All copper coins in circulation were blacks? Or dipped in oil?

Hey

As you know most copper coins in Antique and Middle Ages were made of copper. Copper is brown in color, but when it reacts with oxygen it will result in creating layer of black patina. (Or something like that)

My common sense is telling me that most of the copper coins circulating in Athens, Rome or Constantinople during the time of Pericles, Trajan or Justinian were black.

But i’ve also been told that copper coins are black because collectors dipped them in oil to make them more pretty/soft instead of crusty?

So, I want to ask:

(a) Do we know what color copper coins were when they were in circulation?

(b) Are copper coins black because of reaction with oxygen or because of dipping them in oil?

Thank you so much in case you can provide an answer.

 

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a)


b) No

 

Here pennies in various degree:

 

On this Pompei fresco you can see how Roman coins looked back then in the 1st c.
On the left there is a pile of denarii and aurei. On the right a pile of AE coins : copper asses and orichalcum dupondii and sestertii. The copper asses are reddish brown, like modern copper coins, and the orichalcum coins were yellow.

(I think there were no copper coins in Athens under Pericles, in the 5th c. BC. The Athenians only used silver coins).

 

Here’s a chart with 20 coins that are all copper. There are various shades due to toning of each color.

So the answer to your
a) question is Copper has different colors
and the answer to your question b) is a simple No.
Most of the ancient coin collectors have in their collections copper coins that, at a minimum, show a degree of red and we also have black coins. It’s just toning and that changes from one copper coin to the next. It all depends on the conditions the coin was under over the last 2000 to 2500 years or so.

 

This thread reminds me of a Justin II & Sophia follis which I bought 12 years ago. It's a SB_360 from the Constantinople mint; 566/567 A.D. The coloration of the patina in the image below is accurate.



In my communication with the highly reputable dealer who listed it, he wrote the below paragraph regarding the coin's "patina" (or near lack thereof). Note especially the portion which I made bold for emphasis, as I share the same view.

"There is no patina on this coin other than a very thin red toning in the recessed areas of the obverse and reverse, and some rather thick patina in the edge cracks. I don’t know of a natural process that would result in no patina on the surfaces and thick patina in the cracks (although that’s not saying that I know that there AREN’T any such processes). My best guess is that this coin was stripped of its patina, and the red toning is artificial (though quite pretty). I just think the coin is interesting because there is almost no corrosion damage, it is well and evenly struck, and it has less wear than is usually found, so it looks a lot like such a coin must have looked while actually in circulation in ancient times. Something like the thin red toning in the recesses on the obverse and reverse also probably would have been present on a coin in active circulation."