display or as offerings. Jade or other types of greenstone were used in China, Olmec Mexico, and Neolithic Europe, and in early Mesopotamia large pottery shapes were produced in stone. Bronze was used in Europe and China for large axes and blades, like the Oxborough Dirk. Materials and techniques The materials used in sculpture are diverse, changing throughout history. The classic materials, with outstanding durability, are metal, especially bronze, stone and pottery, with wood, bone and antler less durable but cheaper options. Precious materials such as gold, silver, jade, and ivory are often used for small luxury works, and sometimes in larger ones, as in chryselephantine statues. More common and less expensive materials were used for sculpture for wider consumption, including hardwoods (such as oak, box/boxwood, and lime/linden); terracotta and other ceramics, wax (a very common material for models for casting, and receiving the impressions of cylinder seals and engraved gems), and cast metals such as pewter and zinc (spelter). But a vast number of other materials have been used as part of sculptures, in ethnographic and ancient works as much as modern ones. Sculptures are often painted, but commonly lose their paint to time, or restorers. Many different painting techniques have been used in making sculpture, including tempera, oil painting, gilding, house paint, aerosol, enamel and sandblasting. Many sculptors seek new ways and materials to make art. One of Pablo Picasso's most famous sculptures included bicycle parts. Alexander Calder and other modernists made spectacular use of painted steel. Since the 1960s, acrylics and other plastics have been used as well. Andy Goldsworthy makes his unusually ephemeral sculptures from almost entirely natural materials in natural settings. Some sculpture, such as ice sculpture, sand sculpture, and gas sculpture, is deliberately short-lived. Recent sculptors have used stained glass, tools, machine parts, hardware and consumer packaging to fashion their works. Sculptors sometimes use found objects, and Chinese scholar's rocks have been appreciated for many centuries. Stone Stone sculpture is an ancient activity where pieces of rough natural stone are shaped by the controlled removal of stone. Owing to the permanence of the material, evidence can be found that even the earliest societies indulged in some form of stone work, though not all areas of the world have such abundance of good stone for carving as Egypt, Greece, India and most of Europe. Petroglyphs (also called rock engravings) are perhaps the earliest form: images