Antique French Kiln-fired Enamel Portrait Miniature, 18k Gold on Silver Jeweled Frame Brooch

Splendid mid-1800s French jeweled brooch, silver with 18k gold work, a petit concave kiln-fired enamel plaque mounted in center. I love the griffins at the sides! Definitely bespoke, entirely hand worked by Master artisans, jeweled throughout. Am I completely positive it's not Austrian? I am not, and artists of each were working similarly in early to mid-1800s and even earlier. While the art extends backward by centuries, this one is relatively certainly 1800s. Barrel hinge with 18k gold pin but silver c-clamp and hinge. From an anonymous private collection, England. Full measurements noted on the photos. Very good to excellent condition throughout. Each time I think I've found the tiny French punch mark for silver, it turns out not to be. There is a possibility it is Austrian, as noted. Nothing missing, nothing damaged. I didn't work much at the silver. It is not .950/1000 pure, but likely .800/1000 or perhaps a hair below that standard, which would make sense of not finding the mark.