be produced by fusing two separately cast sheets of glass, or by dipping the base glass into a crucible of molten overlay glass during blowing. The most famous example of a cameo from the early period is the Portland Vase. Shell cameos Although occasionally used in Roman cameos, the earliest prevalent use of shell for cameo carving was during the Renaissance, in the 15th and 16th centuries. Before that time, cameos were carved from hardstone. The Renaissance cameos are typically white on a grayish background and were carved from the shell of a mussel or cowry, the latter a tropical mollusk. In the mid 18th century, explorations revealed new shell varieties. Helmet shells (Cassis tuberosa) from the West Indies, and queen conch shells (Eustrombus gigas) from the Bahamas and West Indies, arrived in Europe. This sparked a big increase in the number of cameos that were carved from shells. Conch shells carve very well, but their color fades over time. After 1850 demand for cameos grew, as they became popular souvenirs of the Grand Tour among the middle class. Cameo subjects Classically the designs carved onto cameo stones were either scenes of Greek or Roman mythology or portraits of rulers or important dignitaries. In history, agate portrait cameos were often gifts from royalty to their subjects. These antique cameos, some more than 2000 years old, are either displayed in museums or are in private collections. Notable historic cameos Gemma Augustea Cameo – Roman, after 10 AD. Two-layered onyx. "Tazza Farnese". An ancient Hellenistic bowl made of a very large cameo and purchased by Lorenzo de' Medici during the Italian Renaissance. Cup of the Ptolemies, a large Roman or Hellenistic vessel. Portland Vase, the best known piece of cameo glass. Great Cameo of France – Roman, c. 23 AD. Sardonyx. Gemma Claudia Cameo – Roman, 49 AD. Five-layered onyx. Herophiloska Cameo – Roman, 14 to 37 AD. This portrait of a man with laurel wreath is probably of Emperor Tiberius. The work is signed "Herophilos Dioskourid[ou]" ("Herophilus, son of Dioscorides"). The colour of the glass was intended by the artist to imitate turquoise. "Gonzaga Cameo": Ptolemy II and Arsinoë II. Sardonyx. 3rd century BC. Agrippina the Elder Cameo. Carved in Italy in the period of 37–41 AD. The carving is a three layer agate. Ptolemaic double cameo-Hellenistic, 278–270/269 BC. Eleven-layered onyx. Blacas Cameo: Roman, about 20–50 AD. This head of Augustus