@Lin one quick test is to make a stripe with (a corner of) the bracelet on a white sheet of paper. (you don’t need to press hard, and pressing hard would tear up the paper anyway) If the metal from the bracelet leaves a line that looks similar to that of a regular pencil, then that could point to it being silver. The test is not conclusive though (f.i. lead leaves a grey line too). If you really want to be sure you should perhaps buy one of those little silver testing kits that are readily available.
edit: a pic will prolly say more than my jibberish. Left isn’t silver (i think it’s Alpaca), while right is Sterling silver.
The use of an XRF has become popular. You might have a jeweler in your area that could test both sides of the bracelet. They might charge you for it though. If you do, record the percentages and let us know.
I could see a couple of those marks (although I didn’t know what they were), but the line on the edge at the right was nearly impossible to see until I took a pic and blew it up. This thread taught me quite a bit, thanks!
