So what would you do with these large cents?

I can tell you this with certainty -- I have had copper pieces (including large cents and 2C) with green patina/verdigris/corrosion that have gotten NO worse in the 30 years I've owned them.

 

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Again, that is simply not true. Oxygen doesn't corrode copper well without high temperatures....

Like I suggested above, if one removes the humidity and/or sulfur (which is very easy to do with an airtite and some dessicant) and the coin will not corrode any worse than it is today. What's worse, is that the patina/verdigris is actually protecting the coin, rather than damaging it -- remove the skin from the coin as you are doing by stripping it with an acidic solution and recolor it actually makes the coin more likely to corrode (particularly if you don't put oil on the coin and keep it fresh).

It's one thing to want to "conserve" your own coins, but there's no reason to suggest someone do something for reasons that simply are not true.

Respectfully...Mike

 

Hmmmm... maybe if you soaked them in black coffee instead of tomato juice, you wouldn't need the Deller's afterwards.

 

Read this Mike:

http://www.digbible.org/restoration.html

The corrosion is oxidation and the the key element required for oxidation to occur, is oxygen. Here's an interesting video showing a penny being dissolved in Nitric Acid:

http://www.youtube.com/watch?v=1oVJ5E8kdWs

If you will pause it when it shows the element structure, you should note there are some O's in there.

Ribbit

 

That may be true, but I don't have any so I use what I have. I will get some Verdigone someday and give it a shot. :thumb:

Ribbit

 

Ps: Humidity is water and water is two parts Hydrogen and one part Oxygen, so does the Hydrogen cause the corrosion or does the Oxygen?

Ribbit

 

Thanks for sending the link, that's a wonderful site!

A few points...

o The site is addressing how to conserve copper that's been buried in the ground, not copper coins like the one shown in this thread (which doesn't look like a buried coin). As I'm sure you're aware, buried ancient coins typically look nothing like the coin in this post, but rather have a completely encased patina like this coin (or even worse, as this coin has already been conserved):



So therefore, the conservation methods for these coins (which typically look like a "hunk of corrosion") should take that into effect, and be quite different from a coin in the condition of the OPs.

o "A thin layer of copper on the coin oxidizes to form a consistent and nonconcealing layer of copper (I) oxide (cuprite) called a patina. Numismatists sometimes refer to this process as "toning." This "dull-looking" patina usually protects the coin from further corrosion though impurities from the air, ground, and sea can cause further corrosion. A good patina should not be removed. If it is removed, the bright, newly-exposed surface will once again oxidize, causing a slight loss of the coin metal." Part of this is correct, and part is incorrect. First off, not all patinas are copper oxide (BTW, copper oxide is red, not blue/green), so that part isn't entirely accurate. The part about patina being considered toning isn't entirely accurate either (sometimes it's toning, other times it's verdigris, and other times it's corrosion). That said, and this is key, the part that is correct is that the patina actually protects the surface of the coin, and once you strip this off, you've got a very-reactive and fresh copper surface (which is why most copper specialists that dip and strip coins apply oil to the surface).

o The following quote explains precisely what I suggested above: "It is important to note that the single most destructive force in causing corrosion is moisture; most of these reactions would not occur without its presence." In other words, take away the water, and you effectively stop corrosion. Silica dessicant is very cheap, readily available, and non-destructive answer to stop corrosion -- and it works.

o "The most damaging corrosion occurs when chlorides and moisture come into contact with a coin, and chlorides are unfortunately quite common in the ground." This is a great quote, and chlorides are something I didn't mention in my original post (my oversight), but similar to sulfur, they are relatively easy to stop from getting to the coin (a kontain or airtite or even a 2x2 all do a great job of limiting airflow and thus chlorine/sulphur), and if you remove water then what little sulfur/chlorine does make its way to the surface will do little to the coin.

Again, you are free to conserve your coins as you see fit, but when you jump to suggesting things that simply aren't true as a justification I will (respectfully) take issue.

Take care...Mike

 

As I understand things, neither -- it is the addition of sulfur (or chlorine) to the humidity that really causes the damage (see prior post for the details).

Perhaps Lehigh, or someone else more familiar with the chemistry of these things can comment -- we are getting near the edge of my understanding of this topic (I'm only an engineer who has been collecting copper for three decades, not a chemist ).

Respectfully...Mike

 

I still wonder if you know what part of water (H2O) causes the corrosion? The video was interesting, in that the penny was submerged and yet it dissolved away and no "AIR" nor WATER touched the coin, but Oxygen was present. :whistle:

Ribbit

Ps: Take issue we me all you want! I love a good argument.

Ps: On your last comment, I've noticed that after I clean a copper, if I don't coat it right away it will start corroding again, and there are no sulfides involved. Furthermore, sulphates are what cause the copper to turn brown (patina) and that's a form of sulphur.

 

The 1807 Comet is already cleaned (polished) and retoned, so it can't be hurt by doing it again. That is why there is active spotting on it - once you remove the natural surface you expose it to the elements anew and it can spot up over time.

 

It was the nitric acid that dissolved the coin, not the air or water, per-se.

It is my understanding that there are sulfates in the air normally. That and humidity/water combine to be reactive to copper. Thus if you remove the sulfates/cholrates and/or the humidity, you've essentially stopped the corrosion.

 

Hi Rick! What makes you think the first coin was polished? I must admit your comments are confusing to me -- and of the two coins posted, it is the second one that looks much more like it's had work done on it already. Respectfully...Mike

 

There's something odd about this whole experiment...

That "penny" has the uncrowned portrait of Queen Elizabeth (I like to call it the grandma head), and when they started using it in 2003, the 1 cent coin was copper plated zinc or multi-ply plated steel (with .045 copper content).

 

Mike desiccants are great but depending where you live might not be enough , what about Intercept Shields , these are supposed to neutralize all the sulfides that are doing the damage , just a suggestion .
rzage:whistle:

 

While I do use IS products (the red double-row boxes) in my SDB, I have no long term experience with them so can't really comment on their efficacy. But the theory sounds very good -- good enough for me to buy their product at least.

That said, I doubt there's anyone on this forum that lives in a significantly more humid environment than I do -- on the west coast of Florida about 3 miles from the water and right now outside it's 47 degrees with 82% humidity -- and my coppers which spent most of their adult lives without the protection of activated dessicant (but enclosed in 2x2's and some in kontains) have miraculously survived decades without getting any worse.

Just some food for thought....Mike

 

I wondered if they were because of the weird reaction it had into the experiment and the professor didn't know about the zinc center. :goofer: When the mixture had that brown look to it, that's when it had reached the zinc and started dissolving it.

Ribbit

 

OK can we get back to the original question about what to do about the two coppers? I thought it was going in a good direction then it went to the chemistry of corrosion the question is what to do about conserving the two coins pictured. I would be interested in what should be done or what is done to them. Ice

 

I thought it still went in a good direction. Knowledge is power and there's nothing better then a good debate. (I'm still grinning over Toad's Beefaroni comment... lol.)

As for your question, personally I think there is only one answer for these historic and valuable coins... NCS then NGC. You'd be foolish to attempt anything on these coins yourself.