I have a fairly large gold ring with squared-off edges both inside and outside. I would like to round over both the inside edges to make the ring easier to get on and off – it’s a snug fit but wearable, but uncomfortable especially to remove.
I’m thinking a small, very fine-grain round or curved rasp very lightly and gently applied, but even that might leave marks. Maybe some wet-dry sandpaper wrapped around a dowel? I know gold is soft but I’ve never tried to shape any before. If it makes a difference, the ring has three colors of gold, white, yellow and rose, and the white and rose are the ones that would be affected.
I’m not concerned about reducing the value of the ring because I’ll never sell it. I’m only concerned that I might do something that would leave a visibly ugly mark.
Use a fine file or sanding to get it close to what you want, then begin polishing it with very fine grit paper, at least 500 grit, maybe 1000 or more to get it smooth and shiny again. If you had something like a Dremel tool you could do this quite easily and use an actual buffing pad to finish it off. Those tools cost very little, there’s one for 10 bucks at Harbor Freight. It doesn’t come with buffing compound but toothpaste will do the job.
There probably are file gauges of some kind, but even though I have dozens of files I have no idea how they are measured. A nail file is fairly fine, might do the job, you wouldn’t want something much rougher than that. At the beginning you could remove a lot of metal fast with with a coarser file, but it probably won’t take long until you need a finer file to avoid taking off too much. The sandpaper on a dowel may be better to fit the shape inside the ring.