Have never saw a coin like your 1877. That one should be in a toning book for sure. Pretty. Different. Kinda unique.
Very nice! I’ve had my eye out for a replacement since I sold my last one... nice ones are tough to find.
Depending on what's causing the reaction, a coin can go from rainbow to black soot in months, years, or decades. It's like a colored liquid. There's no way to know when the color will settle (if you don't know the ingredients) but anything that's not a clear solution will eventually settle.