archaeology Archaeology or archeology is the scientific study of human activity through the recovery and analysis of material culture. The archaeological record consists of artifacts, architecture, biofacts or ecofacts, sites, and cultural landsc ...

anthropology Anthropology is the scientific study of humanity, concerned with human behavior, human biology, cultures, societies, and linguistics, in both the present and past, including past human species. Social anthropology studies patterns of be ...

, a pot boiler or cooking stone is a heated stone used to heat water - typically by people who did not have access to pottery or metal vessels.

In Archaeology

The term refers to a stone used to move

heat In thermodynamics, heat is defined as the form of energy crossing the boundary of a thermodynamic system by virtue of a temperature difference across the boundary. A thermodynamic system does not ''contain'' heat. Nevertheless, the term is ...

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 - or a wooden trough. 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. Such stones can be recognized because the repeated exposure to the heat of the fire followed typically by rapid chilling in water leads to great thermal stress on the stone's fabric due to the

thermal expansion Thermal expansion is the tendency of matter to change its shape, area, volume, and density in response to a change in temperature, usually not including phase transitions. Temperature is a monotonic function of the average molecular kin ...

and contraction. This typically leads to partial glazing of the stone's surface and a fine network of cracks on the stone's surface (often described as "

crazing Crazing is the phenomenon that produces a network of fine cracks on the surface of a material, for example in a glaze layer. Crazing frequently precedes fracture in some glassy thermoplastic polymers. As it only takes place under tensile stre ...

"). Eventually the stone shatters. Individual fragments may be re-used until it becomes infeasible to manipulate the stone into and out of the fire, at which point the fragments are discarded and a new pot boiler (or many new ones) are acquired. Often the broken pot boilers are discarded into middens or domestic waste deposits, which on long-established sites can amount to many tonnes of material. Reuse as building material is not impossible, but the typical small size of the fragments hinders this use. Nordamerikaabteilung in Ethnological Museum Berlin 59

Nordamerikaabteilung in Ethnological Museum Berlin 59

Identification

Surface "crazing" is not restricted to pot boilers - hearth stones and the surrounds of fireplaces may also show the same structure. However, since a pot boiler needs to be manipulated into and out of the fire (typically in anthropological observations, using sticks of green wood) at arm's length, they start off weighing up to several kilogrammes, and shrink by fragmentation ; hearth stones and chimney liners are typically larger.

References

Boilers (cookware) Archaeological artifacts {{Tool-stub

In Archaeology

Identification

See also

References