Pot boiler

In an archaeological / anthropological context, the term refers to a stone used to move heat from a fire to a vessel to raise the temperature of water in the vessel, including for cooking. The stone is heated in a fire or in embers. When hot enough, the stone is transferred into a vessel of water to heat the contents. The vessel may be metal (though this is uncommon, metal normally being tough enough to take direct heat from a fire) or pottery which is not of good enough quality to be directly exposed to the heat of the fire. In a pre-pottery context, the heating can be done by lining a pit with leather, leaves or clay, and then putting in the water followed by pot boilers directly into the vessel.