Ice sculpture is a form of sculpture that uses ice as the raw material. Sculptures from ice can be abstract or realistic and can be functional or purely decorative. Ice sculptures are generally associated with special or extravagant events because of their limited lifetime. The lifetime of a sculpture is determined primarily by the temperature of its environment, thus a sculpture can last from mere minutes to possibly months. There are several ice festivals held around the world, hosting competitions of ice sculpture carving. Raw material Sculpting ice presents a number of difficulties due to the variability and volatility of the material. Ice may be sculpted in a wide range of temperatures and the characteristics of the ice will change according to its temperature as well as the surrounding temperatures. Sculptures are generally carved from blocks of ice and these blocks must be carefully selected to be suitable for the sculptor's purposes and should be free of undesired impurities. Typically, ideal carving ice is made from pure, clean water. However, clear, transparent ice is a result of the freezing process and not necessarily related to the purity of the water. Clouded ice is often the result of finely trapped air molecules that tend to bind to the impurities while naturally freezing. Mechanically clear ice is usually made as the result of controlling the freezing process by the circulation of the water in the freezing chamber. This process hopes to eliminate any trapped air from binding to the impurities in the freezing process. Certain machines and processes allow for slow freezing and the removal of impurities and therefore are able to produce the clear blocks of ice that are favored by ice carvers. However, not all blocks that are carved are clear ice. White ice blocks look like snow and are sometimes carved. Colored ice blocks are produced by adding dyes to the ice and can be carved as well. In some instances, clear ice and colored ice are combined to create a desired effect. There are various sizes of ice blocks that are produced artificially. Naturally made blocks can be cut to almost any size from frozen rivers or from "ice quarries," which are essentially lakes or ponds that have frozen over. Large ice blocks must be moved by heavy machinery and are used for large ice sculpting events or as part of an ice hotel. Techniques The temperature of