…the traditional definition of a cameo is a piece of jewelry Carved in Relief in stone or shell.
If a cameo is made of lava, it is almost certainly Victorian.
If the cameo is mounted as a brooch, carefully examine the pin and hook. Safety catches are a 20th century adaptation. If the cameo has one, then it is either not older than the early 1900s or a new catch has been added. If it is an addition, this can usually be ascertained by more careful examination. Look for signs of soldering. Often the new catch is attached to a small plate jointed to the back of the brooch. Next look closely at the pin and notice what kind of hinge it has. If the sharp point of the pin extends past the body of the brooch, it is an ‘oldie.’
Gold, silver, pinchbeck, gold filled, cut-steel, and jet were some of the materials used for mounting cameos. Pinchbeck is an alloy of copper and zinc used to create brass that resembles gold. The type of metal used can often give an indication of when it was made. If the mounting is pinchbeck, it was probably made between the early 1700s and the mid-1800s. Gold electroplating was patented in 1840 so, if the piece was plated, it was made after that date. Nine-karat gold was legalized in 1854, and a piece in 9k would have to be made after that date. A popular metal used for mountings in the 1880s was silver, but this does not mean that all cameos mounted in silver were made at that time.
Some materials used to make cameos….
Bog Oak…wood preserved in bogs of Ireland and used to make jewelry during the Victorian era.
Gutta-percha…a hard rubber material made from the sap of a Malayan tree. Discovered in the 1840’s, it was used for making jewelry, statuary, and furniture.
Lava…lava from Mt.Vesuvius, usually carved into cameos or intaglio’s.
Conch shell, Ivory, and stone….
Other materials have been used in the later cameo jewelry…since I don’t deal or collect those pieces I will address them if the need arises.
To test for cracks and to view the transparency of shell cameos, simply hold them to the light.