I understand from people who have seen the Marlin film of Colour Case Hardening that it contains a number of factual errors. Such as there being no top on the crucible when it is put into and withdrawn from the furnace. Also the the very close proximity of the operators hand to the supposedly red hot crucible. (already mentioned here). It has been suggested that the film was made to be deliberately misleading in order to foil competitors seeking to emulate Marlins methods and colours.

Harry

Biology is the only science where multiplication can be achieved by division.