How fast will verdigris spread on slabbed silver coins

[youliveyoulean]

Hi all,

I've often wondered with a few of my slabbed silver coins which have the tiniest pin prick of verdigris, will this likely spread at any point and to what extent?

Love to hear other thoughts on this...

[IanB]

I hope that I am not wrong in saying that verdigris cannot form on silver. 

I believe that verdigris is a chemical reaction between copper and the environment, I an not a chemist so please don't ask me to try and explain it?

Can you post a picture of your coin?

 

Edited November 27, 2016 by IanB

[youliveyoulean]

Thanks for replying Ian.

I'm pretty sure you can get verdigris on silver coins (perhaps there's just a technicality with the name which could be a different type of chemical reaction to that of copper?) - the grading companies certainly reject silver coins for verdigris or some kind of corrosion of green appearance.

 

[IanB]

You maybe right, silver is alloyed with copper in various ratios. So I suppose the chemical reaction could still take place.

I don't have much experience with silver coins but I am guessing someone on here will have the answer.

[PWA 1967]

In some instances the verd has been removed and then sent for slabbing ,this means that at the time of grading wasnt there but always the chance of it coming back over a short period of time .

The coin is not going to get any better.

If your not happy break it out and remove it ,alternatively just have a quick look every few months 

[IanB]

As far as I am aware for verdigris to spread the conditions that have caused it need to be present. It is not alive, it's a chemical reaction.

Remove the conditions and it will not spread.

 

[PWA 1967]

24 minutes ago, IanB said:

As far as I am aware for verdigris to spread the conditions that have caused it need to be present. It is not alive, it's a chemical reaction.

Remove the conditions and it will not spread.

 

So does that mean it wont come back Ian ?.

[IanB]

13 hours ago, PWA 1967 said:

So does that mean it wont come back Ian ?.

I am not a chemist so I cannot accurately say why verdigris appears but I believe it is a chemical reaction between the metal and the environment that it is in. Unfortunately the coins we like to collect are made of the metal that is the most likely to have this reaction, add to that moisture, bad storage and whatever else they react with and verdigris is one of the side effect.

like most chemical reaction if you can remove a part of that reaction it will stop. 

If a coin has some verdigris on it and it is continuing to grow then the conditions for it to do so must still be present.

I have read that a small amount of baking soda will neutralise the reaction. If that is the case, and I have no way to prove it other than what I have read, then once it is stopped then as long as the other factors are controlled why should it grow again?

 

Edited December 3, 2016 by IanB

[PWA 1967]

Thanks Ian.

What i meant really but did not explain is if i just remove some and nothing underneath ,but without using any chemical etc.

 

[IanB]

It's just my opinion but I believe that if a piece of verdigris is flicked off and there is nothing left on the coin and the coin is not exposed to an environment that encourage the reaction needed for verdigris to occur then it will not come back.

The problem we have is controlling the factors that cause it. 

If we think about the above example of a coin with a spot of verdigris that is loose on the surface, at some point the conditions were perfect for it to start appearing maybe it was a small piece of sweat from a finger or moisture from a breath. Whatever it was it landed on the coin and started the reaction with the metal, maybe it was stored in a room with fluctuations in temperature and a spot formed. 

Then someone comes along and flicks it off, as long as it loose and comes away clean and completely then that verdigris is gone. 

If verdigris reappears on the coin then the conditions for it to be there have not been controlled e.g. Poor handling, storage, temperature etc. 

Edited December 3, 2016 by IanB

[Nonmortuus]

Rather than start a new thread I thought I would post here. I have a German Mark that is slabbed by PCGS that has the slightest pin prick of Verd on the reverse. It is not a high value coin being a 1914 D but would you break it out and treat it or leave it in the slab and see how it develops?

[PWA 1967]

I would just leave it Paul it must be small to only be able to see under a microscope and not worth bothering about if a cheap coin anyway.

[Nonmortuus]

Cheers Pete, that was zoomed in with my phone. The coin is very nice that tiny spot aside.

[Sword]

Sometimes it is quite difficult to tell (for me anyway) if a green spot is actually verd or something else (surface junk, "dirt" etc etc). 

The coin is 90% silver with presumably 10% copper and so I guess verd is possible but not that likely. 

I agree with Pete that it is best to leave it in the slab. No point wasting the slabbing fee. And if you want to upgrade in the future and sell it, there are plenty of buyers just interested in PGCS grade numbers anyway.

 

 

[Rob]

The area immediately above has a clearly rounded line which suggests it might possibly be badly mixed metal with a little inclusion spot

[argentumandcoins]

Technically verdigris should not spread at all in a slab as they are supposed to be hermetically sealed.

[Sword]

3 minutes ago, argentumandcoins said:

Technically verdigris should not spread at all in a slab as they are supposed to be hermetically sealed.

Hermetically sealed just mean the slab is airtight. But I don't think the coin was sealed in vacuum. So I think in theory, the air (+ contaminants in the air) inside the slab can react with the copper content of the coin and produce verd. VS' 1935 specimen crown in a CGS slab is a good example to look at.

[1949threepence]

14 hours ago, argentumandcoins said:

Technically verdigris should not spread at all in a slab as they are supposed to be hermetically sealed.

Hmm, that's what I thought. Moreover, that the same principle applied to carbon spots. Although in this post from December 2011, I was told to expect the carbon spots in a slabbed MS65 1888 penny, to grow over the years. For reference, 5½ years later, there's no detectable change.   

ETA: Some very interesting and helpful posts about verd here, although not in relation to slabbed silver.  

 

Edited July 29, 2017 by 1949threepence