A bit of a mystery to us, this one is slightly convex with a brooch style clasp on the back but we're not sure if it was originally meant for that. If so, the curvature would seem to imply that it was attached to the shoulder/sleeve. There are no hallmarks but we've acid tested it and it is at least .800 solid silver, according to the test. Interesting no matter how you think about it. I'd do an internet image search but have exhausted my free searches today so it'll have to wait.
Very good to excellent condition, age considered. Just as you see it in the enlarged images, no dents, damage or repairs. As noted, we're not sure if the pin clasp is original. See pictures for weight and measurements.
