The colors of US gold coins

[RWB]

A post on PCGS reminded me that many collectors are unclear on why US gold coins seems to have different colors even when uncirculated and un-dipped.

 

There are really two sets of reasons: one involves the alloy and the other involves annealing.

 

Alloy –

Pure gold (1.000 fine) has no alloy and is a somewhat bright yellow color. If pure copper is added the color will darken and redden somewhat which is the common orange-gold color of most US gold coins. This was the gold color goal of the mint.

 

Pre Civil War refining techniques did not remove all impurities from either gold or copper. Each gold melt thus had a slightly different mix of gold and other elements commonly associated with native (mostly placer) gold. Silver was the most easily recognized impurity and the mint recognized that a small amount – up to 0.005 – could remain in the coinage alloy. Coins from Charlotte and Dahlonega usually contained silver up to this percentage. They also contained variable quantities of lead, tin, iron, antimony, silicon and assorted minerals. Silver could produce a greenish cast to gold if certain other conditions were met.

 

Copper, being more reactive than gold, was more difficult to refine to high purity, and the copper added to gold melts introduced additional trace impurities. At times, these impurities made the gold ingots brittle (commonly too much lead) and would force condemnation of entire melts. Variable alloys affected the other three pre Civil War mints, also, but the effects were less pronounced because of better quality control and larger quantities of metal processed.

 

Post Civil War refining was more consistent and the color of gold coins was also more consistent. By this time, the source of gold had no effect on the color of coins. When electrolytic refining became the standard, any alloy variations were intentional not circumstantial.

 

Annealing –

Gasses in the annealing furnaces combined with copper (and other elements) in the planchets and created reddish to blue-purple surfaces on some planchets. After annealing, a brief nitric acid dip removed most of the discoloration, but it also left chemically active copper in place of copper compounds. When the mints changed to methane gas annealing furnaces in about 1902, the final color of gold planchets stabilized, but the copper atoms were still subject to combining with gasses in the production areas.

 

[coinman_23885]

What process or which impurities in the alloy do you think caused this toning pattern?

 

[jom]

I had this one at one time...similar to coinman's:

 

 

I also had this one...violet toned $2.5 Indian:

 

 

I've always wondered how this could be. I've been told that the latter was AT...used a hot plate or some such. It was PCGS certified, BTW.

 

jom

[coinman_23885]

I would love to have owned that Saint Jom.

[yonico]

Wow great post!! Very interesting..

And great coins, especially Jom's st. Gaudens.

[BillJones]

I have not been able to photograph the exact color of this 1857-C gold dollar, but this does show the odd gray toning that is in the fields. The gold dollars from the Charlotte mint in the late 1850s have been grouped as among the worst made coins ever produced by the United States mint system. This piece obviously has something in the mix in addition to copper and gold, and this is not the only example that I have seen of this general appearance.

 

 

And here is another view of the coin under different light. Neither of these photos are an exact view of the coin when you see it in person.

 

[RWB]

Toning and the color of coin gold are two different subjects.

 

Non-destructive scans of gold from the GA and NC mints should indicate the surface composition including many impurities. The alloy likely will vary across the coin’s surface. All that has been done so far is to make rough guesses based on contemporary assays and guesses. It would be helpful if someone would fund the non-destructive testing of all GA and NC gold. Then, there would be the possibility of establishing a correlation between color and alloy.

 

Gold does not react with most other elements, thus it does not tone. What creates the color are chemical reactions with the copper (and occasionally silver) alloy and with impurities. Surface toning also comes from chemical changes to surface contaminants such as traces of lubricants, human breath deposits, bag dust, etc. (Note: Planchets were routinely given a very thin coat of oil to prevent sticking in the press feeder. No attempt was made to remove this after striking. Also, the old toggle-type presses had many open lubrication points and were thus surrounded by a tenuous “fog” of oil/moisture mix.)

 

[jom]

I would love to have owned that Saint Jom.

 

I always thought the Indian was prettier. The $20 was just "OK"...maybe MS64. I showed it around and no one really cared about that odd toning. I think I sold it for what I bought it for.

 

Now I think it would make a big splash for whatever reason...I've now seen a few photos of similar toning such as yours. Odd that both of ours are 1924...

 

Here's an "orange" $10 Indian I owned:

 

 

Thanks for the info RWB!

 

jom

[Hard Times]

Roger is correct,

Gold is inert and does not bond, it is one of the noble metals, known as noble because it doe not fraternize (bond) with other elements. Noble metals also include osmium, iridium, ruthenium, rhodium, platinum, and palladium, which these six together are called the platinum group elements (PGE). Not only are these metals noble and generally found as metal alloys in nature under most conditions, they as you know are also very rare. This is because when the Earth formed, the noble metals, rhenium, silver, and some other transitional series elements, had a very strong affinity for being 'noble', not bonding with the oxides and silicates that were formed in the mantle and the crust, and instead went with iron when the Earth's iron-rich core formed. We estimate that about 99% of all of these metals in Earth are in our core, hence their rarity and why we value them so much. In reality, we have an overabundance of gold and PGE in the mantle and crustal portions of Earth than expected from iron-rich core separation, and the reason for that has been heavily debated for 3 decades and still not resolved.......

Roger is correct that the toning comes from the copper, and sometimes silver and others, in the gold that will bond with sulfur and oxygen. Most oxides are black, like when we see silver coins tone to when extreme. Some copper sulfides have the gold-red-blue-violet colors that we see in beautifully toned gold and silver.

Interestingly, many of the Carson City Gold coins are more rich in silver than say those from Philadelphia minted at the same time. This is probably because much of this gold came from the silver-rich ores of the Comstock Lode in Nevada and probably stayed in to the gold to more of a degree when refined.

I had no idea that we don't really have a good statistical study of the minor and trace element compositions of US gold. I would love to take up Roger's challenge to measure them, it would take time and some costs to pay for for the analytical time. I would need a good sampling of gold coins also.

 

Best, HT

 

 

 

 

[Hard Times]

The orange-gold toning is fairly accurate on this one, a popular overstrike mintmark from Dahlonega.

 

 

Best, HT

[mkman123]

great post and love the gold in here!

[Nutmeg Coin]

Thanks, RWB for a great thread and topic!

 

One of my nice toned gold coins:

 

http://www.teletrade.com/coins/lot.asp?auction=1250&lot=1960

 

Since it was minted before 1800, the gold was probably from one of the existing colonies.

 

One coin with AT that I bought and successfully had conserved:

 

http://www.teletrade.com/coins/lot.asp?auction=3306&lot=1963#n

 

In hand that $2 1/2 was violet technicolor.

[lehigh96]

Gotta love toned gold coins!

 

[jom]

I KNEW I had seen yet another 1924 Saint like that. Maybe it was something in the mix of the copper/gold that year...

 

jom

[coinman_23885]

Gotta love toned gold coins!

 

 

Gorgeous Lehigh; is this your coin?

[coinman_23885]

I KNEW I had seen yet another 1924 Saint like that. Maybe it was something in the mix of the copper/gold that year...

 

jom

 

Jom, I wonder the same thing. Maybe RWB has some information on how the planchets were prepared this year. I think Lloyd from ATS also had a 1924 in an old no line fatty that had rainbow colors and was very similar to yours (in terms of the pastel colors).

 

Toning and the color of coin gold are two different subjects.

 

I know, and I hope I didn't take this thread away from what you had originally intended it to be, but the alloy and the way it is mixed fit perfectly with the questions that I have had about the gold toned coins that appeared in this thread. I would love any thoughts that you might have. 1924 seems to be an interesting year for toned coins, and I am curious if there was an special treatment of the planchets, etc. As always, your insights from your research are appreciated.

 

P.S. The multicolor toning appears to be more common on the St. Gauden's Double Eagles only, and I have seen four or five of them like this, and only a couple of other dates with only a specimen or two. I know the same size is small, but I still think there might be something here.

[Nutmeg Coin]

There are those who say there is nothing you can do for gold coins with light cleaning because gold is one of those elements (the only one?) that has no isotopes.

 

Actually because of the copper and other impurities it will tone. I have spoken with workers at coin companies who have left lightly cleaned (no grade) coins on sunny windowsills for extended periods of time and the coins toned nicely over the course of a couple of months. I had an MS63 $20 Lib. that when cracked out of its old holder (recommended by an "expert") no graded because of light cleaning. When left on the proverbial sunny windowsill, it graded 64!

[dimefreak]

This has been on my radar for a while. If/When it comes to Market ( Iv'e been told it unlikely) THe sparks will fly and I plan to be a strong bidder.

 

My equivalent of a 1913 V Nickel

[MarkFeld]

Thanks for that informative post, Roger.

 

Here are a couple of relatively colorful gold coins which I just placed with clients....

 

1904 $20 Liberty MS65

 

 

1924 Saint MS65

 

[RWB]

At present, I have found nothing to indicate that gold was handled differently in 1924 than in any other year. Each denomination was “operated on” separately, so what affected double eagles likely did not affect half eagles.

 

One thing that my current research on the 1942 experimental pieces has revealed is that nearly all of the "colors" we discuss for coins and entirely subjective. Two people will likely have different visual impressions of the same coin. This is fairly minor with metal coins, but the 1942 plastic pieces have traditionally been cataloged by color - yet with no standards at all.

 

(There are ways to prepare objective color measurements, but ti's way off the numismatic road.)