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8 Reales 1770 Potosi - Bubbles?

 
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Author Previous TopicReplies: 11 / Views: 433Next Topic  
Valued Member
Germany
121 Posts
 Posted 12/02/2021  12:48 am Show Profile   Bookmark this topic Add DirtyHarry to your friends list Get a Link to this Message
Hi,
the following coin was auctioned at Heritage Europe many years ago. Do you believe these bubbles are the result of surface corrosion? How can these be formed?

Thanks a lot,



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United States
42716 Posts
 Posted 12/02/2021  04:31 am  Show Profile   Bookmark this reply Add John1 to your friends list Get a Link to this Reply
( I'm no pro, it's just my humble opinion )
Searched 6.5 +/- Million Cents Since 1971
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21924 Posts
 Posted 12/02/2021  06:20 am  Show Profile   Bookmark this reply Add Spence to your friends list Get a Link to this Reply

Quote:
How can these be formed?


@dh, we have several experts on these who stop by CCF on occasion. While we wait for their informed replies, I would only add that such bumps could be the result of striking coins with corroded or rusty dies. Such bumps are also sometimes found on cast fakes.
"If you climb a good tree, you get a push."
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"The danger we all now face is distinguishing between what is authentic and what is performed."
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Valued Member
Germany
121 Posts
 Posted 12/05/2021  1:09 pm  Show Profile   Bookmark this reply Add DirtyHarry to your friends list Get a Link to this Reply
Hi Spence, thanks. Yes I agree!
In this case, I believe the coin to be authentic.
The obverse suffered the black stain corrosion I so much hate and frequently found on Potosi silver coins (Silver impurity-related perhaps?) and was therefore cleaned pretty harshly.
The reverse seems quite good, but the bubbles are present on such a number I never saw anything quite like it.
I am not an expert on these, however.

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United States
2438 Posts
 Posted 12/07/2021  2:28 pm  Show Profile   Bookmark this reply Add thq to your friends list Get a Link to this Reply
Intense heat can cause bubbles like this (blowtorch or house fire, eg), especially if the coin is plated. Possibly seawater corrosion, but not much damage is visible other than the bubbles, and the damage is on one side. Possibly casting bubbles, though there are far more than usually seen. The coin looks correct otherwise.

I have a few Potosi 4R cobs (1765-1771), which are as black as coal. I suspect that they are Seville Harbor recovery coins. I cleaned a couple of them, and they look like the shield side of this 8R. Here are two of them, an uncleaned one on the left and a cleaned one on the right.


"Two minutes ago I would have sold my chances for a tired dime." Fred Astaire
Edited by thq
12/07/2021 2:44 pm
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1632 Posts
 Posted 12/07/2021  6:24 pm  Show Profile   Bookmark this reply Add realeswatcher to your friends list Get a Link to this Reply
Looks to be some sort of heat or chemical damage.
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1527 Posts
 Posted 12/07/2021  10:59 pm  Show Profile   Bookmark this reply Add colonialjohn to your friends list Get a Link to this Reply
Alloy Errors:
Gas Bubbles
Definition: On rare occasions a pocket of gas forms and expands when a planchet is struck. The heat generated by the strike is deemed responsible for the gas expansion. The expanding gas pushes up the overlying metal, producing a rounded bulge with soft borders. If the roof remains intact, the error is designated an "occluded gas bubble". If the roof explodes from the internal pressure, we call it a "ruptured gas bubble".

If the roof is thin, it will flex or it will be left with a dimple when the tip of a toothpick is pressed into it. If the roof is thick, it may not yield to pressure.

By definition, occluded gas bubbles are generally restricted to solid-alloy issues. While gas bubbles are sometimes seen on clad coins, these always turn out to have been caused by heat applied externally outside the Mint. Occluded gas bubbles should not be confused with blistered plating, the latter being an affliction restricted to copper-plated zinc cents.

So if genuine some RARE form of heat generated striking event - yes unusual making the coin a suspect forgery of casting but it appears genuine. John Lorenzo (Numismatist).
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 Posted 12/07/2021  11:11 pm  Show Profile   Bookmark this reply Add jgenn to your friends list Get a Link to this Reply
If you own this coin can you at least give us it's weight? Does it have the correct edge? Or do 8 reales with funny surfaces get an automatic pass on basic authenticity checks now?
Edited by jgenn
12/07/2021 11:20 pm
Valued Member
Germany
121 Posts
 Posted 12/12/2021  12:43 pm  Show Profile   Bookmark this reply Add DirtyHarry to your friends list Get a Link to this Reply

Quote:
If you own this coin can you at least give us it's weight?

Hi jgenn, sorry but I am not the owner. It was being offered by a private individual on a web marketplace and I was very curious about it. As I said I am not an expert on these coins but I have collected them for years and this mint and era combination is of great interest to me.
Weight info is missing from the article and the only record I could find online from this coin, when it was auctioned by Heritage Europe (17.05.2013, Auction 38 - Session 4), shows no weight either.

Quote:
Does it have the correct edge?

This is all I have from the article:


Quote:
Or do 8 reales with funny surfaces get an automatic pass on basic authenticity checks now?

I don't believe to have claimed such thing, but they shouldn't, of course.


I add another detailed picture from the obverse. I still doubt this is a cast fake, but this is just an impression far away from certainty.

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 Posted 12/12/2021  1:28 pm  Show Profile   Bookmark this reply Add jgenn to your friends list Get a Link to this Reply
Thanks for adding those additional photos and details.

To me, the coin looks struck, not cast. But that in no way is a strong vote for authenticity. Without additional measurements like weight and specific gravity, I don't believe we have enough information to determine if it might be regal.

The edge photo does show an overlap -- too bad we can't see the opposite side.

One other explanation for the surface bumps would be from a die with rust pitting. That could account for the appearance of the anomalies on just one side.
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 Posted 12/13/2021  2:57 pm  Show Profile   Bookmark this reply Add jfransch to your friends list Get a Link to this Reply
I am just a collector and not an authenticator but my vote is those are casting bubbles and I would guess a specific gravity test will show less than 90% silver. I have seen many coins struck from rusted dies and they don't look like this one and I have seen too many cast coins that share this "bubble' anomaly. There are bubbles it appears on the shield side (which is the obverse) located around the "8" and up into the "ET". If you are considering buying this coin, I suggest waiting for a nicer example to come along.
"Suppose you were an idiot, and suppose you were a member of Congress. But I repeat myself."
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Valued Member
Germany
121 Posts
 Posted 12/13/2021  10:53 pm  Show Profile   Bookmark this reply Add DirtyHarry to your friends list Get a Link to this Reply
First of all, thanks to everyone for your replies and most importantly for your time and knowledge, which is invaluable to me.

Quote:
If you are considering buying this coin, I suggest waiting for a nicer example to come along.

Thanks a lot jfransch! But no. Besides its oddities, the coin was awfully expensive. However I am very intrigued by its surface.

Quote:
To me, the coin looks struck, not cast.

I Agree!

Quote:
Without additional measurements like weight and specific gravity, I don't believe we have enough information to determine if it might be regal.

Sadly weight and dimensions info is lost. And the item has already been either sold or withdrawn.

Quote:
Looks to be some sort of heat or chemical damage.

Yes, fire or chemical damage are good explanations.
Regarding this, I would like to post another coin somewhat close in resemblance I have seen online before.
It's not the same of course and it doesn't have so many bubbles but some of them look quite similar.
(Please note the NGC label)





Thanks again!
Best,
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