Was going to post this question in the slab thread since it mentioned touching ancients with bare hands, but I figured this could be a discussion in its own right. I remember way back someone posting on another forum about how touching ancient bronze with bare hands can facilitate their breaking down. I went searching for the post and I happened to find it. Anyone with chemistry knowledge know if this has truth behind it? I always felt that this maybe was just an out-of-proportion exaggeration, but I don't know for certain since I am not very knowledgeable about chemistry in general. I hope I don't come of as fear-mongering or anything. For the record I still have bronze coins from when I started years ago that I've handled and they have yet to break down (others I don't have anymore I've since sold, so those did not break down either.
I have always handled my bronze coins with bare hands and have never had any problems with coin disease or any kind of corrosion, so perhaps this process takes a long time to occur, maybe years after the coins were handled in such a manner.
I think this may affect modern coins rather than ancient. I don't use gloves but then neither do I have a coin in one hand and a doughnut in the other.
Maybe with pure copper coins this is more of an issue. But with bronze alloys I don't think the copper ions are as available to corrode. Keeping them dry is also a big key to stop any new corrosion from happening. Also a good patina I believe may also provide some protection. Not an expert though.
Pishpash is right - this is more of a concern with modern coins. Considering that most ancient bronze coins have a patina, your fingers never actually come in contact with the metal underneath.
Well, being burried and having chemical reactions with the soil already damaged/interacted with the ions in the coin metal or whatever, so that shouldn't be much of a concern 2,000 years later even if you have a coin without patina. The worst I think would happen is the coin might get dark with toning, and then who cares as toning would just add protection. I can see it being a concern with modern coins where the aim is to maintain the original luster, hence turning the owners into obsessed neurotic zombies looking to encapsulate the coin in as many layers of plastic as possible.
The post that you cite describes the action known as bronze disease, described on Wikipedia: https://en.wikipedia.org/wiki/Bronze_disease When I look at the chemical reactions involved, it appears that four Cl (chlorine) atoms are required to form one cupric chloride/cupric hydroxide compound plus two HCl molecules. This means that two of the original four Cl atoms are used up, so eventually the reaction will run out of Cl atoms and stop. (Any chemist here, please confirm.) In bronze disease, the Cl atoms are very difficult to eliminate since they're usually protected by encrustations, and that's why bronze disease is so insidious. But if your ancient AE coin doesn't have bronze disease and has any sort of patina, the amount of NaCl transferred from your fingers to be in contact with the Cu atoms of the coin is tiny and would be unlikely to result in any consequential degradation of the coin. (Again, any chemists here should verify or refute my logic.)
The reaction described in the OP quote does describe the mechanism for bronze disease, but makes a faulty assumption about the bare hand handling of most ancient bronze coins. The chemistry s/he describes assumes that you are touching pure copper or bronze with your bare hands. That is not the case when the coin has a patina. Patina is essentially a non-metallic shell (mainly carbonates and acetates) which forms naturally and shields the elemental copper within from outside contact. It is a conversion of the outer surface of metal into stable non-metallic salts, and these are what protects the coin from destruction while buried in the ground and subject to all kinds of chemical threats. Break through the patina and then bronze disease becomes possible from a number of sources including the transfer of salts by human touch. If your coins have intact patina, you need not fear the threats in the opening paragraph.
Couple of things...first, I'm an organic chemist, so when it comes to metals, I know some, but other people know more (@BadThad are you listening?). Metals are in general reactive, but they can also form protective "skins" that will reduce their tendency to react further. Ancient coins do have a lot of protection, sometimes in the form of dirt that we remove and sometimes as a patina that we may or may not see. Modern coins also have a similar situation, so well circulated coins really do not require gloves to handle them. Uncirculated and proof coins are a separate case. A chemical reaction (inorganic) requires chemicals and water. In the absence of water, the reactions are inhibited, so handling coins with your bare hands is not bad as long as your hands are reasonably clean and reasonably dry.
From one of my favorite all time movies. If only Ben had listened to Mr. McGuire and gone into plastics, instead of Mrs. Robinson, he could have founded NGC.
Don't worry, because you're never really touching anything anyway: "When you plop down in a chair or slink into your bed, the electrons within your body are repelling the electrons that make up the chair. You are hovering above it by a unfathomably small distance." From this webpage: https://futurism.com/why-you-can-never-actually-touch-anything/
Yes, I have heard that both in physics and philosophy (neither of which I REMOTELY know anything about, just a casual user). However, I have always considered testing the theory by asking if the author would mind me swinging a BASEBALL BAT upside their head to see how unfathomably small the distance is, and that it "never touches"... NEXT!
I wear, "special coin handling gloves" if I have to handle one of my coins. However, I stick to looking at them either in a third party slab/ or saflip holder.
