Stone sculpture can usually be thought of as any piece of stone which is carved or cut in three dimensions to form an artwork. The variety of carving techniques depends on the range of stones from which sculptures can be created. Granite, limestone, marble and sandstone are the common stones that artists work with. But each of these materials varies substantially in appearance, behavior and nature.
A. Environmental Decay
Environmental decay is frequently found on the exterior surfaces of stone sculptures. It is the result of harsh weather condition, pollutants, erosion, the crystallization of salts on the sculpture surface, and repeated wetting and drying. As the decay is not easily controlled and difficult to reverse, it should be prevented through regular checks and observation.
B. Mechanical Decay
Stones of lower quality and changes in other materials used along with the stone or in its installation results into mechanical decay.
C. Applied Decay
Damage may be caused due to vandalism, inappropriate installation, poor transportation and repair. The surface of most of the outdoor stone sculptures is covered with dirt and dust. Sheltered undersides of the carved stones suffer from the accumulation of a black crust. It is usually stable and sometimes functions as a protective layer despite the fact that this may lead to decay. It is not necessary to clean the surface of carved stones regularly, for the action of cleaning can lead to faster deterioration and distortion, particularly to sandstones, by opening the pores of the stones. The repeated handling and touching of stone sculptures can also lead to the formation of stains from the oils and moisture present in skin. Cleaning should be carried out by a skilled professional conservator using gentle means such as bristle brushes and water only if it is absolutely necessary. Chemicals and detergents should not be used at all costs.