VTG ruby & pearl sterling plique a jour brooch

Vintage art nouveau style plique-à-jour sterling silver brooch with ruby, pearl, and 3 little marcasites. Gorgeous and unique as-is, this would also be awesome converted into a pendant. Plique-à-jour is a type of enamelling similar to cloissoné, but with no backing so light can shine through. Stamped 925 for sterling silver on back. Maker unknown. Measures 1.75" x 1.5". Pin moves a little stiffly but is secure and structurally sound. No other flaws aside from normal wear that you can see in the photos. Comes from smoke-free fragrance-free home. Questions and offers welcome.