An Atrocious Tasmanian Token

OK, up till now, nothing much has actually afected the verdigris - only the oxidation, which I was trying to preserve. Next step: try a few different chemicals, which I'd heard might be helpful.

First off was ethanol, in the form of methylated spirits. If the problem is primarily copper acetate-based, a nice soak in alcohol ought to do the trick. I tried it for 15 minutes and... nothing. Whatver this coin's problem is, acetate isn't it.

Next up was ammonia. And not the nice, safe, mild "ammonia" you can get from off the supermarket shelf, either - this is lab-grade stuff, 25% pure (you can't readily buy it any purer; ammonia is a gas at room temperatures) and no other fancy ingredients.

Here are the results. I must say that this time, I'm impressed that something like what I was hoping would happen, actually happened :


At least the verdigris isn't ignoring me anymore! Check it out - it turned blue and dissolved away!

This is the result after a half-hour-long soak, with a solution replacement halfway through - far longer than your typical verdigrized coin ought to need, but still not quite long enough to wash away all the blue stuff. Still, it seems to be completely gone from the obverse (emu and kangaroo side) and it shouldn't take much effort to remove the remaining stubborn spots.

There are, of course, serious craters where the verdigris disappeared from - but I expected that. I don't think there is any way of removing verdigris without leaving pitting behind.

Again, a warning - the ammonia I used was quite strong. I was doing this test in an industrial fume cupboard; I took one inadvertent whiff of the concoction, and my nose stung for hours afterwards... Anyway, some more "trial and error" needs to be done, to see if the verdigris comes off a "raw" coin (i.e. one that hasn't been soaked in olive oil, citric acid, etc.) without damaging the toning, and whether diluted, commercial-grade ammonia solutions can do just as good a job.

I gave it another hit with some more ammonia this morning - all the blue is gone, now. It looks exactly the same, otherwise, so I'll save everyone's bandwidth and skip a final picture.

Conclusions
Is the coin more valuable, now I've cleaned it? No. (Not unless I sell it on ebay with a very fuzzy picture! It may not look "green" anymore, but it sure does look "cleaned".

Has the appearance been improved by the cleaning? Qualified yes. I could probably have done a bit more homework and erased the verdigris while leaving the undamaged surface more intact. And the orange-brown pits left behind are ugly and unattractive, without a doubt. But the verdigris was unattractive, too, and not cleaning it (i.e. leaving the verdigris there) would have been detrimental in the long run - the next generation would likely have inherited a crumbly green lump that might have been a coin once.

Is the coin something I'm proud to keep in my collection? Sure, why not - I don't have any other tokens from Westbury.

Is this the end of the story, for this token? For now. I'm going to have to keep and eye on it for a few years yet, to make sure the evil green is really gone, and not just in remission.

Congratulations Professor Sap!

I used your ammonia method, with lots of success. You should patent it! I had to use the mild ammonia that is available in supermarkets, as it was all I had on hand. I ended up soaking the coins for twenty hours in the ammonia and found that it worked wonderfully.

The pitting on some of the pennies looks pretty awful, I must admit, but then they didn't look too good covered with green either. I nearly had a heart attack when I saw the ammonia after twenty hours soaking, it was the most incredible, bright blue that I have ever seen.

However, I think that we have defeated the dreaded verdigris! You may find, Sap, that I now contact you every time I have a coin problem, so you may regret being this helpful!

Thank you for an interesting and informative thread on your experimentation. I just have to come to the coin forum more often!

Hi Sap,

I only did it to the absolutely worst coins imaginable, so that no matter what happened it wouldn't matter. Also, the 20 hours shocked me too. I kept checking them constantly, but nothing happened. Eventually I gave up and went off to bed for the night, deciding that if nothing happened overnight, then nothing was ever going to happen. I'll keep an eye on them for a while before I try my next batch.

Thanks for your help.

I have this brazilian coin, from the 20's, and it has some verdegris on it. It is not particularly valuble, and I suspect it is made of copper nickel... any ideas on how to get that green stuff off?

andrew

Wow Sap this whole thread is fantastic and very educational

Sap, how did this end up ?
Peter in Darwin