section_path: Conservation
section_name: Conservation
paragraph_text: Conservation
  
  Sculptures are sensitive to environmental conditions such as temperature, humidity and exposure to light and ultraviolet light. Acid rain can also cause damage to certain building materials and historical monuments. This results when sulfuric acid in the rain chemically reacts with the calcium compounds in the stones (limestone, sandstone, marble and granite) to create gypsum, which then flakes off. Severe air pollution also causes damage to historical monuments.
  
  At any time many contemporary sculptures have usually been on display in public places; theft was not a problem as pieces were instantly recognisable. In the early 21st century the value of metal rose to such an extent that theft of massive bronze sculpture for the value of the metal became a problem; sculpture worth millions being stolen and melted down for the relatively low value of the metal, a tiny fraction of the value of the artwork.