Ceramics of indigenous peoples of the Americas
The clay body is a necessary component of pottery. Clay must be mined and purified in an often laborious process, and certain tribes have ceremonial protocols to gathering clay. Different tribes have different processes for processing clay, which can include drying in the sun, soaking in water for days, and repeatedly running through a screen or sieve. Acoma and other Pueblo pottery traditionally pound dry clay into a powder and then remove impurities by hand, then running the dry powder through a screen, mixing it with a dry temper, and then mixing water to create a plastic paste. In preparing the clay, potters spend hours wedging it to remove air pockets and humidity that could easily cause it to explode during firing. The clay then needs to "cure" over time.
Mining in Cornwall and Devon
During the 20th century various ores were briefly profitable, and mines were reopened, but today none remain. Dolcoath mine (Cornish for "Old Ground"), the 'Queen of Cornish Mines', was 3500 feet (1067 m) deep, and was for many years the deepest mine in the world, not to mention one of the oldest before its closure in 1921. Indeed, the last working tin mine in Europe was South Crofty, near Camborne, until its closure in March 1998. After an attempt was made to reopen it, it was abandoned. There were local media reports in September 2006 that South Crofty was being considered for re-opening as the price of tin had soared, but the site was subject to a Compulsory Purchase Order (October 2006). On the wall outside the gate is some graffiti dating from 1999: