Being an endothermic reaction, heat is applied to initiate and sustain the reaction. This heat requirement may be very high. To keep reaction temperatures low, the processes are operated under pressure. The rotary kiln is typically used in dolomite calcination. In the rotary kiln, the raw material, calcinated dolomite, is mixed with the finely ground reducing agent, ferrosillicone and the catalyst, fluorite. The materials are mixed together and pressed into sphere shaped pellets and the mixed materials are charged into cylindrical nickel chromium steel retorts. A number of retorts are placed in a furnace in sealed paper bags to avoid moisture absorption so that calcined dolomite activity doesn't reduce magnesium yield. The pellets are then placed into a reduction tank and heated to 1200 °C. The inside of the furnace is vacuumed with a 13.3 Pa or higher, to produce magnesium vapour. Magnesium crystals are removed from the condensers, slag is removed as a solid and the retort is recharged. The crude magnesium is refined via flux, and commercial magnesium ingot is produced.