Featured The Beauty of Impermanence

This might be malachite on soter megas

 

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It likely is. Bronze is comprised primarily of copper, with a small amount of tin. Malachite is an oxide of copper, as is azurite and cuprite. Silver also oxidizes. Over everyday objects we call this process tarnish. If left to progress over an extended period, it can become patina.

It appears that your coin was cleaned at some point, so the green oxide deposits might have developed subsequent to that. The rest of the coin, at least on the one side shown, is toning brown.

 

If I could get a smooth even layer of malachite over the entire coin that would be cool

 

Perhaps it might, but the whole process of oxidation is fickle and subject to conditions such as humidity and the environment (such as soil properties for buried coins) that a coin is stored or deposited.

Those magnificent, hard green patinas that some ancient coins display did not happen over night. Just look at a penny, and it is easy to see the progression from mint state red, to yellow to brown, and you get an idea of how, over time, a bronze coin (and silver as well) can change.

Perhaps, in a few hundred years your coin might be uniformly green, or brown with green, or who knows? The main thing, though, is to appreciate the coin as it currently is, warts and all. After all that's the fun, exploration and fulfillment of collecting ancient and other coins.

 

Would this also be malachite?

 

I really like your sestertius - just a wonderful coin.

The green deposits are probably malachite. Here is the formula and definition from Sciencedirect.com:

"Malachite is the another copper carbonate hydroxide mineral with chemical formula [Cu2CO3(OH)2] formed by the weathering of copper orebodies in the vicinity. The color is bright green with light green streak."

The surface of the coin undergoes chemical alternation over time. This is true for all metals, with the exception of gold. Copper is very reactive to oxygen, and that is why it darkens rather quickly. Add water, either directly through the soil, or in the form of moisture in the air (or both), and the conditions are present to create carbonate deposits that ultimately, under ideal conditions, create a beautiful patina.

Other factors, though can alter the process, creating corrosion and pitting. This is the old Rowan and Martin's Laugh-in of the 1960s "Fickle Finger of Fate" which applies to coins and just about everything else for that matter.

Your coin is a wonderful example as it is.

 

This thread as turned into a wonderful love-letter to Malachite in all its forms! But why not show some other minerals equally deserving of our attention? A bit of azurite has already made its way into this thread and I must say it is my favourite kind of patina! @TypeCoin971793 and @posnerfan_48 always tease me with my everlasting quest for blue patinas…

Malachite and azurite are both copper carbonate minerals and whichever forms depends on the partial pressure of CO2 in the environment; azurite only forms when extremely high amounts of dissolved Co2 is present, Malachite under more common but still carbonated circumstances. Plus azurite can also morph back into malachite once conditions change and are no longer suitable for azurite formation. That’s why true and almost wholly azurite patinas are so rare and when you do see both malachite and azurite on one coin, an earlier phase of malachite, subsequently followed by a phase of azurite is more common. So, store your blue patinas well! (Not in a glass of water please )! My absolute favourite blue-boy:





And in the last Steve Album auction, I bought these two:





Plenty of blue, but what gives these their characteristic two-tone, blue-beige/pink patina that I dig (what the Chinese sometimes call ‘Beijing patina’) is a relatively thin film of cerussite impregnated with moderately fine cuprite crystals. Early Chinese coins, especially spades, are quite high in lead content (cerussite is a lead carbonate), generally higher than their contemporary Greek and Roman counterparts, which is why you rarely encounter it thereon. Both of these spades, but especially the second one, also show something else you often see on Chinese spades: cementation copper! Patches of what seem to be perfectly fine bare copper over the layer of corrosion products. This is happens when in a reducing environment all oxygen is incorporated in other corrosion products. Cuprite from one coin can than precipitate on the other in the form of pure Cu (+CO2).



You can also see both the cerussite/cuprite and the cementation on this recent purchase. The coin was tightly packed with its neighbours, leading to little malachite and azurite formation. This did allow the cuprite-crystals to grow enourmous! You can easily make them out without magnification, especially on the reverse.

Or how about a less-easy to find (and spot) lead product? We’ve seen cerussite, but not yet the lead-oxide Minium (the orange-reddish deposits):



And to close: a fake patina on a fake Mac coin that at first glance, even under magnification, looks quite realistic!

 

@robinjojo thank you for your words and explanation.
The Antoninus Pius coin is "just" a dupondius, not a sestertius, in about 9 hours I will see it in hand

An interesting patina/shades/deposit on this Faustina as (or dupondius?!)


And probably the most valuable coin I have in my collection, Trajan quadrans RIC 693 (not many examples known), with some black deposits I have no idea about, especially on the reverse.
I do not want to clean it as it would be a shame to ruin it.

 

Yes, my mistake. I missed the pointed crown on Pius's head.

 

Totally understandable due to its condition. Also I didn't post the size/weight - 27 mm 12 g.

 

I just received a coin that I think fits very nicely into this thread.

It is a post-reform follis of Diocletian, 308 AD, abdication. What makes this coin exceptional is the patina, which is a blue-green.

I am providing two images of the coin: one in filtered sun light (through my skylight), and the other with the aid of a flash.

Roman Empire, 308 AD
AE follis, post-reform
Diocletian
Antioch
Obverse: DN DIOCLETIANO FELICISSIMO SENA VG, Diocletian, facing right, in imperial dress, holding a mappa and olive branch.
Reverse: PROVIDENTIA DEORVM QVIES AVGG, Providentia, left, facing Quies right, who is holding an olive branch and a scepter, Z (officina) below, ANT in exergue.
RIC #?
10.5 grams
27 mm, 6 h.

With the flash:



With only filtered light:



Van Meter makes the observation that "Quies is the personification of rest and retirement..."

You can see that the flash make the coin appear more blue, almost a turquoise blue, compared to filtered light.

Does anyone have the RIC# for this coin?

Thanks

 

What an interesting thread, @robinjojo

I’ve been buying several budget bronze coins that have interesting colors that make me a little nervous. This coin from Odessus, Thrace, has orange, hard and glossy parts. Does it look stable to you, or should I do something?

 

The patina, to me, looks fine. If someone tries to fake patina, it is pretty obvious. The fake patinas are usually achieved by applying a chemical, such as a very diluted acid, to create very superficial, kind of powdery or grainy green areas on the coin. Sulfur is another chemical used, but for bronze, it darkens the surface of bare metal to varying shades of brown.

Your coin clearly shows thick areas of oxides that can only occur over a very long period. Nice colors!

 

As far as stability is concerned, I don't see any problem areas on the coin.

The great scourge of ancient bronzes, and even more recent bronzes, is bronze disease, which manifests itself as very light green powdery spots on the surface, often covering further damage underneath. That condition requires treatment, that has been discussed extensively on CT. Left untreated the corrosive process will only get worse, but I don't think you need to worry about that with this coin, based on the image.

 

That is reassuring, thank you. It’s only a 17 € coin, but I think it is a very nice 17 € coin.

 

Impermanence was the subject on my Wabi-Sabi page. These were coins that gained some interest through things that happened to them that may or may not have been positive. This is not limited to patina but that certainly is one of the big ones.
http://www.forumancientcoins.com/dougsmith/wabisabi.html

 

Hi Doug

Yes, I have read your interesting and informative article a couple of times.

When I was young (Jethro Tull?) I was only interested in mint state Morgan dollars. My collecting universe revolved pretty much around collecting Morgan dollars based on VAM variety. That all changed when I saw my first 8 reales cob at the local coin shop that, by the way, was promoting Wayne Miller's book on Morgan dollars.

I found the cob fascinating both for its historical interest and its sheer crudity. The coin was the antithesis of everything Morgan. It had the appearance of having been made in someone's garage. But then, that was its main selling point to me: it was saying, in effect, "this is me, I am unique, and I am not from the US mint."

Over the ensuing years I sold off the Morgans, actually rather quickly and moved almost simultaneously into ancient and world coins. Now, over the past few years the focus is on ancients, for all of the wonderful diversity, history and artistry.

While this thread looks at the chemical aspects of impermanence, and how this process manifests itself in the coins we collect, I think that I have been a adherent of Wabi Sabi for all these years without even being aware of it.

Here's a coin that is not everyone's cup of tea, but one that I like not only for its execution and modeling, but also for the effects that time has had on it:

Celts in Western Asia Minor
Galatia
3rd-2nd centuries BC
AR Tetradrachm
In the name and types of Alexander III of Macedon.
Head of Herakles right, wearing lion skin headdress / Zeus Aëtophoros seated left; in left field, lion skin draped over club. Price 4058. 15.99g, 23mm, 11h.
Rare.

 

Robin-
Really enjoyed your post--- I myself like Morgans, but I also have gotten interested in foreign and especially ancients. For the same reasons as you--- and you explain it very well, my friend.

 

Thanks

Every now and then I write something that makes sense. But I do like to wax on about the beauty and poetry of ancient coins.