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Question About Wood Grain Toning

 
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Author Previous TopicReplies: 9 / Views: 1,512Next Topic  
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 Posted 10/12/2008  12:01 am Show Profile   Bookmark this topic Add Archraz to your friends list Get a Link to this Message
I was just wondering how a copper coin can acquire this sort of toning. When I had seen this type of toning in the past, I just presumed that the coin had been cleaned. Any info about this variety of toning would be appreciated!

Just in case you have yet to see wood grain toning, here is an example:



Image: GreatBritainhalfpenny1920obv.jpg
50.26 KB



Image: GreatBritainhalfpenny1920rev.jpg
53.91 KB
Edited by Archraz
10/12/2008 12:02 am
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 Posted 10/12/2008  12:45 am  Show Profile   Bookmark this reply Add ElleKitty to your friends list Get a Link to this Reply
That type of toning is caused because the alloys in the planchet were improperly mixed. More than that I do not know, but it is very prevalent in the British and Commonwealth coins of that era.
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 Posted 10/12/2008  12:51 am  Show Profile   Bookmark this reply Add Archraz to your friends list Get a Link to this Reply
ElleKitty- ah that is good to know. So this does not affect the grade or value of a coin? I am really glad to hear that this type of toning is not caused by cleaning and retoning.
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 Posted 10/12/2008  01:16 am  Show Profile   Check BadThad's eBay Listings Bookmark this reply Add BadThad to your friends list Get a Link to this Reply
It's also prevalent on early Lincoln cents. Copper coinage is normally a mixture of copper, zinc and tin. Often, the alloy was not well prepared (poor mixing) before it was rolled into sheets and planchets stamped out. During the rolling process, little bits of unmixed zinc/tin get smashed and rolled out, think of a rolling pin on dough with a spot of dye on it. As you roll it, the spot thins and elongates. Now....

This effect happens because the oxidation properties are very different for zinc and tin. Copper is the most reactive, so it takes on a brown patina faster and more deeply than tin or zinc (which actually oxidize white). The streaks result from the copper being less abundant in the streak areas, those area's don't take on a deep brown patina like the higher ratio copper areas.

Whew...hope my rambling makes sense.
Lincoln Cent Lover!
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 Posted 10/12/2008  01:30 am  Show Profile   Bookmark this reply Add Archraz to your friends list Get a Link to this Reply
BadThad- no you weren't rambling at all. That is actually quite fascinating. Thanks!
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 Posted 10/12/2008  08:33 am  Show Profile   Bookmark this reply Add JonS.7070 to your friends list Get a Link to this Reply
Nice coin Archraz!
Bedrock of the Community
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 Posted 10/12/2008  11:50 am  Show Profile   Bookmark this reply Add just carl to your friends list Get a Link to this Reply
On some Copper mixtured coins if such marks are primarily on the reverse it could be due to being in a folder. Not an album, but those type of folders where you can not see both sides. Streaky or grainy effects are sometimes from the glues used to make those folders and they are in a higher humidity location. Look at any such folder and you'll notice the rear of the slots is rather shinny from the glue. Commonly seen on many of the older Lincoln Cents since way, way back Albums hadn't been invented yet.
just carl
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 Posted 10/12/2008  1:45 pm  Show Profile   Bookmark this reply Add Archraz to your friends list Get a Link to this Reply
Thanks for the help, everyone!
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 Posted 10/12/2008  7:57 pm  Show Profile   Bookmark this reply Add Archraz to your friends list Get a Link to this Reply
Thanks for the complements! Believe it or not, I found this one in a 25 cent box.
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