Use water or mild detergent for cleaning and dry the surface thoroughly. Do not use strong alkaline or acid cleaners that could damage the finish and corrode the metal shell. Protect Dewar Contents Materials stored in a liquid nitrogen dewar with a wide mouth are protected by the extremely low temperature of the liquid nitrogen or the gas that issues from the evaporating liquid nitrogen. When all of the liquid nitrogen has evaporated, the temperature inside the unit will rise slowly to ambient. The rate at which the liquid nitrogen will evaporate depends upon the pattern of container use and the age and condition of the container.
Evaporation increases as insulation efficiency deteriorates with age and rough handling.
Opening and closing to insert and remove materials and moving the unit will also increase the evaporation rate. Or important experiments could be delayed, or critical samples spoiled, if one unexpectedly ran out of liquid nitrogen and then could not perform their cryo ultramicrotomy. So it is of the greatest importance to check the liquid nitrogen level constantly in order to anticipate any such kinds of problems that could arise. Condensed moisture or frost on the outer shell of a refrigerator and abnormally rapid evaporation of the liquid nitrogen are indications of vacuum loss. If vacuum loss is evident or suspected, start thinking immediately about the procurement of a replacement dewar.