Milk Spots Appearing On Bullion Years Later?

That seems like a very peculiar method... does anyone know if it actually works?

You can use a clean and very soft white eraser to clean the dirt if you wish. Don't do that to tiny milk spots though, I heard that cleaning would ruin numismatic value of a collectible coin.

3 or 4 months ago I bought the grizzly coins, exactly look like thehulk's for 38.xx$ each from kitco (spot was 33~34$), cleaned the reverse gently with an eraser, the scratches resulted are barely noticeable. Not all the "spots" were removed because I did not overapply pressure.

I did that because I believed these coins already lost their original numismatic value. Before that I've even ruined a fine cougar using hot water + soap + vinegar combination, when I wiped the solution processed coin with lab wiping paper, the paper became black and the coin was left with heavy scratches. Then I applied some toothpaste on the same coin, no miracle happened but only worse. Because of that I gave up the soda boiling water + aluminum foil idea. On Youtube they used worn circulated silver coins if you have any it might worth a try.

Also, for long-term investment now, I am buying certified 10+ ounce bars exclusively. They are easier to store in the safe deposit box, and sell at a very small premium over spot. maples are attractive for short-mid term profiteering on spot fluctuations, but they are horrible as an investment vehicle at anything more than S+$2, but that is just my opinion.