Heavy Metal Oxidation

harasha

Unfortunately, not some rock group.
A bronze metal I had bought some time ago on ebay turns out to be subject to heavy oxidation. Is there some way to treat this item to cure this green monstrosity?

Sylvestius

<< <i>Unfortunately, not some rock group.
A bronze metal I had bought some time ago on ebay turns out to be subject to heavy oxidation. Is there some way to treat this item to cure this green monstrosity? >>




Green? That's not oxidisation... that sounds alot like a certain hydrated copper carbonate (although sometimes apparently it can be Copper Acetate as well). Which leads me to another question...


It wasn't a lustrous bronze medal when you bought it was it?

harasha

It wasn't a lustrous bronze medal when you bought it was it?

Oh no. In the ebay photo it looked like any other Dupre medal, with the usual normal toning.
I purchased it back on July 5, 2004.
I doubt if the photo is still around, but I will look.

Sylvestius

<< <i>It wasn't a lustrous bronze medal when you bought it was it?

Oh no. In the ebay photo it looked like any other Dupre medal, with the usual normal toning.
I purchased it back on July 5, 2004.
I doubt if the photo is still around, but I will look. >>




I was only asking because Copper Acetate would only form if exposed to acetic acid (vinegar).

Which means it's likely to be a copper carbonate resulting from carbon dioxide in the atmosphere mixing with the water vapour and reacting with the copper, forming verdigris. We discussed what would be best for removing verdigris a few weeks back on another forum and the generally conclusion was varying. I'm sure someone said the usual dip in acetone wouldn't work, whilst someone else said it might.

Either way if it is verdigris which is what i think of when someone says the coin is green then it really does have to come off, leaving it will only make it worse. I wish i could advise you further upon this one but you're best waiting until someone comes along with an idea or two.

The advice i generally give (which goes with silver coins and is only applicable to localised Verdigris) is to scratch it off with a fingernail. Sounds a bit brutal considering you might be able to dip it, but dipping would destroy the tone. Catch 22.

VF - Slight scratch
VF - Cleaned

Which sounds better? Heavier localised damage or lighter but overall damage?

Since you indicate it's got an whole over green look and is bronze my method is not advised. Generally beause it wouldn't work for overall, but it's never advised with bronze because of the way they tone having a lustrous scratch is never too good. Less noticable with silver.

harasha

Thanks. Anything would make it look better, I think. The seller, by the way, is still around, and has a 99.9 rating. The one negative is clearly a fluke. In fact, while I was looking at his feedback, I noticed some well known ids, including, ta-da, Askari. Hope he is doing well.

Aethelred

<< <i>Unfortunately, not some rock group. >>



What are you talking about, they were one of the best 80s bands!

MrSpud

You could try soaking it for a while in either mineral oil or olive oil. I have also heard of people using things like rose thorns to scrape off some types of verdigris (for coins that aren't mint state or proofs). I believe that they oil the coin heavily before using the thorn. EDTA, a chelating agent can also be tried. I did an experiment once with a copper coin with green corrosion where I treated it with EDTA and posted before and after pics. Some people liked the results, others thought it changed the color too much for their liking. Here is a link to the post edta . I have also heard of other people trying various forms of electrolysis, putting the coin in a potato and even people using goo gone on copper coins with corrosion with varying degrees of results. I imaging bronze behaves somewhat similar to copper.

theboz11

Soak it in xylene ( Glass bowl on cotton, well ventilated) for a week and use a thorn and it will come right off, and not change the color. Rose or Bugenvillia(sp) work well. If you have a binocular microscope you can easily see the removal under 20 power.

If it is still present use MS-70 on a Q-Tip sightly soaked and it will finish the job. Be carful as MS-70 used to heavily may remove tone, but will not bother or brighten like a dip..