Anyone use one of these?

This is all about the moisture, which no one can doubt is problematic. But won't the surface only tone? And once everything that can tone does, what happens?

 

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Think of it like rust. It will keep up until all the interaction stops. What happens when everything that can tone does? It stops.

 

Does process continue below the surface, though? If it is caused by exposure to gases or moisture, would it not stop at or near the surface?

 

It gets to be a question of balance. If the emissions stay the same or lower, the surface reaction can stop. That is what happens in a lot of our coins, they toned because of the envelope or cabinet we put them in, an equilibrium gets established, and while in the same conditions the surface can remain stable.

Put the same coin in a situation of non-equilibrium, like a moist environment, and there can be continued pressure for it to continue to oxidize. In such an environment, the end game will always be the same, total destruction.

So, what has happened to the coin in the past is not what matters, its under what conditions you store it in the future that will dictate future damage/toning. I would say most toned coins will be stable in good coin storage conditions. Fresh silver or copper, though, even in "good' storage conditions will tone, they need near ideal conditions to not tone. However, ANY coin, no matter if toned of not, will tone or start toning again if placed in poor storage conditions, like a damp environment with a sulfur source. As long as they remain in those conditions, no equilibrium can be obtained, and it will result in damage and corrosion if left unchecked.

Btw, to answer your question Bill, the toning starts on the top surface layer, but as it approaches black and goes into corrosion, the reaction goes deeper and deeper into the metal. Eventually the whole coin would be the reaction, like a porous coin.

Like I said, what I will NEVER buy is a coin with matte black toning. You are almost positive the toning/corrosion has started to go deeper into the metal, and you have no idea how far.

 

Okay, I think I have eased my doubts. The trouble was that I have never seen anything in this terminal state. While the piece Doug linked to was no doubt a problem coin, it clearly hadn't reached the level of deep corrosion that Chris talked about in his last post. What Chris said about equilibrium provides an explanation for their apparent scarcity - the conditions either reach equilibrium and the process slows down, or additional environmental factors​ intervene and cause damage.

 

I hate to have to do it, but the terms "reactants, environment, and 'relatively' come into play. The surface of a coin forms a thin chemical layer ( generally called patina) which begins forming immediately after striking. If in a dry, low air sulfur reactants condition, and low acidity such as from atmosphere or environmental ( like woods, acid rain, pvc plasticizers, etc) could stay at that point for a long long time. Some ancient coins ( as you know) can develop such a stable patina, that it may even silica replace on the surface metal ( desert patina). That is one extreme.

The other extreme in this modern world is that for a coin so exposed, the reactants in the industrialized world tend to be high ( especially high sulfur oil and coal burning areas) , and moisture quite variable, that toning/tarnish/corrosion (whatever it is called) can continue deep into the surface from the dark gray-brown/black stage with visible pitting. I have done experiments exposing silver coins directly to H2S gas in a sealed container and 0.1 M equiv. will take it to black in a few days. But hopefully this level doesn't occur in someone's living area. Since the gas was generated by a method where water was present, moisture level was high.

I guess the real answer is , It can happen and continue, but it isn't necessary or a sure thing to occur. sorry.

 

Thanks! That is exactly the kind of answer I was looking for. If you ever have the time, I'd even be open to a more technical explanation.

 

Here is a quote to a thread over on the NGC forums about coins with terminal state toning being marketed as black widow Morgans. The members then took turns posting Morgan Dollars with terminal state toning.

Black Widow Morgans

Of course, most of the coins in that thread don't actually have terminal state toning, but there are a few really good examples.

 

That dark, even toning I have seen before, many times. It's a good indication of a coin that's been around a while. When I see an ancient or medieval coin with this color, I check the major collections of the type that sold in the 20's-60's. Ancient collectors positively adore this kind of thing. And if, as Desertgem suggests, it is stable, then that's even better.

 

Coins in space?

 

I follow that. But I don't get why someone would want to dip it away.

Very true. I guess my reasoning behind appreciating this "terminal state" of toning is that the more iridescent shades are prone to changing. Buy a rainbow toned coin today and next year you may have battleship gray. But with a dark "cabinet toning," as we call it in the ancient field, changes are much less drastic.

And as always, we find moisture to be the biggest problem.

 

Great link Paul, thanks. Most of these look fine of course. However, I would wager a nickel that if the coin at the top of page 2 were dipped, the owner would not be happy with what is underneath. Am I sure of it? Of course not. I just think that one went a hair too far, and I don't like how its turning matte.

 

Sometimes you must if you are going to preserve the coin. Having such thick, heavy toning is not the best thing to have in place if there is danger of the toning progressing. If you are borderline dangerously crossing over from toning to corrosion, if you dip the coin you can lessen the likelihood it will develop into corrosion. IOW, removing the toning layer will cause the coin to have to reform the toning layer again before corrosion can happen, so sometimes we have to dip to save the coin from damage.

Also, Bill you will be a little bit out of place if you are equating black toning on most ancients with this topic. Most ancients with black toning is an old, hard toning formed over centuries. It may be chemically similar to this issue, IDK, but I find ancient shiny black toning very stable and not susceptible to going into corrosion as modern black toning. I am with you, I LOVE dark toning, and with ancients I can relax about it and not worry as much since it is by its nature a more permanent toning than moderns have. If I ever saw a denari turn from colored to dark in my lifetime I would worry, and follow the same logic as we are discussing here. For ancients that have been black since they came out of the ground, I would not really worry about them. Remember, our ancients are tough coins, as opposed to these wimpy little modern ones.

 

Interesting you brought this up. In the last couple of decades, earth/satellite based sensors and research space probes, have generated many papers on chemical reactions that are occurring in space. Space seems to contain every natural element found on earth ( but of course much diluted per volume), so corrosion would be much slower relatively. But the energy levels from radiation much higher could offset some of that. So given enough time, I would expect some reaction with coin type metal in actual space environment ( not just riding in the satellite), but humans may not be around long enough to see the effects.

I think it would be interesting to find metal objects in the subsurface of the Martian desert. I would expect interesting patina.

 

With all the pollution in China these days, you have to wonder if they really have any NT coins vs. the usual AT caused by the foul air. Beijing is many many times worse than LA now.

 

Didn't NASA send up a 1909 VDB cent to calibrate instruments up there?

 

They did! One more to X off the population list.

 

Here is a scan of an example. Check out the reverse.