Oy vey... I don't know how else to say this so you'll understand. This isn't about arguing or my opinion, but pressing the OP to do more than simply take my word, your word, or anyone else's word for it. It's very simple, really. It seems quite clear he wasn't familiar with treated coins, so would it not be better for him to take a few moments to confirm the opinions provided him and, perhaps, learn in the process? Believe it or not, I do respect your views, tried to clarify, and even said you're most likely right. Accept this or not, it's your call. What a wonderful hobby this would be if everyone took the word of others are absolute and unquestionable fact instead of doing for themselves.
I don't expect my views or opinion to be taken as fact, but anyone seeing any coin and commenting on it is giving an opinion, what else could you call it. The other person mentioned acid, thats possible also, but Nic-A-Date does grey over time, either way the date area, in my opinion has been treated in some way. In the end the OP has coin worth much more then the 60 cents paid, but now they must find a buyer who will pay for a coin that has been altered by a chemical of some unknown type
I have treated thousands of Buffaloes with and without ferric chloride. Dateless with mintmark examples sell by the roll or bag for about 40 cents apiece. So he got a great deal. I've discovered several 18/7-D's and 13-S types 1 and 2. I've seen these 13-S, type 2's sell for as much as $200 on the internet, despite the disclosure as "acid-treated". Both ANACS and SEGS will generally give a properly treated coin an AG-3 "Acid Treated" designation. I believe most purchasers of these are trying to fill holes or put sets together to sell on ebay to unsuspecting buyers. Occasionally I have bought a 1916 DDO in acid treated condition, just to be able to say that I own one. Whether to submit for grading, to a large part, depends upon the collector's intention with respect to the coin.