Sculptures can be created through 4 processes: carving, where material is removed using tools such as chisels, hammers, and files; modeling, where material is added using materials such as clay, wax, paper-maiche, or plaster; casting, where the original form is encased in a material such as plaster, metal, or synthetic materials such as plastic or polyester resins, which hardens and is removed from the original form, creating a mold that can be used over and over again; and construction: metal sculptures can be welded from sheet metal or bent from wire, they can also glue together paper, wood, or board and then remove or add additional materials. Some sculptures can also have moving parts such as Alexander Caldwell's (1898-1976) mobiles.
Alexander Caldwell: 
Caldwell's mobiles
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Environmental art or Earthworks emerged in the 1960s. It is often large in scale and constructed on-site, and is usually permanent. Earthworks can be found constructed in nature or in a gallery or museum. An essential part of the process is the collaboration of environmental artists and government agencies to gain approval for the proposed works
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