Ice sculpting  is a difficult process . First , ice must be carefully selected so that it is suitable for sculpting . Its ideal material is pure , clean water with high clarity  . It should also have the minimum(=least) number of air bubbles. Perfectly clear ice blocks weighing 140 kg and measuring 100 cmx50 cmx25 cm are available from the Clinebell Company in Colorado . Much larger clear blocks are produced in Europe and Canada or harvested from a frozen river in Sweden . These large ice blocks are used for large ice sculpting events and for building ice hotels.     Another difficulty in the process of ice sculpting is time control . The temperature of the environment affects how quickly the piece must be completed to avoid the effects of melting . If the sculpting does not take place in a cold environment , then the sculptor must work quickly to finish his piece . The tools used for sculpting also affect when the task can be finished . Some sculptures can be completed in as little as ten minutes if power tools are used . Ice sculptors also use sharp chisels   that are specifically designed for cutting ice . The best ice chisels are made in Japan , a country that , along with China , has a long tradition of magnificent ice sculptures . Ice sculptures are used as decorations in some cuisines   , especially in Asia . When holding a dinner party , some large restaurants or hotels will use an ice sculpture to decorate the table . For example , in a wedding banquet it is common to see a pair of ice-sculpted swans   that represent the union of the new couple . Why is ice sculpting difficult according to the passage ?
It is hard to control the size and shape of the ice . The right theme for ice sculpting is not easy to find . The proper tools are only available in some countries . It is not easy to find the right kind of ice and work environment .