uncleaned coins - before and after

With a good, proper conservation, there need not be any residue or encrustation on an ancient coin.

Here is a Caracalla denarius from a London private collection I now own. This coin shows no signs of damage or wear, but I can 100% guarantee that this coin was underground for 2000 years.

 

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I can still see some residual traces of patina (although cleaned) on your coin, but the one I posted has no traces of cleaning whatsoever.

 

...But Sometimes, in a real hoard, the coins can be packed together so tightly that the environmental effects can be minimal. ...Right? I've seen that from pictures of recent hoards on the BBC website. ...What am I missing?
...Granted, at the commercial level, cleaning is all over the map. Including examples that just instantly scream, "Cleaned!"

 

My point is, that it is physically and chemically impossible for silver to NOT tarnish.
In the presence of any amount of oxygen, silver metal engages in a spontaneous oxidation reaction of something like
Ag + O -> AgO

Here's an example of a professionally conserved gold coin. When done correctly, you can not even tell it was cleaned.

 

The only possible way that silver would not oxidize is if it was either
a) hermetically sealed in a vacuum chamber with NO oxygen whatsoever
b) buried in the anoxic mud in the bottom of the Black Sea

In no situation will a jar of coins dug out of the ground have coins that have ZERO environmental damage or oxidation.

 

Thanks, hotwheelsearl, for the scientific reality check! ...Scientifically illiterate as I am, people who know what they're talking about (in any context) are unfailingly preferable to ones who don't.

 

Haha, I ain't no chemist, though I back in the day I was accepted to UC Berkeley as a Chemistry Major.

 

Well, that's good enough to impress one of us....

 

...Back to the Black Sea, are those ancient, surreally preserved ships a Thing, or What? Hope the marine archaeology (sorry, I just like that spelling) is ongoing.

 

So how about the coin I posted? I see no oxidization on it ? It cant be fake as it is in British Museum.

 

It's not fake, it was just subject to a VERY careful and professional cleaning.

Please refer to the gold coin I posted above - when someone very skilled in cleaning treats a coin, it becomes good as new.

 

Perhaps it never was or was sealed in some kind of container.

 

Yea that's what I also think that maybe it was preserved over the ground in some sort of container as you say.

 

Perhaps you should say "conservation" rather than "cleaning".

 

I am still unconvinced that any coin 2000 years old could have avoided all traces of oxidation.

I mean, look at American 90%, or even 40% silver coins from the last 60 years. The vast majority of those coins exhibit some level of oxidation.

It's incredibly inconceivable to me that 2000 years of various environmental conditions could ever lead to high-purity silver coin with NO oxidation whatsoever.

As I stated in an above comment, the oxidation of Ag with O is a spontaneous reaction and will occur, no matter what if there is even a tiny bit of oxygen in the environment.

Any coin in a vessel and underground is surrounded by soil, dirt, or other materials that are porous - they let oxygen through.

You see, even if you sealed a coin in a hermetically sealed jar, unless it was vacuum-sealed there would be enough residual oxygen in the jar to produce some level of oxidation.

TLDR: it's probably chemically impossible for a 2000 year old coin to have never experienced oxidation.

 

Correct, although when it comes to Ancient coins its somewhat of a potato-potahtoe situation...

 

Even if it were a Helman's Mayonaise jar and it was stored on Funk and Wagnall's Porch...

 

Kind of reminds me of the old saw of Aeronautical Engineers explaining why bumble bees can't fly.

 

I get your point, but I think we have enough evidence of tarnishing silver that we can reasonably assume that if I can't even keep my silver spoon clean for 2 weeks, that the ground can't keep silver coin clean for 2 millenia.

 

But we would expect at least see some trace of original patina no? Even if its clean them very carefully, I would expect in the devices or areas that is hard to reach to see some patina left. But the coin I posted has no patina at all in protected areas