I just noticed a new "spot" appeared on this coin, at around 10 o'clock obverse. I don't think it was there a year ago. There is also a big milk spot near the date. Any help on conserving this coin?
Nope, sorry. PCGS has reportedly offered a modest reward to anyone who could come up with a process to conserve milk spots. It has never been awarded.
Me either. What a shame, it's a great looking coin. If it continues to deteriorate I'd consider a dipping but that brings a few problems of it's own.
10 o'clock looks like a print eating its way into the surface. The spot by the date is of a different nature from those on more modern silver proofs. Your options are: Leave it alone. The print will get worse if it has newly appeared. Acetone bath. If the print is growing due to stuff on the surface, this should stop it. Dip. The appearance of the print and spot should change, perhaps for the better, perhaps not. Sell it. It's a common, easily replaced coin, unless you post a picture of the reverse showing the major doubled die.
You want to try the least destructive methods first. If the 10 o'clock is indeed a fungerprint, an acetone rinse could help and won't hurt. Then, a process I used that helped a proof coin I ordered was to wash your hands, put the coin in a sink and run hot water on it for several seconds, use a dropper to put a few drops of dip (EZest) on the spots and quickly return the coin to the stream of hot water. Rinse with distilled water and place the coin on a soft towel, fold the towel over the coin and press down...don't rub. Good luck!
Sometime I will try that, I used to have some EZest but I don't know what happened to it, I will buy some more, I guess it can't hurt considering how it is right now.