A few years ago I bought a pair of 'John Lennon'- type sunglasses with a leather-esque finish on the rims (they're the ones I wear in my profile photo...)
Not long after I bought them I noticed that the faux leather was coming adrift, so naturally I took some small tweezers to them and removed as much of the stuff as I could; this left me with the little problem of what to do about the adhesive that singularly failed to hold the leather in place but now refused to come adrift of the metal rims.
I then decided that they were too much hassle and bought a pair of vintage pince-nez instead. Very nice, but not ideal for everyday wear when they come loose every 20 minutes or so.
Today whilst rummaging around for something entirely different I found my sunglasses again and decided to finish what I began about two and a half years ago.
I began by sorting out the issue that they were hurting my head (the frames being too narrow):
Taking a file to the hinged hooks I removed enough material to allow them to swing beyond 90-degrees; so now they don't press in behind my ears and cause 'discomfort'.
I then turned to the rims themselves. I filled the washbasin with warm soapy water, took a soft brush (something like an old toothbrush would be ideal) and scrubbed at them, having first popped the lenses out. The warm water loosened the adhesive; the brush removed it. In tight places I found that rubbing toilet tissue vigourously against the frames not only removed the adhesive, but polished the metal up nicely too.
After around 20 minutes work I had these:
Frustratingly of course when I look on ebay now all I can find are the same specs without the leather