Reply #4 on: November 02, 2010, 05:20:28 PM »
Fortunately they're easy to remove without damaging the coin. NCS does it professionally, but many amateurs get good results from their own work. The usual solution is to take a blow torch to it and heat the coin until the spot disappears. I've never done it myself, since I prefer to let the pros at NCS handle it for valuable coins.
« Last Edit: August 23, 2012, 07:38:30 PM by shadowninja »

Offline JimJam

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Re: Red Spots on Gold Coins
« Reply #5 on: April 19, 2011, 01:58:35 AM »
I like to keep my coins in plastic cases.  I have seen the off colors before on some Chinese pandas that my friend had.  A lot of gold coins have other alloys added to increase strength and make the coins easier to handle without damaging them.

Offline badon

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Re: Red Spots on Gold Coins
« Reply #6 on: April 19, 2011, 08:49:43 AM »
Not these gold coins. Do NOT handle your coins, EVER.

Leave them in the original holders, and let NCS remove them when you're ready to send them in for conservation and grading. They will remove the spots for you, without damaging the coins through improper handling. They are extremely fragile, and almost no one is expert enough to realize when they're damaging the coins, even professional dealers with 50+ years of experience.

I see this is your first post - welcome to our forum!

Offline moosician

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Re: Red Spots on Gold Coins
« Reply #7 on: March 09, 2016, 07:58:26 AM »
I have quite a handful of graded mcc gold coins (ngc/pcgs) that have developed red spots over time. Some spots are small and mild but some are strong. The spots were not there on the coins in their slabs when i bought them!
Not sure if this has anything to do with the hot and humid weather from where i live?

Guess the only way to remove the spots is to send them to NCS and have them reholdered (extra$$$) :(
If i keep them, assume it would be much harder to sell them compared to a spotless one in the same grade  :(

So, what would you do?

Offline Mirkkanen

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Re: Red Spots on Gold Coins
« Reply #8 on: March 09, 2016, 01:59:30 PM »
I have quite a handful of graded mcc gold coins (ngc/pcgs) that have developed red spots over time. Some spots are small and mild but some are strong. The spots were not there on the coins in their slabs when i bought them!
Not sure if this has anything to do with the hot and humid weather from where i live?

Guess the only way to remove the spots is to send them to NCS and have them reholdered (extra$$$) :(
If i keep them, assume it would be much harder to sell them compared to a spotless one in the same grade  :(

So, what would you do?

I just recently sent a key date 1/4 oz gold panda in to NCS and NGC for conservation that was slabbed a 69 by NGC but which had 7-10 small red spots all over the panda side. When I bought it, the coin was spotted (although the dealer (P.A., ahem ahem) did not disclose this to me). It is scheduled for re-grading either today or tomorrow. I think the entire process will cost me about $35-$50 bucks for that specific coin, which is a lot less than losing $200-$400 by selling at the price for the next grade lower.

If you have a trusted dealer or trading partner, they can send the coin in for you, or do it yourself with a large batch of coins.

If you keep your coins in Coin Armour bags, maybe this won't happen.


Offline KeepOnTrying!

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Re: Red Spots on Gold Coins
« Reply #9 on: March 09, 2016, 02:46:10 PM »
I have quite a handful of graded mcc gold coins (ngc/pcgs) that have developed red spots over time. Some spots are small and mild but some are strong. The spots were not there on the coins in their slabs when i bought them!
Not sure if this has anything to do with the hot and humid weather from where i live?

Guess the only way to remove the spots is to send them to NCS and have them reholdered (extra$$$) :(
If i keep them, assume it would be much harder to sell them compared to a spotless one in the same grade  :(

So, what would you do?

The information out there strongly supports a strong role for atmospheric pollutants and certain gases in the causation of coin surface degradation. Following conservation and re-slabbing aggressive protective measures include intercept archival bags as already mentioned above. The unit cost of the bags is a pittance when compared to their potential benefit and the cost of the coins they protect. Good luck!
KeepOnTrying and Never Give Up!
That lion is also after you!

Offline moosician

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Re: Red Spots on Gold Coins
« Reply #10 on: March 10, 2016, 05:25:21 AM »
Thanks guys! I'll try that :)