Hello everyone. I was hoping someone could shed some light on this challenge coin I found back in 2007 when I was at Guam, I think it may be diseased (verdigris). If it is, and I suspect it is, I want to clean it and stabilize it. I'm not concerned about the pitting and damage that has already happened. I would like to keep it from getting worse. I think when I found it - back when I didn't collect - the patches of white were green and smaller. The colors are fairly accurate, and it appears to be made out of bronze or maybe brass.
Brass and bronze are mostly copper. This is supposed to be the be-all, end-all of wonder fluids for copper. http://www.wizardcoinsupply.com/products/verdi-care.html
Verdigris is usually light powdery green. It wouldn't hurt to treat it, but I am unsure if its verdigris at all. Btw, pm @BadThad, he would have GREAT information about the product Rick linked, (he makes it).
The coin is definitely corroded but it sure doesn't look like verdigris to me. Looks more like the ordinary (white) corrosion you find on water pipes.
ANY copper corrosion can be correctly classified as verdigris since it really is a generic term. Many compounds form cupric salts, i.e. hydroxide, chloride, sulfate, acetate, etc. All types are considered verdigris.
Fair enough Thad, you're the chemist not me. I've just never seen any, on coins anyway, that wasn't green. On copper pipes, yeah it's quite common. The stuff works, there is no question of that. I've tested it myself and so have many others on this forum. But Thad's own data sheet says that on coins with heavy verdigris it may not remove all of it. In other words it's a question of severity, the more severe the verdigris, the less likely the product is to remove all of it. But it will always remove some, or even most of it. But users of the product must understand, even if it removes all of the verdigris from a coin, the product does absolutely nothing to repair or lessen the damage done to the coin by the verdigris prior to its removal. All it does is take away the powdery residue of the corrosion, leaving behind any pitting on the surface of the coin. And there IS going to be pitting for that is what corrosion does.
Thanks. I was curious because I've seen it advertised for copper but was unsure VerdiCare on brass or bronze. I have no idea what metal the "coin" is made of.
Maybe, it's hard to tell from just a couple pictures. Like any conservation project, the results vary depending on many different factors. The bad news for this token, the surfaces appear to have been permanently damaged by the corrosion. However, I am confident it would at least see some improvement and VC will halt the corrosive process.
I agree. From my own experience, I use the handy tools Thad provides to try to remove the worst of it, then apply VC to the coin. I let it sit for a while, maybe scrubbing a little more. Afterwards I let dry, (maybe soaking in acetone), and if it doesn't appear its all removed I do it again. I have been able to arrest all incidents of verdigris with his product, even severe cases, though severe cases usually require multiple treatments. Unfortunately I collect some bronze ancients from areas very prone to verdigris, so I buy my product from Thad in the largest bottle he makes. Regarding damage, yes you are right. There will be pits on the coin. Simply remember those pits were there BEFORE you removed the verdigris, and if you HADN'T removed it eventually the verdigris would have totally devoured the coin.
Yes, I've removed a lot of different surface residues on silver coins including PVC. However, I prefer acetone for PVC. I use it, then a little VC (to neutralize any residual acid), rinse with DI, rinse with fresh acetone and the coin is ready for storage.
