Dark Toning Examples: Acceptable vs. Avoid

As I focus more on type coins and looking at a lot more early 19th century type coins specifically I'm finding a lot more darkly toned ones and left wondering what type of dark toning should I avoid (where it's a risk to the coin itself or terminal) vs. what is just nice original darker toning.

So was hoping people could post examples of older silver type coins with dark toning that they would both avoid as well as not worry about.

Here was one I came across. I assume this is fine but would this cause anyone hesitation?

 

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Toning is the exact opposite of a "risk" to a coin - it's a protective coating whose purpose is to prevent further damage. Copper and silver will both only acquire patina to a certain point - copper being full green or very dark brown, depending on the process, and silver becoming completely black. It doesn't progress from there.

Beyond that, all judgments regarding toning are subjective. One of my alltime favorite coins was pretty much terminally-toned:

 

It's more whether or not the toning is attractive or if there is environmental damage. Dark stable toning is not a problem unless you try and dip it or if it is unattractive. Black, dark grey, and gunmetal colors seem to be neutral or positive (especially with circulated cameo) on silver types from this period, while dark brown tends to be neutral or negative in comparison. For copper, a nice solid chocolate brown is good to see, and helps protect the coin.

 

Appreciate the response. Let's say with Silver...my understanding was once it becomes completely black that the next step in the process is damage to the coin, is that not the case and reality is it's just permanently black at that point? If so that doesn't worry me at all and like that look like the one you posted, my main concern was buying a coin with black toning and 20 years from now the coin is damaged.

 

Silver toning is simply a chemical combination between silver and sulfur, forming silver sulfide on the surface of the coin. Past a certain toning thickness (and this is measured in molecules), there is no longer any "fresh" silver for the sulfur to reach and react with, and the reaction stops. Same for copper - that's why the Statue of Liberty (and copper roofs across Europe which are centuries old) have not rotted away.

 

It's interesting how the "pull-away" toning below the date has turned almost black. Usually, it is lighter than the other toning.

Chris

 

I feel likes its the eye of the beholder, I like some dark toning and some I don't.

My favourite dark toned in my collection(darker in person)

 

I'm not 100% sure that's true. I've seen a couple of older silver coins (Seated, Barber) that appear to have powdery black toning. I haven't tried wiping it away, but it looks like a situation where the toning layer is porous, and does allow further attack on the silver underneath. It may just be a matter of harsher environmental conditions...?

I'll see if I can find and photograph an example, but don't hold your breath. Busy times around the household...

 

Interesting; I know you're cognizant on the topic and would like to hear more if you find it. Wonder if the speed of the reaction (i.e., the concentration of available sulfur) has a bearing?

 

You can put a toned silver coin - even one which is near-black, in many cases - into an electrolysis process and remove the toning. As if it never happened. The original coin will return. No silver will be gone, or physically altered. Is that "permanent damage?"

This isn't some black magic; it's chemistry. It's a reaction between silver and sulfur to form silver sulfide, and it can be reduced.

 

IBetASilverDollar, posted: "Let's say with Silver...my understanding was once it becomes completely black that the next step in the process is damage to the coin, is that not the case and reality is it's just permanently black at that point? If so that doesn't worry me at all and like that look like the one you posted, my main concern was buying a coin with black toning and 20 years from now the coin is damaged."

Aside from the opinions here, I'll suggest you look on the internet for more info. IMO, GDJMSP has summed it up well. I'll add some things I think we all know. Toning is oxidation. Since it changes the surface of the metal, one prominent numismatist/chemist calls toning damage. In many cases it can protect a surface from further oxidation. When it is attractive it is called toning, when ugly tarnish. Toning is a cumulative process and the colors often change as it progresses. In most cases, the darker the toning, the more corroded the underlying surface will be. Black is end-stage.

jeffB, posted: "I've seen a couple of older silver coins (Seated, Barber) that appear to have powdery black toning. I haven't tried wiping it away, but it looks like a situation where the toning layer is porous, and does allow further attack on the silver underneath."

The black powder is a corrosion product. It is like soot on a surface. It will wipe off but that may leave a streak and often exposes a shiny black surface.

GDJMSP, posted: "But I think I must mention that terminal toning is in itself a somewhat subjective term. We can call it what it is because of what we see - when the toning is black it is referred to as terminal. But we don't really know, can't ever really know if it is truly terminal unless and until we remove it."

I've been playing around with terminally, black toned coins for years. Once the surface is black, the coin is corroded.

 

SuperDave, posted: "You can put a toned silver coin - even one which is near-black, in many cases - into an electrolysis process and remove the toning. As if it never happened. The original coin will return. No silver will be gone, or physically altered. Is that "permanent damage?" This isn't some black magic; it's chemistry. It's a reaction between silver and sulfur to form silver sulfide, and it can be reduced."

MY EDITED RESPONSE: Unfortunately, this poster (he has me blocked as I refute many of his posts) is seriously uninformed on this subject. I seriously doubt he has ever personally used electrolysis to restore coins!

I have . At this time, the surfaces CANNOT EVER be restored to their original state using electrolysis! As the poster said, It's chemistry.

 

GDJMSP, posted: "I won't claim that it can be done with electrolysis but it can absolutely sometimes be done by dipping a coin."

Allow me to use a "slick" political tactic..." It all depends on what "BLACK" is.

GDJMSP continued: "And I never claimed that black toning is always going to result in permanent damage,..." Of course you didn't, Insider did. "...quite the contrary in fact. As I said we can never know if irreparable damage has been done until the black toning is removed, and sometimes there is damage and sometimes there isn't."

"...I myself have dipped several black coins to reveal gorgeous luster underneath. And similar experiences are often related by many others within the hobby."

I cannot argue with experience, you and those others are either very lucky, the oxidation was not actually "terminal," or you did not look at the finished product as closely as I do. As I posted above: It all depends on what "BLACK" is.

 

@Insider what do you think of the coin I posted in the OP?

 

This simply isn't so. Or, at least, it isn't simply so.

Some metals form a coating that protects against further attack. This is called passivation.

Aluminum passivates in air, and that's what makes aluminum foil practical to use. If it didn't form a protective layer of aluminum oxide, aluminum would be attacked by even pure water, liberating hydrogen and turning into a pile of aluminum oxide.

Nickel isn't as reactive as aluminum, but it does something similar. That's why it can be used in contact with some highly reactive chemicals, up to and including fluorine gas.

I'm on board with "toning is a euphemism for corrosion", but saying "it's the same for all metals" is just wrong.

 

Not really, unfortunately.

When the coin tones, sulfur grabs onto those surface silver atoms, disrupting some of their bonds with their neighbors. When you reduce that silver sulfide, those silver atoms don't go back to their original positions -- in fact, they may not go back onto the coin at all.

You may not be able to see the surface changes at first, but they're there, and if the toning was deep enough or you dip/zap too long, you will see changes. The first hint is a drop in luster, because the microscopic ridges and furrows that cause it aren't that many atoms high; removing enough layers of silver atoms changes the topography enough to produce a visible effect.

 

JeffB beat me to it. Yes it is possible to reduce the toning and return the silver back to a metallic state, but the metal atoms WON'T be in the same place they were originally. If the toning was deep enough to have disrupted the luster, after reduction the luster will still be gone.