Item: Antique Georgian Sterling Silver Diamond Paste Buckle Brooch. This not stamped. It's testing as sterling silver. The stones are imitation diamonds made from glass (paste). 
 
Measurements: 1 & 1/2 inches X 1 & 1/4 inches. It weighs 12.28 grams.
 
Condition: Antique, previously owned. There are only minor signs of age/use/patina.