Sculptures intended to last for decades or centuries must be made of materials that are resistant to weather, vandalism and theft. Large memorial and decorative sculptures are often made of stone, cement or bronze. Stone was traditionally carved by hand, but modern stone carvers often use power tools. Bronze or other molten metals are poured into molds that are created from artists' clay models. Some metals such as steel and aluminum are assembled by riveting or welding methods and are often used for industrial or modern-looking sculptures.
Ephemeral materials are often purposely used to make a statement of passing time with a nod to the elements of nature and natural processes. Sculptures of this type are made with deterioration and decay in mind. Ice, snow and sand sculptures fall into this category.
Andy Goldsworthy is perhaps one of the most well known ephemeral artists of our time. His work is done using only natural materials found in the region where he is working. He has worked with icicles, twigs, leaves, stacked stones and mounded earth.
Sculptures are often specific to a particular site. The site determines the style, material, scale and subject matter of the sculpture. The artist must go to the site, examine the surroundings and question the owner or guardian of the property regarding his intentions. This kind of sculpture is borne out of specific needs and requirements rather than arbitrary artistic expression. A small garden setting will require a different sculpture than a wide concrete entry to a major corporation, and the site-specific work will be a reflection of the setting.
Art may be created as an event or statement for some short-term purpose with the intention of removing the work after a period of days or weeks. The artist may be commissioned to undertake a work for a special celebration or holiday.
In some cases the artwork itself is the event. The artist Christo and his late wife Jeanne-Claude created work on an enormous scale that requires environmental impact studies and teams of engineers. They are committed to removing their art within a two-week period and restoring the surroundings to the original condition.