The most recognizable and most popular form of sculpture has been created with hard materials. This is also the oldest form of sculpture. Statues, kinetic sculptures and environmental sculpture are all examples of sculptures that use hard materials as a medium. Some materials used are concrete, marble, bronze, clay, limestone, granite, wood, glass, steel and ceramics. Some of the alternative mediums used by contemporary artists are ice, sand and found objects. These sculptures may often be representational (Michelangelo's David), but may create abstract forms as well (Cloud Gate).
Some experimental artists create sound sculptures, meaning the three-dimensional structures also produce sounds. This art may also be known as a sound installation, because the sculptures are regularly installed in art galleries. Some famous artists who are known for their sound sculptures are Alexander Calder, Hugh Davies and Nigel Helyer. Sound sculptures differ from musical instruments in that they are not manipulated by a human player to make sound; they simply make sound on their own due to their design. This medium that makes this type of sculpture unique is the element of sound.
Light sculptures are a unique type of medium because they use various form of light or lighting to create an aesthetic effect. The medium of light may use fractal manipulations or gaseous forms of light (electricity) to produce an image. Some light sculptures produce light due to the hard materials in a sculpture, while others are nothing but light. The most famous light sculptors are Olafur Eliasson and Dan Flavin (the creator of light sculptures made via fluorescent lights).