The measurements of these stones re: 15x4mm navette/ marquis shape shape
The materials are: Doublet set Black Diamond colored glass with C Quality gold foil on the back of each stone. To get the best use of these stones and to increase stone clarity, I would recommend removing the foil in a gentle white vinegar and sea salt solution. These stones can also be set in a closed back setting to hide any foil imperfections.
These stones are Antique and were made sometime in the 1940's in Western Germany