Restoration of pewter (black incrustations)

Hello,

does anyone know non-harmful methods of conservation to remove black incrustations on pewter medals/coins?

I have this Russian medal which seems to have quite a decent grade and seems to be also quite scarce.
It is however almost entirely covered by a thick-looking crust.
As I wrote above, anyone have an idea how to get rid of it without damaging the medal?
I tried acetone but seems not to be having any effect.



Regards,

Paul

That looks like a medal that I got a while ago!

https://en.numista.com/forum/topic38951.html

I already identified it, its the same as this one here https://www.acsearch.info/search.html?id=812678

Hi Paul,
try to have a look at this site: http://www.howtocleanstuff.net/how-to-clean-pewter/
Since I don't have any pewter coins or medals, I have never needed to even think about it. As usual make sure your treatment will leave no "scratches" on the surface of the object....
Ole

But, it looks so good in black!

At the moment I could not see a way that I find acceptable to get rid of the black incrustations, so I will let it like this.