The majority of cameos, both those carved in natural materials and those molded in a man made substance, are set so that the back of the cameo is visible, except when set in an item where covering over the back is necessary or desirable: box lids; lockets and fob seals; many rings.  When the back of a cameo set as a brooch or pendant is covered, the question arises of whether something on the back--flatness or a depression; bubbles or the pock marks left by bubbles--is being hidden.  These are telltale signs that might give away the true nature of a piece that is quite convincing as shell, lava or hardstone when seen from the front.  Backs may be covered completely or with more decorative filigree.

This shell cameo of The Three Graces would appear to be the exception that proves the rule.  However, Howard had the ornamental back added so that he could have the cameo engraved when he gave it to Kay as a memento of their visit (perhaps honeymoon?) to Italy in 1947.

If the indistinct lines of the "carving" did not already give it away as a molded piece, one might think the cameo to the right was hardstone with a carnelian base layer.  The covered back and the attachment of the cameo to its setting by means of a small rivet are sufficient to identify this as an artificial piece.

It is not always the case that a cameo gets a setting worthy of it.

The shell cameo of Aurora on the left, a lovely example of the carver's art, is set in a simple brass setting.  The ornate 18k yellow gold setting shown on the right houses a molded glass cameo.

 This lava cameo is competent, no better, and of Ceres, a common subject, but has certainly been given the royal treatment: 14k gold set with diamonds and sapphires, embellished with enamel.