Art Deco Aquamarine Engagement Ring in Platinum.  This Art Deco engagement ring features a lovely round cut aquamarine set in platinum. The aqua provides a splash of color to this classic Art Deco design. Set with fishtail prongs inside two small diamond accents, this gorgeous mounting also contains very fine milgrain detail on their sharp square borders. This will make a perfect engagement ring for someone looking for something a little different but still retaining that classic Deco style.