Is This Toning Natural? (1890 Morgan Dollar)

If by "natural", you mean that the toning arose without the direct intervention of a human being, whether accidental or deliberate (ie, seeking to elicit a particular change on the surface of the coin), such that a competent TPG would give it a straight grade, I'd have to give this answer: probably not. The colors seem a bit heavy on the sort of greens & blacks one sees a few years after low-ph sulfonate detergent remnants & partially dissolved oils have a chance to adhere and solidify on silver, like the tarnish on silverware that had been hastily cleaned then tucked away.

(There's also a bare hint of iron rust with that cupric green. Maybe it's nothing, but you should confirm that the coin is actually genuine and made of silver, and doesn't contain the iron found in Chinese fakes.)

Assuming the coin is genuine, I'm pretty sure it would elicit a "cleaned" grade, once it was looked at it under a microscope and swabbed for residue. (Of course, I'm just looking at a photo. I'm also really f&*!ing old, and my IQ is apparently dropping by one or two points a month.)

If by "natural" you mean that the surface of the coin changed spontaneously, with no anomalous environmental input, then no, it *definitely* isn't natural. Something accrued onto the surface of this coin that is gradually reacting with oxygen, silver, and the oils & proteins found in fingerprints. That "something" could be an alkylbenzene from a detergent, or a variety of weak acids that slowly leach from paper & cardboard, including those used to make things like envelopes, boxes and even coin albums.

Colorful toning on lightly-circulated coins often develops after chemical cleaning (dipping). It's not usually a positive attribute. Attractive toning on original uncirculated silver coins, however, can add significantly to their value.

I agree this coin looks a little suspicious. The D and A in DOLLAR seem malformed and the overall color is typical of non-silver counterfeits. I'd first check weight (should be close to 26.7 grams) and see it it's attracted to a magnet. Even if it checks out as genuine it would have a common-date value, perhaps $35 or so.

Do we have the weight yet?