Toning Question

[CoinCrusader42]

Here's something I have wondered about for some time.

I was a history major in college, and have very little science background.  However, I assume that coin toning is a matter of oxidation.  If that's true, when does the process stop -- or does it.  Is a beautifully toned coin likely to turn into something ugly years down the road?

Any answers will be appreciated.

 

[AdamL]

Well, I don't know much about science. But I've always been told that it is a process that never stops. You can slow toning down by using good storage methods. but the process still continues.

[KurtS]

I think you're right--toning is just oxidation that's thin enough to interfere with light wavelengths. Simply put, there are two reflections--one off the coin metal and another off the top layer of the oxidation. The two reflections are slightly out of phase and cancel out specific wavelengths of light, producing a color effect. Eventually, when the oxidation gets thick enough, light cannot reflect off the base metal, the phase change is negligible, and the color of oxidation dominates.

Any toned (or bright silver or copper coin) can eventually go through this full process, which is why I'm skeptical on high prices put on toned coins that may entirely disappear (dealers hate me saying this, LOL). Of course, if you store your coins in a vacuum or noble gas, that might prolong the toning indefinitely! 

[longnine009]

I've always heard that toning will "arrest" once it's thick enough and covers the whole coin. From that point on the toning is protecting the coin from airborne contaminants.

[CoinCrusader42]

Thanks to everyone for the information.

 

[justabeginner]

I think longnine is right.. Cause the oxidation layer actually protects the inner metal.... Just like our aluminum roofs.. etc...