The pleated bowls are beautiful handmade art glass from the Murano region. This manufacturer invented the centrifuge machine and technique that spins molten glass into discs that are then manipulated by hand into various organic shapes. During the process, varying colors and finishes are applied to the glass. While still warm, the pieces are put through an annealing process in a tunnel oven to cool slowly so as not to explode. The annealing process can take anywhere from hours to many days depending on the thickness of the glass. Annealing is a process of slowly cooling glass to relieve internal stresses after it is formed. The process may be carried out in a temperature-controlled kiln known as a Lehr. Glass that has not been annealed is liable to crack or shatter when subjected to a relatively small temperature change or mechanical shock. Annealing glass is critical to its durability.