A mysterious transformation

Well here is an educated guess: since the blueish patina was in fact a rather thin layer of silver sulfide, artificially applied to the coin in higher concentrations than coins that tone naturally, the process of Ag + S >> Ag2S was probably still ongoing - and likely way faster than other coins that tone naturally. As @shanxi points out above, thin layers are blueish, and thicker layers become grey to black.

Now lets focus on the coin:

Although I obviously didn't see the coin in hand, the blue patina is most profound under the legend AEGYPTOS on the reverse (9-12 'o clock), and a bit on the bust - the other area's are greyish. So we have a blue thin layer on the bust and on the reverse, with thicker grey layers on other area's.

Now with progression of time, your coin turned grey more homogeneously - this below is your coin (I've edited your images a bit)

The layers that were gray or only slightly blue (the thicker layers) became thicker due to the process of artificial toning that was still ongoing, while the area's that were more iridescent blue are almost 'done'.

Now a short note on the redox reaction described above, and the effect on ancient coins. In my experience, silver sulfide (i.e. the patina that most collectors 'want' on a coin) starts in the more grainy, (microscopically) pitted area's. The redox reaction strips the silver sulfide, and exposes the underlying surface. Also, with the removal of silver sulfide, one does not only remove the sulfide, but also the silver (...).

I've magnified your 'before' and 'after'. Now this may well be overinterpretation, or due to differences in lighting, but this is the effect of the redox reaction that I meant above (and the reason I usually use other chemical methods):
Before:
After:

 

Log in or Sign up to hide this ad.

Thanks for the explanation. I don't see that much difference between the "before" and "after" photos with respect to immersion in the solution. I hope you're not planning to tell me that the 2-3 minutes that the coin spent in the solution ruined it!

 

LOL, I dunno, Donna. I kinda like the Blue Toning. Kinda goes well with the Picts that the Romans hid behind a wall from:







Roman Empire
Hadrian
AR Quinarius
1.3g, 14mm
Rome,
CE 119-122
cuirassed laureate
COS III Victory seated wreath palm
RIC 108a

 

Donna, Thanks for posting your experiment . I don't think I'd have the patience to wait 4.5 months for a result .

 

I was fascinated by that vendors coins. Bit of a letdown that this is artificial:

https://www.vcoins.com/en/stores/at...roduct/hadrian_ad_117138/1096805/Default.aspx

 

I would be highly suspicious of any sort of "interesting" toning in that seller's coins, blue or otherwise! Especially when the seller's description expressly refers to the toning. I actually bought another coin from them in the last few months, but it was one that showed no signs of toning. Another deterrent for me is that I think their coins are a bit overpriced in general.

 

I have seen that they offer lots of blue toned coins which I find suspicious. All have kind of same blueish colour. I was thinking they're doing it themselves chemically so they can charge much higher prices. At least what I've seen same graded coins without the toning goes for much lower prices. I myself will not buy anything from them.

 

An interesting discussion. Whenever this topic comes up I can't help myself and feel compelled to post this.

It is a sestertius of Antoninus Pius that I bought fer cheap on eBay. It had the most unusual blue toning! But when I got it in hand, I noticed it was sticky - somebody had painted it blue. It came of in seconds with, I think, a little hand sanitizer. I left some blue in the crevices as evidence of its colorful past. If it hadn't gotten sticky on me, I probably would have left it blue.