I've seen toning like this flagged as artificial in the past. What do knowledgeable experts here think?
If that’s what the coin actually looks like, I don’t think it’s original.
But I suspect that’s a big “if”.
Mark Feld* of Heritage Auctions*Unless otherwise noted, my posts here represent my personal opinions.
Iodine was used at one time to give gold coins a deep yellow-gold color. I think this type of AT has fallen out of favor among the coin doctors.
Worry is the interest you pay on a debt you may not owe.
I wouldn’t call that toning. Looks more like a putty job or something weird to me.
Some observations from an old time dealer on the doctoring process, I thought other chemicals like arsenic and mercury may be used by the coin doctors:
"Having served as technical consultant to the PNG Coin Doctoring Definition committee at the behest of John Albanese, let me address these points.
1) "orange peel" is not a toning characteristic. Rather it is a stippled surface quality resulting from mint-caused "die suction" during the striking process (second strike) and is not considered an impairment. It only occurs on Liberty Head proofs. I have seen it most often on $3's and $5's. Neither Michael Jordan nor LeBron James but @FredWeinberg is the GOAT on such topics.
2) Mercury will destroy silver by turning it dull gray. I have never heard of it used to tone gold,
3) Arsenic removes, not creates toning.
"While iodine works, virtually nothing else I am aware of chemically combines with the copper in gold without heat or electricity being applied. I can speculate on what might have "happened" to the coin in question, but based no my experience no natural process was involved."
Knowledgeable amateur here, but to me it looks like a weird camera angle and lighting highlighting the differences between the original untouched protected surfaces around the letters and the wear/rub from circulation on a mid AU coin.
I'm not so sure iodine reacted with the gold so much as it simply stained the surface. As for this coin, I'm finding it difficult to evaluate the photo. I don't see any toning, really, but as @clarkbar04 says, the relatively protected areas between the devices look a bit unusual. It could be an artifact of the lighting.