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 Replies: 9 / Views: 1,605 |
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Pillar of the Community
Canada
1984 Posts |
i just pulled out a number of the old zinc prime ministers medals given out by Shell years ago. They are in poor shape after having sat in a slightly damp environment for a long period.
Is there any way to remove the white corrosion? In this case I am not too concerned if the medals turn out to be "cleaned" as they are of little value and, if the corrosion is not removed, they are of no value.
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Pillar of the Community
Canada
3167 Posts |
 Good question. I have quite a few with this as well. |
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Moderator
 Australia
16867 Posts |
Zinc is a particularly unsuitable metal to make medals out of; this apparently did not stop them.  The white powder is mostly zinc oxide. Any acidic cleaning agent strong enough to remove it will be strong enough to attack the underlying metal as well. If the white coating is fairly thin and even, it should come off fairly easily. But if there are white blotches, it's likely the underlying metal already has pitting before you begin, and removing the white stuff will reveal the ugly pits. Don't say "infinitely" when you mean "very"; otherwise, you'll have no word left when you want to talk about something really infinite. - C. S. Lewis
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Pillar of the Community
 Canada
1984 Posts |
Thanks! I know I will get some pitting but I will follow your cue and try vinegar on one and see if the acid removes the powder. There is enough oxide on them to make them unpleasant to touch. There is also some visible distortion of the underlying medal. I suspect that these are a write off but it is worth a try.
For those with these medals, I had four partial and full sets all stored in the same drawer in the basement. The three sets that came in the original cardboard holders are all corroded. Obviously the cardboard accelerated the corrosion. he set stored in the walnut display case is not corroded. Strangely, of the 50 odd medals that I have, all but one have lost the brass/gold plating and are now the colour of zinc. One for some reason (perhaps heavily plated?) remains brilliant brass in colour.
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Moderator
Canada
10463 Posts |
I would blame the humidity, more than the cardboard. The cardboard was simply a mechanism to capture and retain moisture...
"Discovery follows discovery, each both raising and answering questions, each ending a long search, and each providing the new instruments for a new search." -- J. Robert OppenheimerContent of this post is licensed under a Creative Commons Attribution-NonCommercial 3.0 Unported License. See: http://creativecommons.org/licenses...0/deed.en_USMy eBay store
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Pillar of the Community
Canada
1984 Posts |
I am actually pretty pleased with the outcome. I soaked the medals in vinegar for a few hours and most of the corrosion was removed. The medals are obviously still in terrible shape but at least they are now not repulsive to the touch. The details underneath are actually still pretty intact....... Before:  After:  The before actually looked worse in hand than in the photo and the after actually looks better. Edited by Smallcentguy
05/09/2013 9:11 pm
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Pillar of the Community
Canada
3167 Posts |
Nice! I will have to try it. Just regular household vinegar?
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Pillar of the Community
Canada
1984 Posts |
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Pillar of the Community
Canada
2805 Posts |
Vinegar will corrode zinc and produce tiny hydrogen gas bubbles. If you want to have fun with this, try finding a zinc cent and harshly scrape it on a brick or similar until a ring of zinc is revealed around the design. Leave it in vinegar for a long enough time (two weeks?) and the zinc will degrade into zinc acetate (black flakes), allowing you to peel off the extremely thin copper layer with care and do whatever you want with it - I'd try gluing it to things.
However, I can't recommend the usage of vinegar on unoxidized but dull zinc medals, as they will just corrode and get pitted very fast. Finding a chemical process that would attack zinc oxide but not zinc is beyond my current knowledge, so beware!
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Pillar of the Community
Canada
3167 Posts |
Cool! Thanks! Gotta try that  |
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Replies: 9 / Views: 1,605 |
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Posted 05/08/2013 10:08 pm
