It's the type of clasp popular in Victorian to Georgian era, strung with multiple strands of seed pearls or possibly facet-cut garnets - you know the look. Often they were made up in pairs, one for each wrist. I've had a stash of antique clasps for decades, thinking I'd do the restringing and take them back to their wearable glory, but projects do get put aside. Time to pass this one along. The little hand painted portrait plaque is actually porcelain, though it has a look of a little kiln-fired enamel. Keep in ming, it's only 3/4" x 5/8" oval and to the naked eye, it's impossible to see any very slight imperfection. Full measurements are noted on the photos.
Very good to excellent condition for age and type, no real loss nor damage and would be charming made up again as a wearable bracelet. Dates mid-1800s or earlier. I didn't test the backing but did the face because of lack of any tarnish. It does test 10k gold, so at least that part is. No chips nor loss to the little portrait porcelain.