Cause of Red Spots on Gold Coins

now. are those toned worth anything or just a waste?.

 

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As for researching ancient smelting techniques, the only book I have covering it is "King Croesus' Gold, Excavations at Sardis". It refers to the technique used at the mint of the first coins. They did have small droplets of gold recovered that they claimed were pure gold, but this was in very small quantities, (think tiniest droplet). For the coins, the "pure gold" coins were all in the 98-99% range, using scanning electron microscope as the measuring instrument. Basically it shows in tiny quantities ancients achieved pure gold, but it doesn't appear they could do so in large enough quantites for coin production. There is another publication measuring ancient greek coins and their fineness, but I do not have that volume. Maybe Doug Smith or someone else does. I read it years ago and I never saw anything over .99 if I remember correctly, usually less.

As for the controversy, I really could go either way. In inorganic chemistry I remember gold does not like to bond with other elements, but will do so under certain situations. I could see a naturally occuring situation where gold could tone, like Doug describes, but I would be hard pressed to think those situations occurred often. Maybe its a situation where most toning is due to impurites, but on some gold it is the actual gold that has toned. I know this doesn't help much, and I would love to see more test results of the actual surface layer on the gold coins analyzed, (but thanks a lot for the OP article), but until then I believe both could be possible.

 

One difference between laboratory results and coinage experience is that a hypothetical reaction with a glacially slow rate might never show up in a lab time frame but would be relevant for a 500-year-old gold coin. It would have to be something other than oxidation, of course. It would have to be some compound that's actually stable.

 

I couldn't access the full article as I didn't have subscription, so I do not know how they were produced. But the way it reads, one could not just go out and find the oxides in nature, they do have to be produced in a lab. Also in several of the readings you provided, they mention that the oxides rapidly revert to metallic gold in the presence of air. So how could they maintain themselves as a "tone" . If tone appeared at 10:30 and disappeared at 10:31, wouldn't it (1) be a great conversation topic on a coin forum, and we would have already heard much about it and (2) I haven't found a citation that describes the oxides as a color different from white/gray or gold.

I understand that gold coins can show a toning. However, I find that when a scientific study shows the redness to be related to silver and not gold, and when studies of gold compounds such as oxides are rare and transient, I still have to go with the OP. I suspect it is a good chance that if a 500 yr. old toned gold coin was tested the same way that silver or copper compounds will be the cause. I guess that is the way I was trained. Thanks for an engaging discussion.

Jim

 

it is simple GD the 0.001is what causes the change in the color

now that is explained i still dont think you will change your beliefs but at least there is a endearing quality in your posts

 

I rest my case GD and no i dont hold it against you as you are not a chemist. the way we wouldnt hold a coin grade over someone who was not into coins. so back to business we have to now convince you to reverse this toning market you created.

 

I hesitate to wander in here with my long-ago college chem background, but all the discussion is about gold while the original paper attributes red spots to a reaction of silver and sulfur. "Accelerated tarnish test of gold in an atmosphere containing sulfur compound proves that the similar phenomenon appears when a small amount of silver is present on the surface of gold. It can be concluded that the occurrence of tarnish stains is caused by the presence of Ag and S."

It seems crucial that collectors recognize that exposure to sulfur contaminants in the atmosphere (or most paper and cardboard) can alter a gold coin's appearance. I've used Air-Tite containers for a few years with satisfactory results. I wonder, what strategies others are using to keep air away from their coins?

Best wishes,
Peter Anthony
wwww.pandacollector.com

 

Things can be made absolutely pure, but they must be protected. For example, silicon technology can produce pure silicon crystals, but upon exposure to the atmosphere, the silicon begins reacting with the atmosphere. Same goes for the international kilogram.

Gold is made commercially pure by using electroplating. It still isn't EXACTLY completely pure, but it's close enough that you won't see any funny spots developing on it.

As others have pointed out, 1.000 gold is not pure. Look up "significant figures" to see why. The ultra short version is that .9999 gold is actually something like .99985, with the last nine being the result of rounding. To call something 1.000 gold is technically correct, but it only means that it's pure out to 4 significant figures. In other words, "1.000" means the same thing as ".9999".

Also, there are other ways of discoloring a metal besides a chemical "toning" reaction. The metal surface can adsorb (stuck on the surface) or absorb (soaked deep in side) other substances. Hydrogen gets into pretty much everything. However, adsorption and absorption usually do not make spots. Instead, they make a consistent, even change of some sort. Usually it's not visible as a color change, but instead it changes the hardness or, malleability, or ductility of a metal - or something like that.

I suspect most of the gold "toning" we can see with our bare eyes is actually just microscopic dirt adhered (adsorbed?) to the surface, which then gets old and "tones". I doubt that any of the natural atmospheric chemical reactions that gold is capable of would occur often enough for it to be visually apparent. If it were, you'd probably have to be more worried about the atmosphere dissolving your lungs.

The impurities in "pure" gold, however few they may be, may be concentrated in "spots" where JUST IN THAT SPOT, the purity of the gold might be only .5000. Overall, the gold is .9999, but in JUST ONE SPOT, there's a bit of something else. That's how you get spots in "pure" materials.

Unless the ancients used electroplating methods, they probably could not achieve equivalent methods of purity. It is actually possible that the ancients may have experimented with electroplating. Look up the Baghdad battery for an archeaological find of ancient electric battery technology sufficient for gold electroplating. If electroplating was done, it was very uncommon, which is why only one ancient battery has been discovered, as far as I know.

Spots should be no surprise to anyone, no matter how pure the gold is, if it's not kept in a vacuum chamber. The world is full of crap that can get into the gold while, or even after it's minted. It doesn't take much to make a colored spot. The residue from a fingerprint is far more than enough to do that, and nobody would argue that the fingerprint changes the purity of a gold coin. The impurities that give you spots on modern coins are in much smaller quantities than what comes from a fingerprint, just to give you some perspective.

 

Speculating here, but if there's some sort of equilibrium between gold oxide forming and gold oxide breaking down, over time that could change the surface, maybe.

 

The last time this topic came up I mentioned that my 2006 Proof AGB had a red spot on it. It never left it's OGP capsule but has a bright red spot deeper than krispys AGB in post #9. It's in the safe deposit box now but the next time I'm in there I get it out and try to photograph it clearly enough to show the spot. I don't think this is the .9999 gold toning but the .0001 metal mixed in. No matter what the cause is, I'm not very happy with this situation. I'd rather have a "perfect" coin.

Bruce

 

Just as an aside, ancients did electroplate extensively. There are literally hundreds of items surviving electroplated.

I agree with the rest of your post, though.

 

I guess I should have been more specific about what I meant by "ancient", since that could mean anything from the dinosaurs to your grandmother Yes, you're right, electroplating is quite old technology. It isn't as old as the oldest coins, but it's still old enough you could categorize it with other "ancient" things.

 

That equilibrium is exactly what prevents the gold "oxide" from completely consuming the entire coin. Equilibrium probably occurs before the reaction products can even cover the surface with a single layer of molecules. That single layer would be invisible. With less than that, you can bet that it would be hard to detect even with sophisticated scientific instruments, let alone with the eyes of the average non-scientist coin collector.

Others have already said it, but I'll repeat it just for completeness: The few gold molecules that may exist on a coin in natural air are so rare that they are of no practical importance to coin collectors. You definitely, absolutely, 100%, never, ever, could EVER possibly see them.

With that said, yes, your speculation is right. It WOULD change the surface, but not enough for anybody to notice. After a few hundred years, it might be detectable with an electron microscope though. The effect your talking about is the same as the "crystallization" effect of ancient silver coins. Basically, the silver doesn't so much crystallize (since it was always crystallized) as the crystallization becomes apparent as the impurities get dissolved away by the wind and water:

http://www.forumancientcoins.com/moonmoth/crystal_coins.html

With the impurities gone, all that's left is the silver crystal structure. If something similar happened to gold, which I'm sure does happen, then the textured remaining surface would have lots of microscopic nooks and crannies for invisible debris to collect. Enough of that debris, along with the changed texture of the coin, will make the coin surface less reflective, and thus, it will appear to be "toned".

Although gold doesn't have the same crystalline nature as silver does, which is why ancient gold coins don't suffer from "crystallization" problems, I'm sure the effect is there to a much smaller degree. It may or may not be visible, but I would be surprised if it weren't visible, since we can see red spots just fine.

Either way, I'm sure plain old fingerprints are much more likely to have a prominent "toning" effect than any of these more complicated processes.

 

this photo prove to be successful in preserving the silver coin from being tone. simple insert the coin to the whitman square palstic holder. and sealed it with the small cellophane bag. and tie it closely. after many 25 years. it maintained the silver good in very good condition. unlike the one i used airtite holder with black ring. after 25 years. it toned.

 

this one is toned.

 

It is Parthian and Sassanian. They have extensive amounts of items silver or gold plated, its also where they found a surviving battery and plans on how to make them. Not quite as old as coins, but till going back 2300 years or so. I didn't mean my grandmother's tea set.

On the issue of plating, the Romans did it a different way with their 3rd century "silver" coins, effectively sea water leeching their surfaces before striking to give the impression of silver. Different than electroplating, but still interesting.

 

this one is toned with airtitie holder and ring.