Silver obol from Massalia - 3 years later, some spectacular cabinet toning

For some reason, this little silver obol from Massalia has really gone to town with the toning in the three years it's sat in my coin cabinet. It was essentially stripped when I bought it, and now it's quite a colorful little piece. I like it.

There are a few other silver coins that have developed hints of iridescent toning after sitting in my cabinet for a couple years, but nothing like this coin! Let me know what you think.

Before and after:

GAUL, MASSALIA
AR Obol (11.04mm, 0.73g, 2h)
Struck circa 300 BC
Obverse: Youthful male bust left
Reverse: Four-spoked wheel, MA in two quadrants
References: De La Tour 689
Good flan quality. Deep iridescent toning. Massalia was a Greek colony founded around 600 BC on the southern coast of modern-day France. Notable natives of Massalia include the great explorer Pytheas the Greek (fl. c. 320 BC), who travelled up the British Isles and as far north as Iceland, and later described his travels in a book entitled On the Ocean.​

 

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Charge by the year.

 

I'd wonder what chemicals are in that cabinet (or the house) doing this and what they might do over the next few years. It might not be so pretty then.

 

Mighty fine look, I have a few cabinets, mine are reacting much slower than the obol above. It's a perty coin.

 

The wood cabinet is made of walnut, finished with boiled linseed oil. So it'll be slightly more tone-prone than, say, unfinished mahogany.

I'm guessing the coin will continue to darken over the years, unless I do something to protect it from further toning. But I also believe that the rate of toning slows over time, so it might take longer than expected to reach that state.

 

It's weird, like I said, most of my other coins haven't shown nearly this level of change. I wonder if it has to do with how chemically clean they are, and maybe the purity of the silver? This obol might have been stripped squeaky-clean and that's why it toned so quickly, while the denarii in my collection might have some sort of protective layer still intact (be that oil from handling, wax, or just previous layers of toning.)