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Author Topic: Red Spots on Coins  (Read 2881 times)

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Fiorenza21

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Red Spots on Coins
« on: September 23, 2009, 09:48:10 am »
Maybe this has been asked before.  What kind of corrosion are the red spots that are sometimes found on coins?  These are a bright red/ orange colour.  I have a few coins from the middle east with this red crust.  I thought I might be able to easily grind it down but the stuff goes deep into the coin.  Any suggestions on how to clean these?

Fiorenza21

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Re: Red Spots on Coins
« Reply #1 on: September 23, 2009, 10:05:38 am »
Ah, it seems there are previous topics on the subject!

Offline areich

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Re: Red Spots on Coins
« Reply #2 on: September 23, 2009, 10:06:04 am »
A picture would help but red spots can mean encrustations that have been reduced to the level of the coin.
I suppose you're not talking about red sand (often called a desert patina and sometimes faked with sand glued to the coin).

Andreas
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Fiorenza21

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Re: Red Spots on Coins
« Reply #3 on: September 23, 2009, 10:26:01 am »
A picture would help but red spots can mean encrustations that have been reduced to the level of the coin.
I suppose you're not talking about red sand (often called a desert patina and sometimes faked with sand glued to the coin).

Andreas

It's not the desert patina.  From previous topics I just viewed the red spots are referred to as boils and have been identified with advanced bronze disease.  It seems all I can do is leave the spots as they are.  So far I've seen that trying to remove a red boils leaves nothing but a nasty scar.  One of the coins was a decent Constantius II Gloria Exercitus with full Antioch mint mark.  A rather common coin, but it would have been flip-able if the red boil wasn't directly on Constantius's cheek!

Offline casata137ec

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Re: Red Spots on Coins
« Reply #4 on: September 23, 2009, 10:39:15 pm »
Those things suck! The only thing I have ever removed them from successfully were white metal billon coins. The best you can do is manually reduce them to around the level of the surrounding flan and call it quits....or just leave them be!

Chris
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Offline simmurray

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Re: Red Spots on Coins
« Reply #5 on: September 24, 2009, 04:21:43 pm »
I have a batch with 'Red' lumps - one is producing green BD.  They are now all soaking in Gringgots BD treatment.  My friend who is an home chemist suggest diluting citric acid and thiourea in distilled water.  Soaking the coins in this may help(he was not too sure what would happen)

No idea if that would work, not even sure where you get thiourea from

Steve

Offline casata137ec

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Re: Red Spots on Coins
« Reply #6 on: September 24, 2009, 06:42:20 pm »
The main problem with these coins is that the red crud isnt simply "on" the flan...quite the opposite, they are by and large "in" the flan, meaning that if you delete the boils you now have divots in your coin. Imagine pulling out a tree stump...

The pic below is a nab I took too far...it is hard to tell from the scan, but the divot is about a mm below the actual flan and just keeps going. This started off as a red boil about a mm and a half high...

Chris
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Jarvis Wei

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Re: Red Spots on Coins
« Reply #7 on: November 14, 2009, 09:59:13 pm »
Possibly known as red plague, formation of red Copper(I) oxide.
This might happen when there is silver content along with copper at a high moisture and oxygen environment, a galvanic corrosion which leads to 'pitting'.

I suggest to grind it down to level with the coin.

 

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