Pair 17 S Obverse Walkers with conservation issues. Don't cry.

[jsilver2th]

Hi- Here I have a pair of 17 S Obverse with some condition issues as you can see. I would be interested to see what comments anyone may have about the coins and what you may think are appropriate conservation steps. The main issue is obviously the "green" vertigas or whatever- Thanks in advance for your comments and I welcome all and any perspectives as I quest for knowledge. Thanks JS (Sorry the pics could be better- I am still working on that one.)

 

A 1917 S Obv Walking Liberty Half Dollar

A 1917 S rev

 

B 1917 S Obv Walking Liberty Half Dollar

B 1917 S Rev

 

[BadThad]

These are 10% copper. It's definately verdigris and could have been initiated by PVC (formation of cupric chloride). The first step in this case would be an acetone soak in case there's any plasticizer residue. Soak for a few hours and at the end of the soak, while the coin is still under fluid, gently work the verdigris with a toothpick (if it's still there). If the green is gone, congratulations, you had PVC. If it persists, you'll have to use either NCS or alternative methods to address it. Otherwise, you can just dehydrate the verdigris with acetone and immediate put it into an airtite holder for storage.

 

Dehydrating the verdigris and then protecting the coin from air will essentially halt the further development of the verdigris.

[physics-fan3.14]

It's definately verdigris and could have been initiated by PCV (formation of cupric chloride).

 

I've never heard that before. Tell me more, because I'm a little skeptical right now. I thought verdigris was copper carbonate, and I've never heard of verdigris on silver coins.

[BadThad]

I just looked up your coins, I see the 17-S with the obverse MM is very valuable, especially in high grades. Nonetheless, I still recommend the acetone soak just in case that's simple PVC. the sooner you get it off the better! If there's damage underneath the corrosion, there's nothing NCS can do for the coin so you might as well address it yourself and keep your fingers crossed.

 

If the verdigris persists after the acetone, I recommend sending the coins to NCS because they are so valuable. They should easily conserve them both. The only thing I'm concerned about is if NCS uses an acid-thiourea type dip and they come back blast white.....they are known to do that. Personally, I like the original patinas on these coins and, minus the light corrosion, find them pleasing.

 

Good Luck!

[physics-fan3.14]

Thad - how would acetone remove copper carbonate (or copper chloride, as you suggest it is). I thought acetone only worked on organic compounds.

[BadThad]

It's definately verdigris and could have been initiated by PCV (formation of cupric chloride).

 

I've never heard that before. Tell me more, because I'm a little skeptical right now. I thought verdigris was copper carbonate, and I've never heard of verdigris on silver coins.

 

Hey fan! How you doing man?

 

Not sure what you're skeptical about? PVC plasticizers degrade and release hydrochloric acid. The acid reacts with the copper (and silver) creating cupric chloride/silver choride and the characteriistic greenish blue color. Acetone works because the corrosion is surrounded by organic polymeric materials from the degradation. Removing that with organic solvent physically takes the inorganic copper salt along with it. Just basic chemistry and the mechanisms have been well documented and studied....especially by me.

[BadThad]

Thad - how would acetone remove copper carbonate (or copper chloride, as you suggest it is). I thought acetone only worked on organic compounds.

 

You are CORRECT! If the green is only composed of inorganic salts, they cannot be dissolved in acetone nor any other organic solvent.

[jsilver2th]

I find this discussion very interesting. Would your views change if I told you that the coins were never stored in PVC plastic? These were in a leather bag in paper envelopes with an assortment of other coins in a safety deposit for about 35 to 45 years and the last 5 years in storage in extremely dry climate in the same leather old bank bag.

 

I share a concern about the patina and having the coins end up blast white. I have heard that NCS may agree to clean the coins only in acetone if requested. Obviously the thing to do is contact them and ask but I am wondering if any one may have experience with this.

 

I know physics fan that I asked the question before but only had a picture of one coin which was of lesser quality. I worked as a criminal defense attorney for 20 years and one thing you learn if you didn't know it already is that people will many times give you different and/or contradictory answers to the same question. I'm not saying that I expect that you personally would be inconsistent but I might hear different views if I ask again.

 

I have been told that acetone treatment can sometimes produce unexpected adverse results that might contradict conservation goals. I will say I have experiment with acetone bath on other coins of lesser consequence in the leather bag that also have what I will call green crud and generally the results have been good but not what I would call 100% on the more extreme coins.

Although I might get further with repeated bathes.

 

Thank you again for responding and I will try and get back to this post and update when I "make a move."

[physics-fan3.14]

It's definately verdigris and could have been initiated by PCV (formation of cupric chloride).

 

I've never heard that before. Tell me more, because I'm a little skeptical right now. I thought verdigris was copper carbonate, and I've never heard of verdigris on silver coins.

 

Hey fan! How you doing man?

 

Not sure what you're skeptical about? PVC plasticizers degrade and release hydrochloric acid. The acid reacts with the copper (and silver) creating cupric chloride/silver choride and the characteriistic greenish blue color. Acetone works because the corrosion is surrounded by organic polymeric materials from the degradation. Removing that with organic solvent physically takes the inorganic copper salt along with it. Just basic chemistry and the mechanisms have been well documented and studied....especially by me.

 

Ok, I see now. I knew about the PVC leeching out, I've written about that myself. I just never knew that they reacted to form copper or silver chlorides. Interesting. I'm going to have to update my article with that. So the reason we see bright green stuff after PVC contamination is because of the silver chloride. Well, I learn something new every day.

[BadThad]

I find this discussion very interesting. Would your views change if I told you that the coins were never stored in PVC plastic? These were in a leather bag in paper envelopes with an assortment of other coins in a safety deposit for about 35 to 45 years and the last 5 years in storage in extremely dry climate in the same leather old bank bag.

 

I share a concern about the patina and having the coins end up blast white. I have heard that NCS may agree to clean the coins only in acetone if requested. Obviously the thing to do is contact them and ask but I am wondering if any one may have experience with this.

 

I know physics fan that I asked the question before but only had a picture of one coin which was of lesser quality. I worked as a criminal defense attorney for 20 years and one thing you learn if you didn't know it already is that people will many times give you different and/or contradictory answers to the same question. I'm not saying that I expect that you personally would be inconsistent but I might hear different views if I ask again.

 

I have been told that acetone treatment can sometimes produce unexpected adverse results that might contradict conservation goals. I will say I have experiment with acetone bath on other coins of lesser consequence in the leather bag that also have what I will call green crud and generally the results have been good but not what I would call 100% on the more extreme coins.

Although I might get further with repeated bathes.

 

Thank you again for responding and I will try and get back to this post and update when I "make a move."

 

It doesn't look like PVC, it looks like generic verdigris. Apparently, the environment was not completely dry because verdigris cannot form without two essential ingredients, air and water. Leather will actually absorb and hold water so it's a horrible place to store coins. At minimum, these should be stored in Airtite brand holders....after dehydration with acetone.

 

Why pay NCS to soak the coins in acetone? Just do it yourself to dehydrate the verdigris. With a little careful, physical action, you might get some or all of the surface verdigris off since it appears to be very light.

 

If decided to use NCS, make sure you specify they do NOT use acid-thiourea on the coin because you don't want it blast white.

[BadThad]

It's definately verdigris and could have been initiated by PCV (formation of cupric chloride).

 

I've never heard that before. Tell me more, because I'm a little skeptical right now. I thought verdigris was copper carbonate, and I've never heard of verdigris on silver coins.

 

Hey fan! How you doing man?

 

Not sure what you're skeptical about? PVC plasticizers degrade and release hydrochloric acid. The acid reacts with the copper (and silver) creating cupric chloride/silver choride and the characteriistic greenish blue color. Acetone works because the corrosion is surrounded by organic polymeric materials from the degradation. Removing that with organic solvent physically takes the inorganic copper salt along with it. Just basic chemistry and the mechanisms have been well documented and studied....especially by me.

 

Ok, I see now. I knew about the PVC leeching out, I've written about that myself. I just never knew that they reacted to form copper or silver chlorides. Interesting. I'm going to have to update my article with that. So the reason we see bright green stuff after PVC contamination is because of the silver chloride. Well, I learn something new every day.

 

Actually, silver chloride is a white powder. The greenish color comes the formation of copper chlorides. Keep in mind these coins are 10% copper and all silver coins contain {at least} traces of copper.