Strange green material on the obverse...

Shocktrooper · 05-18-2008, 01:01 AM

Hi,

what`s that green material on the surface of my Prague - medal ? It has the consistency of modelling material. May it be that it`s a rest of a mould (cast copy) ?

Thank you very much,

Jens*

Kirchgoens · 05-18-2008, 10:53 PM

I've seen a similar compound on a "Valiant Labor in the GPW" medal that I know was not faked. Often this green color can come from tarnish with brass compounds, so I wouldn't be surprised if this was either some sort of common Soviet-era polishing compound, or just residue of polishing mixed with dirt/grime/oil.

***desantnik*** · 05-19-2008, 05:43 AM

It often exists on old bronze coins too, called verdigris.

Shocktrooper · 05-22-2008, 11:11 AM

E.g. : I know the copper oxide called "verdigris", but it`s very hard and difficult to remove off the surface. The material on my medal is soft like a paste; so I think it could be soviet - era polishing material as mentioned before.

Jens***

Nota Bene · 05-22-2008, 08:34 PM

Jens,

I guess it's impossible to tell from the picture one way or the other. It probably depends on the amount of copper in the alloy, but sometimes verdigris can be easily removed.

Alexei

Sergei · 05-22-2008, 09:24 PM

Nota Bene,
And once it's removed, is there a simple way to protect the medal from it coming back? I heard of vaseline and varnishes but never tried those.
Thanks,
Sergei

Kirchgoens · 05-23-2008, 11:20 PM

Another reason I think that there may be some sort of polishing compound involved is that that old VL-GPW medal also had the green gunk on the suspension and ribbon. It was very greasy. An odd but effective solution: I boiled it. It removed most of it as the gunk went liquid and formed a layer of oil in the pan. Once the pan cooled, the gunk settled along the edges, making it tough to get off the pan!

Nota Bene · 05-31-2008, 03:07 PM

Quote:

Originally Posted by Sergei

Nota Bene,
And once it's removed, is there a simple way to protect the medal from it coming back? I heard of vaseline and varnishes but never tried those.
Thanks,
Sergei

Sergei,

Anything, the protects it from the environment will do. There are also commercially available solutions for protecting coins.

Alexei

Shocktrooper · 06-09-2008, 10:38 AM

Hello again,

thanks a lot for your posts, impressions and ideas !

This way we can move forward.

Jens !

05-18-2008, 10:53 PM	#2
Kirchgoens Senior Member Join Date: Apr 2007 Location: US Mid Atlantic Age: 57 Posts: 351	Green gunk... I've seen a similar compound on a "Valiant Labor in the GPW" medal that I know was not faked. Often this green color can come from tarnish with brass compounds, so I wouldn't be surprised if this was either some sort of common Soviet-era polishing compound, or just residue of polishing mixed with dirt/grime/oil.

05-22-2008, 11:11 AM	#4
Shocktrooper Senior Member Join Date: Mar 2008 Location: Germany Age: 48 Posts: 105	Re: Strange green material on the obverse... E.g. : I know the copper oxide called "verdigris", but it`s very hard and difficult to remove off the surface. The material on my medal is soft like a paste; so I think it could be soviet - era polishing material as mentioned before. Jens***

05-22-2008, 08:34 PM	#5
Nota Bene Senior Member Join Date: May 2002 Location: New York USA Posts: 2,296	Re: Strange green material on the obverse... Jens, I guess it's impossible to tell from the picture one way or the other. It probably depends on the amount of copper in the alloy, but sometimes verdigris can be easily removed. Alexei

05-22-2008, 09:24 PM	#6
Sergei Senior Member Join Date: Jun 2006 Location: London, UK Posts: 199	Re: Strange green material on the obverse... Nota Bene, And once it's removed, is there a simple way to protect the medal from it coming back? I heard of vaseline and varnishes but never tried those. Thanks, Sergei

05-23-2008, 11:20 PM	#7
Kirchgoens Senior Member Join Date: Apr 2007 Location: US Mid Atlantic Age: 57 Posts: 351	Re: Strange green material on the obverse... Another reason I think that there may be some sort of polishing compound involved is that that old VL-GPW medal also had the green gunk on the suspension and ribbon. It was very greasy. An odd but effective solution: I boiled it. It removed most of it as the gunk went liquid and formed a layer of oil in the pan. Once the pan cooled, the gunk settled along the edges, making it tough to get off the pan!

05-19-2008, 05:43 AM	#3
*desantnik* Forum Moderator Join Date: Oct 2004 Location: Eurasia Posts: 2,338	It often exists on old bronze coins too, called verdigris.

06-09-2008, 10:38 AM	#9
Shocktrooper Senior Member Join Date: Mar 2008 Location: Germany Age: 48 Posts: 105	Re: Strange green material on the obverse... Hello again, thanks a lot for your posts, impressions and ideas ! This way we can move forward. Jens !

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