Blowing glass requires a long apprenticeship because the blowing must be regular and continuous until the desired shape is obtained. The job therefore requires a strong physical build and a high lung capacity. Blowing is done while keeping the cane in constant rotation. While the master glassblower blows and rotates, the temperature of the crystal is lowered to 1,184°F (640°C). For the production of pieces with relief sculptures, the mass of crystal is slipped into aluminium, bronze, cast iron, or steel moulds. The moulded-pressed technique was patented by René Lalique in 1909.