Any idea's

[Rich T]

Hi all, does anyone have any ideas on removing corrosion from copper.

 

This is a Yamagane piece, I think maybe Momoyama period, and it has about 3 small patches like this and some more thinly spread over the guard. I am wondering if there is an easy way to remove it ?.

 

Cheers

 

Richard

 

[John A Stuart]

Hi Rich, Copper so soft and easily damaged, as if it had to be said. Once you see the green it usually is trouble. But if very light might rub off by your fingers. Even then you can remove some of the desirable patina. Here's a link to an online PDF you might find helpful. John http://www.scielo.br/pdf/jbchs/v18n1/05.pdf

[Pete Klein]

I'm going to be a bit of a purist here but why remove it in the first place? Part of the beauty of the old yamagane pieces are the variations in patina brought on by age. I'd just leave it alone.

[Bungo]

lightly dip a Q-tip with chogi oil or mazolla or any cooking oil and rub rub rub gently........................chant any slogan while doing it can help pass the time.

 

milt the ronin

[Rich T]

I will probably leave it alone, I just wondered if there was an easy way to dissolve it.

 

Cheers

 

Richard

[Pete Klein]

In working with shakudo pure amonia (without soap) can be used to dilute copper sulfate which is used to help with the colouring. As this is probably a copper oxide or sulfate crystal it might work here also. Having said that I would suggest being very careful as it might colour the patina or remove it so use only the slightest ammount on Q-tip and be immediate to water to wash off if found necessary.

[Ford Hallam]

Hi Rich,

 

the green corrosion product on your tsuba is actually mainly composed of Copper(II) Acetate, or more commonly, verdigris. There will be other "pollutants" present but we need not concern ourselves with them.

 

Verdigris is soluble in water and alcohol, not the good stuff we drink though

If you want to reduce or minimise the deposit I'd suggest gently rubbing, or even stroking, it with a damp toothpick or something similar. This won't affect the more stable patina which you want to preserve, they're not water soluble. I wouldn't use oil as traces may remain and in fact contribute to further discolouration. Sorry Milt, although chanting may help.

 

The chemical reaction that has produced the verdigris is similar to rusting on ferrous metal but as long as the piece is kept as we generally keep our treasures, the ongoing corrosion being very minor is probably not anything to worry about. In more serious cases you may see bare, pink copper spots/specks or even nasty craters showing underneath the crust, this is the layer where the copper metal is being converted, by means of an electrochemical process, into Copper(II) Acetate. Arresting this sort of, more aggressive corrosion, is a specialist job, for a trained conservator.

 

Hope this helps a little,

 

regards to all, Ford

[Rich T]

that sounds like a good plan to me. I might give that a try. And thanks Pete for your suggestion as well.

 

Cheers

 

Richard

[Pete Klein]

Well then -- after linking to verdegris in Wikipedia I now know why the foliage in so many old European master's paintings are brown!

Thanks Ford.