Cause of Red Spots on Gold Coins

I am not disagreeing with you Doug, just asking questions. Given the fact Spock pointed out that .999 or .9999 is recent, does anyone have any darkly toned .999 coins? You showed some wonderful coins, but they aren't pure gold. Refining technology at that age simply wasn't able to produce that fine of gold. Given that silver will tone black with age, would it be possible for a small inclusion of silver, (found naturally in gold), could cause gold coins to darken?

I have observed the same gold coins toning as you Doug. Maybe not as long, but for a long time. I am open to either idea really, that either age and environmental gases cause gold to tone, (gold is not completely inert, just mostly inert), or metal impurities impart the tone. I would just like to know. One picture stays in my mind, that of a newly dug up pot of Roman gold coins, and they were bright gold. Maybe atmospheric gases are the cause?

Chris

 

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Yes, it does make sense to me. That is exactly what the OP stated - it is Ag2S and Ag2SO4 which create the toning colors.

As the Good Science in the OP states, toning can come from small amounts of impurities. My hunch is the modern Pandas are purer than the medieval pieces (which are magnificent, I'll add).

Another explanation on the 500 year old gold is surface contact, including organic and non-organic sources, can contribute to color on the coin.

 

I would like to give a big Shout Out THANK YOU to DesertGem for the outstanding OP. :high5:

 

No, but a .999 fine Panda developed spots, as do Maple Leafs, Philharmonics, and AGEs. And First Lady coins, I suppose.

 

Agreed. Excellent Post Desert, thank you.

 

is that the toned gold or silver coin worth more?.

 

Good question.

We must distinguish between "toned" and "spotted". I would think spotted coins almost always bring less than non-spotted coins.

Toned coins, on the other hand, usually bring more.

However, bullion people - who are often investors more than numismatists - may prefer untoned or perhaps not care... or even notice, since they often treat buying and selling as a commodity and don't always check the coin(s) closely.

 

Ok, I will research it. I know the US didn't have any kind of capability like that for most of its history. You say that .9999 is doable for the last 2000 years, how come only a couple of mints can do it still today? Most bullion is .999.

I have never, ever, seen ancient coins have such purity levels, even of coins they meant to be pure gold. .99 maybe, not .9999. Are you saying the touchstone can differentiate between .99 and .9999? I thought touchstones could tell the difference between "pure" gold and about .9 or .95 gold or the like, not advanced degrees of fineness as we are talking.

I am all about reminding people of technologies ancients had, vending machines, batteries, electroplating, etc. I just find .9999 gold a stretch. Just because your book lists 1.000 does not mean it is correct to significant digits. Where is the book's metallurgical data coming from? The fact the mint meant for it to be 1.000? Hard to list that, isn't it, when no mint on planet earth with today's technology can achieve such a feat?

 

I didn't know that. Very interesting history lesson. But when you think about it, it makes sense that the money systems of the time would have required this ability to operate.

 

Do any ancients ever show the same kind of discoloration, namely red spots and splotches, as is showing up on contemporary bullion coins? That's a different animal from overall darkening.

 

I will tell you what its a flight of fantasy to believe that old coins were 100 % pure gold and to say that it was doable for 2000 years well that sure leaves me speechless. without scientific data one can say anything one likes one can even say the gold is 101 % like some of the smiths do here when it comes to testing we find they actually meant 51 %. People can believe whatever they want to believe. Pure gold cannot tone with anything that is found on earth. all the people involved with metallurgy are not fools. It is preposterous to think that as coin colletors we are the be all and end all of the metals.

all the points you have raised are valid ones

 

exactly event he buffaloes had the problem one year and that was due to process of finishing the coins. that cannot be used to say pure gold coins tone.

 

yes but what is forgotten as in any balancing system you measure pound to pound so if your measuring pound is contaminated so will your subject

case in point you bring one kilo of gold saying its pure so i pull out my 1 kilo counterbalance which due to technology limitations is also impure and viola we have a perfect match and everyone is happy.

what we are all forgetting is that pure gold is very soft and it would be impossible to coin it without mixing impurities into it. go to any jeweller and ask them if they will make you gold ornaments in 100 % gold and see what they say.

 

A kilo of pure gold perfectly balances a kilo of impure gold.

Or a kilo of pure lead.

Or a kilo of feathers.

A kilo of anything balances a kilo of anything else.

A kilo is a kilo is a kilo.

 

I will research it and get back to you Doug. The main point is it becomes the increasing difficulty in extracting the trace metals that naturally occur in gold. It is a geometric progression. Could ancients do .99, Yeah I would say so. .999 would be very difficult and most of the time not worth it. .9999 I believe would be impossible given their technology. It is extremely hard for modern science to achieve this cheaply. 1.000 is only possible if you round, even today. To say gold is truly pure, with not an atom of impurity, is almost impossible unless you want to pay a million dollars an ounce. You have to vaporize it, trap off the gases at different points, then cool and do it again.

Blending to 4 decimal places is easy, start with the same .99 gold, so the impurities are the same, and blend in your silver and you will have 4 decimal place accuracy. This is NOT the same as making .9999 gold, let alone 1.000 gold. So no, I do not believe Krause or Friedberg saying 1.000 gold. I would not believe a modern bullion coin saying 1.000 gold unless they admit they are rounding.

Btw 24 carat is called pure gold, but its just a convenient name. It means .99 or .999 gold effectively, gold that is as pure as economically feasible and not interntionally diluted.

 

Gold will combine with other elements to form compounds. Look it up in any inorganic chemistry book (unfortunately, mine are all packed away. Otherwise, I'd cite specific examples). The only elements that won't combine with others are the noble gases, and even then Xe is known to form compounds.
As far as purity, there is no known room temperature solid element that is perfectly pure. Yes, you can get 6 or 7 nines purity (99.9999 or 99.99999%) if you are willing to work hard enough (i.e., spend a lot of $$ getting those purity level). So IMO, even pure gold, when exposed to appropriate contaminants (e.g., sulfur) will tone at some point.