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ozjohn

1917 Halfcrown

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Vickysilver - in my opinion the coin graded MS64 is not softly struck but shows significant signs of wear (in all the obvious places). If you believe the coin is softly struck, then I'm sure you must be correct!

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Vickysilver - apologies having a studied a little closer, I think you are right about it being softly struck.

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14 hours ago, youliveyoulean said:

Re Sword:- "there is slight weakness at the top left of the shield which has almost merged with the crown. I did debate with myself if I should wait for a better struck example. However, I decided that since most 1917 are weak in that area and I might have to wait quite a long time to get fully struck example."

This is certainly true for the 1917 halfcrowns in particular.

The whole series, in fact.

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I had a good look at the coin in question especially the black around some of the lettering. The black indicates to me that it is silver sulfide ie normal tarnish with a bit of dirt thrown in as verdigris would be green as it is copper based. It seems that the jury is out on verdigris on .925 silver coins. If you have any examples of copper based verdigris on sterling silver coins perhaps you would  like to post some pictures illustrating this. I hear what you are saying but yet to be convinced.

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Not to enter into this fray, but I wonder if the oxidation that occurs in PVC holders that is green in colour and sometimes called "green slime" is technically verdigris - this occurs on copper and silver, not gold that I've seen.

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I have conducted some research regarding the possibility of verdigris effecting modern sterling silver coins. I contacted a well respected Australia dealer in British and Australian coins who  has been trading for several years and has never encountered this issue. A paper which suggested that leaching of Cu from coins could take place over several hundred years. but not with modern coins and in addition no evidence has been presented by youliveyoulean to support his assertion. The only conclusion I can arrive at is this is b@@ @@@@t  and should be ignored.. I rest my case. 

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Sorry to drag it up but I acquired a 1902 crown the other day which did have a few green spots, but nothing that had fully taken root.

I agree that verdigris on sterling silver coins is unusual (I couldn't recall any examples barring my recent purchase) and probably would be due to contact with other infected coins rather than environmental factors.

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I hear what you say but what you observe does not mean the Cu is leaching from the silver coin. It is most probably from external contamination. Alloys of metal form electron bonds between the component metals that introduces  chemical stability to the alloy This is what makes the leaching of the component metals unlikely. I suspect this is true for even 50% silver alloys used after 1920. For example dental amalgam which is basically an alloy of silver, mercury & copper (50% Hg, 30% Ag, 14% Cu plus a little Sn thrown in).. If this alloy leached mercury in any appreciable amount we would all be mad or dead.

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What does the remaining 7.5% of sterling silver actually consist of?

Edited by Peckris

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Mostly Cu. However to separate the Cu from the Ag you would need something to break the bonding of the component elements that are sharing their valency electrons. For example oxygen blown thru the molten alloy that would turn the component metals into their oxides which could then be separated. The original assertion was that a coin with some black marks on it was affected by verdigris. The first thing is verdigris is green not black. Green Cu compounds indicate that they are cuprous (valency 2) not Cupric (valency 3) which are black. Verdigris is associated with cuprous Cu compounds as it is green. Any deposits on sterling silver coins evenif they were Cu based would not be verdigris Ag oxides and sulfides are black and these are what you normally find on tarnished (toned) silver coins. I think my chemistry is ok but it has been a long time since I have had anything to do with it.

I also contacted a Sterling and Currency in Fremantle a coin dealer who has been in the business for several years on this question for a practical opinion. In their opinion they had never seen verdigris on sterling silver coins. 

I also found a reference that Cu could leach from very old silver coins but here they were talking about coins several hundreds of years old and I do not think 1917 qualifies for that age.

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A couple of typos: Should read: Any BLACK deposits on sterling silver coins even if they were Cu based ………………..

I also contacted Sterling and Currency …………. No a

Sorry if there is any confusion caused.

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also could be an imperfect mixing technique where there are "pockets" of higher CuNi content rather than perfect mix all over

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Provided that the silver and copper metal are properly mixed to form the alloy then 'traditional' verdigris as found on copper is not going to happen i.e. crusts of green material eating into the surface and ruining the coin. However, the copper in the alloy will still be attacked by air/water and the same copper compounds that comprise verdigris will still form. The difference is that the low concentration of copper in the mix means that clusters of green won't occur but an overall general green sheen across the coin is possible. The desiity of this may vary depending on whether the silver has also reacted with air to form oxides/sulphides i.e has toned, and the pattern of this toning across the coin.  

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I suspect the RM is competent to make sure their silver alloys are correctly prepared for coin making. They have been doing it for a long time.

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20 minutes ago, ozjohn said:

I suspect the RM is competent to make sure their silver alloys are correctly prepared for coin making. They have been doing it for a long time.

They were spectacularly incompetent when changing to a 50% alloy in 1920.

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A poor choice of metals to replace sterling silver perhaps. They did not hit on the right alloy until about 1927.I think I remember that the early 50% silver coins were "treated"to migrate Ag to the surface to improve their appearance. This can be seen when they wear and take on a distinct "coppery"look. Even with the increased copper in these coins I have never seen green verdigris form on these coins even when they have been lying forgotten in a draw for years. In Australia, where these coins were stored we experience much higher humidity than the UK which is conducive to the formation of verdigris. No verdigris was found on these coins.

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Although I agree that verd on sterling silver coins must be very rare indeed, it can sometimes be found on 0.5 silver coins. In fact, it is one thing I particular look out for when buying post 1919 George V. 

Uneven metal mix causing verd has also crossed my mind as a theoretical possibility. I am not saying it really happens but just as a possibility. As I understand it, uneven metal mix is not that uncommon with bronze coinage and this results in streaky toning. 

Edited by Sword

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George V coins with Verd

img - Copy.jpgimg (1) - Copy.jpg1 - Copy.JPG

 

Even a "green spot" on a sterling silver coin is much more likely to something else than verd I think.

 

 

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Sword, thanks for the images. The 50% Ag coin certainly looks like verdigris. As I said in all honesty I have never seen it before and I have been collecting coins on and off since the mid 1960s.  I agree completely with you regarding sterling coins the chance of verdigris is very unlikely. I notice one of your coins has been graded by CGS. I thought they were supposed to reject coins subject to corrosion or did the verdigris form after slabbing?

Just a question do the green spots pit the coin as what happens with copper and bronze coins or is it restricted to the surface of the coin?

Edited by ozjohn
Extra question, typo

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Hi Sword,

I received this coin the other day from Pennycrown  a 1931 florin  a common date I did not have. Anyway in light of our discussions I carefully examined the coin and noticed a slight greening around the V in George V which looks like the start of verdigris forming on the coin. It doesn't seem to have damaged the coin and I will try some metho on it to remove it. As I said I have not see this before but there is always a first time  and I will keep an eye open in future.

I tried to remove it with metho and it completely went with out any apparent damage to the coin..

img155.jpg

Verdigris.jpg

Edited by ozjohn

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7 hours ago, ozjohn said:

Sword, thanks for the images. The 50% Ag coin certainly looks like verdigris. As I said in all honesty I have never seen it before and I have been collecting coins on and off since the mid 1960s.  I agree completely with you regarding sterling coins the chance of verdigris is very unlikely. I notice one of your coins has been graded by CGS. I thought they were supposed to reject coins subject to corrosion or did the verdigris form after slabbing?

Just a question do the green spots pit the coin as what happens with copper and bronze coins or is it restricted to the surface of the coin?

The first two wreath crowns were sold by London Coins but were not graded by CGS. The auction descriptions did mention verdigris.

I think well-established verd on 0.5 silver must eventually pit the surface. 

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1 hour ago, ozjohn said:

Hi Sword,

I received this coin the other day from Pennycrown  a 1931 florin  a common date I did not have. Anyway in light of our discussions I carefully examined the coin and noticed a slight greening around the V in George V which looks like the start of verdigris forming on the coin. It doesn't seem to have damaged the coin and I will try some metho on it to remove it. As I said I have not see this before but there is always a first time  and I will keep an eye open in future.

I tried to remove it with metho and it completely went with out any apparent damage to the coin..

img155.jpg

Verdigris.jpg

When viewing the photo on my tablet which has higher resolution compared to my laptop, I think there are green spots on quite a few other places also. E.g. below the mustache, around the ear, neck, R and E of Rex etc. I am not saying they must be verd spots however.

 

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Hi Sword,

Thanks. I had another look under a X10 glass and it seems to be clear of any green color. Perhaps because I cleaned the whole surface both sides with metho which seems t remove it. No sign of pitting where the green was. The space around the R & E of REX is a black color suggesting silver sulfide.

Hi Peckris,

Received 1915 penny in good condition today. Nice coin for a good price thanks.

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12 hours ago, ozjohn said:

I think I remember that the early 50% silver coins were "treated"to migrate Ag to the surface to improve their appearance. This can be seen when they wear and take on a distinct "coppery"look.

I believe the planchets were dipped in acid to remove some of the copper from the surface.

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Yes, referred to as "blanching". Most green oxidation such as Sword showed seems to have a PVC component and in my experience there is a good chance of removal with the blot method of acetone with the high nap white cotton towel.

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