Help Identifying This Coin: Colonial Silver(?)

Welcome!
The Draped Bust quarter of 1796-1807 is 27.5 mm and 6.74 grams. The Capped Bust quarter of 1807-28 is the same weight, and 27 mm, but if I can get around to making some marks on the second pic, I'll show you where I've made myself believe I can see the eye and nose of the Draped Bust Liberty, and maybe the E in the legend. Anybody with me on this?

A soak in acetone may be revealing, but I'll leave to others to best advise how best to do that. NOT nail polish remover, but pure acetone, from a hardware store.

Although I don't hold out much hope for this particular coin, your questions about acetone are good ones. Acetone is an organic solvent that won't harm coins but will quickly dissolve many types of gunk. As Philadelphian said, you want the pure stuff from the hardware store because whatever the non-pure stuff is cut with can harm coins. Sherwin Williams makes a brand named DupliColor that is "100%" acetone (some so called "pure" acetones are only 95% if you read the label). I've been able to buy it at Ace Hardware. In my experience, acetone has dissolved organic gunk pretty quickly so I've never thought about long soaks (others may have different experiences). Don't rinse the coin with anything after the acetone (water can oxidize metals). Acetone evaporates very quickly so your coin will be dry in no time. As always with chemicals, heed all warnings on the label.