The annealing arch is used at the end of the hot working process to slowly cool the crystal pieces and thus avoid tension in the material. In this type of furnace – also called an annealing tunnel – the temperature is gradually lowered from 806°F (430°C) to room temperature. Depending on the size and volume of the objects, the annealing process can last from a few hours to several days. Great care is required when handling and introducing the pieces into the arch. After leaving the annealing chamber, the piece undergoes a quality control, the first in a long series, to determine whether it can continue its course.