Byzantine with strange surface

I have a Byzantine with rough folds or blisters on the surface. It measures about 31 mm in diameter. I can't make out all the details yet. One side is completely unrecognizable as yet. Additionally, the coin seems to have been silvered. I don't want to clean it further until I know what is going on with the surface. Can you see the silver coming through?

 

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It may be have been damaged by fire.

 

Thanks. That is a possibility.

 

My first thought is that it was acid cleaned. What remains includes remnants of corrosion products.

SC

 

I don't think there is any silver. Hard to tell if anything can be cleaned up on the coin. It looks like it was already harshly cleaned. But it definitely is a 40-nummi piece.

 

OK, what is a "40-nummi" piece?

 

Follis. M stands for 40 nummi, K for 20 nummi, X for 10 nummi, etc. The nummus was tariffed to the solidus.

 

Thanks. I didn't know that.

 

I have always associated this condition with long term immersion, like it was lost in a lake, or a bath, even fountain. I have detected a lot underwater, and the electrolysis that happens naturally is crazy sometimes. I have found things in the water that look like these types. I conserve dug coins, have done many thousands, these are fairly common and many times cannot be identified.....b

 

Thanks. Every bit of information helps.
Welcome to CT

 

I'm putting this Byzantine back up looking for a little help. I find it to be:
Justinian I with mint mark CON and Right Field to have X X III in vertical configuration.
That's as far as I can get.