PVC infested coin or just harmless toning on 1905 Straits 50¢

This coin was stored in 2X2 cardboard Mylar for 2 years. Recently I notice the stain is more obvious than it was 2 years ago.



I had soaked the coin with pure Acetone, rinse with distilled water ensured air dried prior to archive into the 2x2.

Is it the harmful PVC or natural toning? I hope there is no sign of corrosion on the coin. When I remove the coin out from the 2X2 there is no gluey substance on the coin and the mylar did not stick to the coin. Those stain area does not feel particularly sticky too. Below attached is closed up image of the coin.



The reverse looks slightly cleaner



If that's PVC what remedy can I do? What is your opinion, harmless toning or the dreaded PVC?

Kindly advise
Thanks

You could try ultrasonic cleaning and see if the stain is removed other than that I'd leave it as it is.

"PVC damage" comes from the plasticizer used in PVC flips. If this coin was stored in a mylar 2x2, then it's just natural toning.

Green natural toning on silver coins? What can cause it ?

Maybe there is copper present in the silver. I've read that silver coins can turn green if they have been alloyed with copper. According to Numista your coin is 0.800 silver this might account for the green tinge showing through over time.
https://en.numista.com/catalogue/pieces15531.html