Bactrian Gunk

[Frank M]

I am cleaning a sliver coin that I bought on Ebay. The listing photos are below.

There is a pretty silver coin under the black gunk pictured.

I have cleaned a decent number of coins but this particular blackish stuff is new to me. It has a consistency somewhere between wax and lead.

The encrustation hasn't responded to electrolysis, or the usual mild acids and bases like vinegar, ammonia, ethanol, acetone.

The rest of the coin sure is clean though!


Working under a microscope, I can slowly pick it away from the clear markings, but it is very laborious and I have over cleaned/abraded the coin (very slightly).

The gunk's resistance to solvents and such makes be wonder if it isn't lead? It hasn't leached out of the coin as there is a clear tactile and visual difference when you get to the silver. The coin is separate from any corrosion layer.

On occasion, the gunk will peel in large flakes rather than smaller, waxy shavings.

The listing photo of the reverse shows the gunk most clearly

Thoughts?

Thanks!

[SC]

A form of horn silver?

Shawn

[Frank M]

Here is where I have gotten it.

My coin lighting isn't totally dialed in yet, but you get the idea.

[Frank M]

I started working on the despit after soaking it briefly in blowing water to try to loosen up whatever is stuck on there. These close up don't show nearly as much as you see under a binocular microscope but you can see a trench I have made in the gunk with a probe. There is a little flake of it at the top of the coin.