WHEN WE USED our gemstone tester, we discovered that the domed clear cabochon is GLASS, which we would have never suspected. Normally rock crystal is used for this type of reverse-glass painting, better known as "Essex crystal". But in the late 1800s, someone cheaped out on the materials (maybe?) - a silver frame holds the glass, whereas Essex crystal would normally be mounted in gold. The technique is the same, though: painstaking hand-carving and painting. Look at the blush on that tiny apple! The log's bark! When viewed through the lens, the creatures appear three-dimensional.