Vacuum oven

A vacuum oven comprising:

• (a) a furnace chamber provided in a thermally insulated housing;
• (b) a retort which, in operation, is located within the furnace chamber, the retort having an open end and an opposed distal end, the open end having an opening;
• (c) a door moveable between a closed position in which the open end of the retort is closed and an open position in which the retort is accessible, the door having an outer side wherein the outer side of the door is thermally insulated;
• (d) an inner vacuum seal which, when the door is in the closed position, seals around the opening of the open end of the retort whereby an inner perimeter of the inner vacuum seal faces into and is exposed to an interior of the retort and an outer perimeter of the inner vacuum seal faces into and is exposed to an enclosed volume within the furnace chamber that is exterior to the retort;
• and,
• (e) a heating element,
• wherein, in operation at steady state condition, the distal end of the retort is at a first temperature and the open end of the retort is at a second temperature, the second temperature is at least 85% of the first temperature and the first temperature is over 1,000° C. and, wherein the inner vacuum seal comprises a seal material that is thermally stable at a temperature of at least 850° C.