My Purchases From A Labor Day Sale On Coins.

One plausible explanation would be that the Half Cent may be bent ever so slightly and not enough to notice. Try laying it on a perfectly flat surface such as mirror and see if a sheet of paper slides under with little to no effort without pushing the coin. As for the acetone I've had 90% success at removing haze, glue, paint and such. Each varying in the amount of soak time. Your's I'd soak overnight and progress by a few hour increments as needed. It won't however remove the toning or milk spots like on that half dollar.