Silver Quarter Yellowing

Silver reacts with sulfur present in the air (NOT oxygen), and begins to "tarnish".

However, the word "tarnish" usually brings up frightful imaginings of someone scrubbing away at a piece of silver to strip off the whole surface layer - so to avoid this connotation, we like to call it "tone". Tone is harmless (it won't progress to the point where the coin flakes away).

The typical progression is yellow, then dark blue, then black. This is because silver sulfide refracts light differently than the silver underneath - imagine rainbowy oil on water. The water is the silver, the oil is the silver sulfide. Many colours are possible (like with the oil), but to preserve them, the coin must be placed in an airtight container. Otherwise, they will be shortlived as the sulfide layer thickens and changes.

Your coin will probably start looking like burnt toast before becoming completely black, but even minor chemical changes can upset this process, and every silver refinery does it a bit differently. Morgan dollars are well-known for turning rainbow colours - I have a low-purity Mexican peso (10% silver) that's almost green. A cleaned silver coin of mine started to turn orange, and a silver half dollar my dad saved as a kid turned a dark, lustrous red and blue. So who knows?

Or, if you don't want this to happen - put it in a little capsule. It'll stay off-yellow forever.

Getting rid of this yellowing will involve cleaning it, which will make it worth less.

I tried this too when I was starting out - fresh out of a chemistry course, I thought... "There's got to be a way to flawlessly remove the sulfide without touching the silver!"

There might be, but all the methods that can be done outside of a laboratory will be obvious, even to you (after some practice and once you see other cleaned coins). The problem is that you can't unclean a coin, so if your taste changes you're out of luck (and almost everyone else won't touch it).

However, since 1964 quarters are so common - an attractively coloured one could actually be worth more than a plentiful shiny one.

Your best bet is to enclose it. 2x2s are fine, if you mean the cardboard holders. The clear plastic dual-pocketed flips won't do it. You can buy these at any coin store. If there's none nearby, there are lots on the Internet too.

Leave the coin alone because cleaning the coin will ruin any value it may have. Look at it this way toning is very collectible to many people and nice toning usually commands a premium over and above what it numismatic value may be. Who knows you may learn to appreciate toning and if not I'm sure you can make a trade with someone for the same coin not toned.

Fortunately silver 64 quarters are pretty common so if you're wanting one in BU or so there's plenty out there.

Rick