Artificially Toned Vs. Naturally Toned Vs. Intentionally Toned

Because pristine silver coins can be artificially tone to be very attractive, I do not ascribe any extra value to those coins.

Because it can sometimes be very difficult to tell the difference between artificially and naturally toned coins, I do not ascribe any extra value to those, either.

What you may find however, if you are very lucky, are 100 year old blast white silver coins in MS++ condition, just as if they had just left the minting press.
Such coins would be very rare, and thus should attract a higher value, well above their toned equivalents.

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To proceed to artificially tone freshly minted ASE's, and on sell them to those who like rainbow toned coins perhaps OK, but those buyers must preserve them in airtights, or they will be disappointed in future years.

While I realise this is a 7 year old thread, I will address the question in the title and OP, for the modern and future readers of this thread.

The problem with the whole "artificial toning" vs "natural toning" debate, or "intentional toning" versus "accidental toning", for that matter, is that we're talking about chemistry. Toning is just a chemical reaction: silver plus sulfur = silver sulfide. And chemistry literally could not care less about the "intent" of the people standing around while the chemistry happens. Neither the coin nor the environment care about anybody's intent, either. If the initial conditions are identical, and the chemistry is identical, and the result is identical, there is no empirical, scientific way of telling them apart.

Consider two scenarios.

Scenario 1: someone accidentally drops a silver coin into a bucket of motor oil. That sort of thing happens by accident all the time. The coin sits in the bucket for a month, and has all kinds of iridescent toning all over it once it's removed from the bucket and has the oil washed off.

Scenario 2: someone deliberately drops an identical silver coin into the same bucket of motor oil. It's certainly not hard to find buckets of oil, or silver coins, so this is also entirely plausible. The coin sits in the bucket for a month, and has all kinds of iridescent toning all over it once it's removed from the bucket and has the oil washed off.

Identical starting conditions, identical reaction time, identical reaction conditions; the only difference is in the intent of the person dropping the coin. So, what do we call the condition of the coins resulting from these two scenarios?

Are they both "accelerated toning"? Logically, yes, in that the toning happened much faster than "natural toning" from "normal environments" can normally appear, due to the coins being stored under sulfurous oil, which is not a normal or natural environment for coins to be stored in.

Are they both "artificial toning"? Logically, no, because Scenario 1 happened by accident, it ought to be classifiable as "natural environmental toning".

Can anybody tell the difference between the coin from scenario 1, and the coin from scenario 2? No. A difference that makes no difference, is no difference. There should, therefore, be no difference in market value between these two coins. The only basis for enhanced value for the scenario 1 coin would be "just trust me, it was an accident".

This is why the only pragmatic distinction the TPGs can make in regards to toning is "market acceptable" versus "market-unacceptable", where "market-unacceptable" is the kinds of toning that typically appear when accelerated toning methods are employed, or where scientific tools can clearly prove some "non-natural" chemistry has happened (such as silver chloride formation from a coin getting dipped in clorox bleach). So, are the coins from these scenarios "market acceptable" or not? That would depend on their appearance, which would in turn depend on the sulfur levels in the oil, the average temperature of the bucket over the month, and the "brightness" of the original silver coin. But the two coins would almost certainly be given identical verdicts by the TPG, despite the fact that one of them was "natural".