This is mid-19th century glass set in sterling silver and measures 1 & 5/8 by 1 & 1/4 inches (NBS large). This subject is not surface painted or inlaid as often described. It was painted in glass frit enamel and fired onto the black glass. It won't ever wash or scrape off :) soaking will not harm it. There are no surface scratches either. It's just a gorgeous hunk of Victorian black glass! I have no reason to think it ever was a brooch.