Cause of Red Spots on Gold Coins

https://kb.osu.edu/dspace/bitstream/1811/3687/1/V49N02_073.pdf

Is a good article on ancient gold purity. It shows that Romans were able to maintain .99 for a considerable time from different sources. This was a great feat, and something that they should be praised for, but its not .9999 or 1.000. Even gold nuggets aren't pure gold, as this article shows. A few pages in it shows gold content of many ancient coins, the best are always .99.

Doug, I was not disagreeing that gold cannot tone, I just don't know. I am just saying 1.000 is impossible, especially for something as common as metal for coins.

 

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why many silver quarter proof set tone into red or partly red on obverse and not on reverse?. is it because of the red color cardboard that hold those silver coins?. why not tone into other color?. anyone?.

 

which one is better?. pliable mylar, clear acrylic, or polystyrene?. i use cellophane to cover the capsule. it works.

 

Well the article I linked showed natural nuggets in their test sample ranged from 86.8 to 99% pure gold. Not completely "purified by nature". I have read how you purify by lead as well as mercury. I have purified gold myself using mercury on gold dust. If you read further about mercury refining it will show you that it is not completely purifying the gold, traces of other metals remain, as well as the mercury itself. In nature, yes, gold is found more pure than most other things. BUT, the first coins were electrum because that is the natural form gold was found in there, and its extremely common for silver to be found with gold found in nature.

I do not think we should take Pliny's word as to the scientific correct purification levels of gold they could achieve. We have it already, with the article posted, stating they were able to achieve .99 pure for coins they intended to be pure gold. It was quite an accomplishment, but not .9999 let alone 1.000.

 

If anyone else is as fascinated by ancient gold refining as I am, some additional things to look at are "gold parting" and "cementation". Silver apparently stays with the gold after cupellation.

For an irrelevant comparison, steel at the time was a hit-or-miss proposition that depended on which mine you got the ore from.

Does anyone know whether silver dissolves in gold like sugar in water, or whether the alloy is a mixture that might not be uniform? A microscopic spot of concentrated silver would be more reactive than the surrounding gold in that case, and would create a visible nonuniformity. That would fit the observation of silver in the spots.

 

please help me this one. what are the causes of those red spots on the silver quarter proof sets. see next for pictures.

 

please help me this one. what are the causes of those red spots on the silver quarter proof sets. if it was toned. why only red color. not other colors like rainbow. where it might be the red cardboard beside it?.

 

dont take my word for it go to your nearest jeweler and ask him to make you pure gold ornaments and see what he says

 

if you cannot get its pure form how can u say that the coin is pure gold and then how can you say pure gold tones?

pure gold has been attained in labs not in mints so we know pure gold does not tone ask any scientist and they will tell you pure gold does not tone and .99 gold is not pure gold but if you refuse to believe that then there is hardly anything anyone can say to change your mind.

 

...From the original post on this thread, which indicates the color spots are oxidized silver, not gold.

Can anyone present for us Good Science a la the OP, which shows chemical analysis of color on "pure" gold coins and reveals the color areas as ionic salts of gold ? I'm not saying they don't exist. I'm not saying anyone is "wrong". I'm just saying I am interested in seeing Good Science evidence.

The point has been made many times; color on gold coins of high purity can come from two sources, namely impurities IN the gold and impurities ON the gold. That is the basis of this thread; the color is due to oxidized silver, not gold - even though the gold was "pure" (which, of course, it isn't. Never has been.)

No one has demonstrated that color on a "pure" gold coin is from oxidized gold. Show me the science, a la the OP.

 

There are gases in the atmosphere other than nitrogen, oxygen, water vapor, argon and carbon dioxide, in trace amounts. Gold could conceivably react with one or more of them to darken over time even though it doesn't form stable oxides. EDIT: one of those links points to stable hydroxides: there are trace hydroxyl free radicals in the atmosphere (trace only because they're highly reactive). Could darkening be gold hydroxide? That's speculation. And it wouldn't explain red spots.

Relevant question: have there been any red spots on the .99999 maples? 10 ppm impurities is the lowest in coinage, at least that I've heard of.

 

Gold Hydroxide is a substance that is not found in gold deposits or any metal exposed to air. It is manufactured under nitrogen gas by precipitating gold hydroxide from boiling aqua regia ( must be a fun lab) with 3N Potassium hydroxide, and then several more boiling acid baths until product produced ( still under nitrogen gas). It is a yellow brown substance.

I think I was perhaos somewhat general when I said this in post #15

Gold does combine with other elements, but almost always under the extreme conditions not exposed to the air nor temperature/pressure of where you might store gold coins or whatever. I know of no boiling aqua regia naturally occurring on he surface of the earth in a pure nitrogen atmosphere.
Toning refers to a different color/appearance, and in this case it is "red" . So if the compounds mentioned in the OP are suspect, one must look for gold compounds that have a reddish color, and has a possibility of natural occurring. IMO.

Enjoying the thread.

Jim
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Oh come on. .9999 is labeled as so, because 100% pure is impossible. If 100% pure were possible, then why doesn't any mint make 100% pure bullion. Think about it, which mint wouldn't want to be the one to boast that their coins are 100% pure, while their competitions are only 99.99%. You don't think that they put the .001 of other metals in the final product to make the "alloy" more stable or to harden the "alloy." And who knows what the .001 other metal is? Is it copper, silver, nickel, plastic? 90% junk silver coins are listed as 90% silver 10% copper. I'd be a fool to think every single junk coin has exactly 90.000% silver and 10.000% copper and contains no other metal as in impurity. The whole notion is just ridiculous.

As for impurities toning the coin, I agree with the original analysis. The scientific methods used are very thorough. I've worked with an electron microscope and with X-ray spectroscopy and they tell you exactly what the material is in question. You might not think that .01% is much and shouldn't spoil the overall quality of the coin, but if a pot stew only had .01% rat crappola edited in it, would you still be willing to eat it? Or would .01% impurities of that nature be too much and spoil the whole product, even though .01% should be completely undetectable?

 

Like elements have a tendency to cling to like elements....this is the principle of adhesion. The .9999 pure gold is likely to be an alloy (mixture) of gold and other elements (silver). That means that every part of the gold has some impurity in it. The entire surface is going to contain "other element" that make up the .01%. You won't find the other .01% metal all clumped together in one spot, although spots of higher impurity concentration can exist due to adhesion. The article is saying that the spot are localized higher concentration of silver sulfide. I'd agree with the article as the methods they used to scan the metal are some of the most scientific we have to date. X-ray spectroscopy can tell you exactly what the metal in question is by the refractive and reflective properties of the object.

 

As for gold toning, I'm going to say that gold doesn't tone. But, I do think that the coin or metal would be a bit porous. All metals have a porousness of some degree, and absorb things like moisture from the atmosphere. Anyone who's work with vacuum systems knows that the metal vacuum vessel has to be baked out to boil out the moisture that fills these pores in the metal and ruins the vacuum. S

So, maybe when the ancient gold coin was freshly minted the original holder ate some fried chicken and got chicken grease imbedded into the metal. Then what you are seeing isn't the toning of the gold, but the discoloration of the chicken grease left behind by the handler.

 

Elaine, I've been purposely toning ASE's just to see what colors I can achieve. I've noticed that the coins tone a red color before changing and turning a darker shade (a bluish tinge).