Marble (toy) conventions. Additionally, many glass artisans produce art marbles for the collectors' market only, with some selling for thousands of dollars. Marbles are made using many techniques. They can be categorized into two general types: hand-made and machine-made. Marbles were originally made by hand. Stone or ivory marbles can be fashioned by grinding. Clay, pottery, ceramic, or porcelain marbles can be made by rolling the material into a ball, and then letting dry, or firing, and then can be left natural, painted, or glazed. Clay marbles, also known as "crock marbles" or "commies" ("common"), are made of slightly porous clay, traditionally
Elgin Marbles Parthenon, which is regarded as one of the world's greatest cultural monuments. International efforts to repatriate the Marbles to Greece were intensified in the 1980s by then Greek Minister of Culture Melina Mercouri, and there are now many organisations actively campaigning for the Marbles' return, several united as part of the International Association for the Reunification of the Parthenon Sculptures. The Greek government itself continues to urge the return of the marbles to Athens so as to be unified with the remaining marbles and for the complete Parthenon frieze sequence to be restored, through diplomatic, political and legal means. In