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Early_Milled_Latin_America
Posts: 6,436 ✭✭✭✭✭
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Early_Milled_Latin_America
Posts: 6,436 ✭✭✭✭✭
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silver corrodes, just not as easily as other things. I can completely dissolve a silver coin or even a gold coin in aqua regia, for example.
Agree. silver can corrode, esp if alloyed with copper or other metals that can also corrode.
Tarnish is a form of oxidation, as is corrosion. And we know silver can tarnish...
What is the best cleaning method for silver coins with corrosion or verdigris? Or is it best to have say NGC do it?
How bad is the corrosion? Are you sure it is verdigris and not PVC? Verdigris is typically a copper problem.
Got pix?
Acetone will take care of PVC. Not much you can do about corrosion. It is usually etched into the metal. You can treat verdigris on copper with Verdigone (now VerdiCare). But you may have trouble finding it. A friendly forum member may help you out.
I doubt the smart thing is to send it to a TPG for conservation. OTOH, if it is very minor, perhaps. I'd turn to PCGS before NGC.
Lance.
If you're looking for a coin restoration service I recommend PCGS. 😇
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I agree with this. I was quite pleased with the two items I have had conserved with PCGS.
Just get some sandpaper and rub that tarnish off!
Thanks guys if ever it turn out to be something will send it to PCGS will they then slab it?
Chemically, silver corrodes quite easily! Look at old silver platters and silverware. It’s actually less reactive when alloyed with copper. Every beautiful (and ugly) toner you see posted here is a result of silver corrosion.
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If it's genuine, sure...PCGS will slab it. Conserved or not.
But I think you're asking if it might straight-grade after conservation. If PCGS agrees to conservation (not always) and the results are acceptable to PCGS then yes, the coin could straight-grade. But anything is possible, including other problems that would preclude it.
Lance.
edited to add: Sorry...I see you are talking about a holed ½ Reale. LOL. Not much chance of a straight grade.
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Toning is corrosion. There is absolutely no difference. Metal doesn’t “decay from within.” It reacts chemically, at the surface. Sulfur compounds are particularly fond of silver. Once silver compounds form, the process, as far as coins are concerned, is more or less irreversible.
Dipping or “restoration” simply means stripping away the silver compounds, usually with an acid. The thin layer of silver oxides or silver sulfates are removed, thereby taking away a bit of the original surface, the original flow lines (luster) and leaving behind white, raw, chemically “hungry” surfaces that are easily attacked by new environmental contaminants.
A thin layer of natural patina actually protects the coin to some degree from further chemical reactions.
Most people think too much “dipping” destroys luster. In my opinion, it’s the corrosion that does the actual damage. Dipping only exposes damage that has already happened.
I proved this to myself by leaving lustrous coins (bullion-value stuff) in a popular dip solution for several days. The luster wasn’t impaired at all, at least as far as I could tell.
Thanks that makes sens.
Gold is almost chemically inert. It will stay beautiful and lustrous for centuries, even in the ocean. Our US gold coins can form a beautiful patina, but it’s a reaction with the copper in the alloy.
As stated above, tarnish is corrosion.... it is the chemical degradation of metal due to interaction with environmental contaminants. In the case of silver (AG) it is commonly sulfur derivatives, but others can also be present. Heat, humidity will accelerate the process. Removing tarnish will also remove the silver that combined with the contaminant. Whether ugly or colorful, tarnish is still environmental damage to the coin. Cheers, RickO
Certainly. Have you ever seen any of those US-Philippine silver issues that got dumped in Manila harbor to keep them out of Japanese hands? They're pretty eaten up. Granted I think those were .90 fine not .931 as the OP specified but I can't seen why it would make much difference.