The cooling jar allows you to change out crucibles rapidly and still protect them from deterioration caused by oxidation. Set hot crucibles safely inside the jar and let them cool fully while you continue working. With the lid closed, the heat of the crucible seals the jar, creating a vacuum; and burns off any oxygen that may be present. The ribbed sides of the jar significantly increase surface area, allowing heat to dissipate quickly. Use with the crucible removal tongs (item 710-906).