Hardstones such as agate or sardonyx, shell, and glass were carved three-dimensionally into vessels, plaques, ring-stones, or pendants so as to take advantage of the contrasting colours of different layers of the material. The technique was first employed in the Hellenistic period, and reached its apogee under the Roman empire. The most elaborate surviving cameos are the Tazza Farnese (in Naples), the Gemma Augustea (in Vienna), and the Cameo of *Tiberius (in Paris); they carry complex figured scenes of a mythological and political nature. The cameo was a much favoured vehicle for portraiture; notable examples are the idealized superimposed heads of *Alexander (3) the Great and *Olympias (or of Ptolemies, see ptolemy (1)) on cameos in Vienna and St Petersburg. Large-scale cameos played a part in the circulation of imperial ideology; smaller ones reveal private devotion to a range of deities, carry scenes of everyday life, or bear inscriptions relating to love or health. Hardstone cameos were intrinsically valuable; less expensive items might be made in layered glass. The Portland vase is the most outstanding extant object in this category. See portraiture, greek; portraiture, roman.