Used for glass, metal and paper articles in the laboratory, and for powders, fats and oils pharmaceutically. Penetration of hot air is slow, and a fan is necessary to maintain an even temperature in all parts of the load. The process is divided into three periods: (1) heating up period (about 1 hour for an average load); (2) holding period (45 minutes at 160°C, 18 minutes at 170°C, or 714 minutes at 180°C); (3) cooling-down period of up to 2 hours to prevent glass fracture. Thermocouples are used to check new or repaired ovens; thereafter Browne’s tubes (green spot) are adequate for process control.