1920's Old European Diamond Engagement Ring in Platinum1920s Old European Diamond Engagement Ring in Platinum. This Art Deco engagement ring features beautiful open work on its shoulders and a . 64 carat Old European Cut diamond at the center. The center stone is beautifully surrounded by . 20 carats of accent diamonds in wide domed pattern with neat grooves in the platinum mounting. This ring is gorgeous in its symmetry and neat metalwork.