Cleaning Help Ideas For This Decentius?

You might want to try soaking it in olive oil, I think trying anything else will remove whatever patina is left on the coin.

I will be watching this with interest...

I have a coin with a very hard mineral deposit on it and if there is a solution to your coin maybe I will try it on mine.





Looks like the only thing that would shift it is a power tool...and I am not that brave.

How hard is the green? Does a toothpick touch it?

David try soaking it in some diluted warm white vinegar.

Paul,
I have a similar coin with a similar verdigris deposit. Needle and microscope is my approach. It is slow going, but with care it effectively removes the layer without too much impact on the patina. But you may expect that the verdigris is bonded to the patina, and so your movements of the needle must be to split the layers. I can only work on mine for short intervals, and only occasionally take it out. But once removed it does not return.

I'll try to post a pic of my progress if I can find one.

David,

You might want to check that "deposit" before you remove it. I have a a few silver coins like that, and the dark stuff turned out to be what is sometimes called "horn silver" That is a chemical alteration of the silver of the coin, and if that is what you've got, it will leave a scar (pit) if removed.

Paul,
I could not find my example for Decentius or Magnentius or whoever it was, but here is a piece I have done some work on from Maximinus II with the same problem. I'm sorry I don't have a "before" shot, but before I started the reverse was uniformly covered with the green you see still on it.






In the close-ups you can see that despite some occasional "brassing" the patina is largely intact. If treated chemically this would all have been stripped. One point I did not mention before is illustrated by the right close-up, namely that sometimes the verdigris is a layer on top of some other accretion. These can complicate the removal process, so you have to be alert for the possibility they are there.

[EDIT: I forgot to mention that I have not touched this coin for ten years now, so I am reasonably sure that the surfaces are fairly stable as you see them. Once deposited the verdigris does not hurt the underlying metal of the coin, and the only reason to remove it is for reasons of appearance. Here conservation and presentation are in conflict.]


David,
I thought you might like to see the ravages of horn silver (a mineral form of silver chloride) on a coin that I am sure is of interest to you. (Sorry for the quick and dirty scan; I wanted to get this up quickly.)



This coin was afflicted and treated before it came to me over 30 years ago. I don't know what was done to treat it, but I doubt if I could have done any better. The loss is irretrievable, but in some sense necessary so that the mineral conversion can be stopped. It is stable now, but hardly a showpiece. Thank goodness it still has a presentable side.