The look of this pendant reminds me of Austrian and German makers of the (Art Nouveau) period, who did quite a few similar looking pieces, and were adept at enamel work. But there appear to be no markings on the silver frame. It is offered by Earthly Adornments, a fun treasure trove of jewellery, beads and plain fun stuff. They note, “Antique Art Nouveau stunning guilloche enamel scalloped pendant with sterling silver chain. The scalloped round enamel has been newly set in a prong set sterling silver backing. There are a few very tiny nicks to the enamel visible under a loupe, otherwise excellent antique condition. Pendant is 1-3/16 inches in diameter. Vintage sterling 15-1/4 inch chain and clasp.”
It sells for USD$150.