Rehydroxylation dating
Encyclopedia
Rehydroxylation [RHX] dating is a developing technology for dating fired clay ceramics. It is based on the principle that after a ceramic is removed from the kiln, it immediately begins to recombine chemically with moisture from the environment and thus increases in weight. This weight increase provides an accurate measure of the extent of rehydroxylation [RHX]. The dating clock is provided by the fact that the RHX process follows a precise kinetic law: the weight gain increases as the fourth root of the time which has elapsed since firing. The RHX method and the power law were first discovered by scientists from the University of Manchester
and the University of Edinburgh
.
. Once removed from the furnace, the sample is monitored to determine the precise rate at which it combines with atmospheric moisture. Once that RHX rate is determined, it is possible to calculate exactly how long ago it was removed from the kiln. If the date of firing of a certain ceramic were known from another source, the method could be used inversely to determine the average temperature of the object's environment since firing.
, bone china
and porcelain
.
The rate of absorption of water is affected by the ambient temperature. Thus, when calculating dates, scientists must be able to estimate the temperature history of the sample. This is generally based on temperature data for the location, with adjustments for burial depth and long-term temperature variation from historical records. In addition, any event involving extreme heat may reset the "clock" by drying the piece out completely, as though it were just out of the kiln. For example, a medieval brick that was tested by researchers continued to return a result of 66 years. They finally realized that the brick had been dehydrated by the intense heat of incendiary bombing
and fires during World War II
.
University of Manchester
The University of Manchester is a public research university located in Manchester, United Kingdom. It is a "red brick" university and a member of the Russell Group of research-intensive British universities and the N8 Group...
and the University of Edinburgh
University of Edinburgh
The University of Edinburgh, founded in 1583, is a public research university located in Edinburgh, the capital of Scotland, and a UNESCO World Heritage Site. The university is deeply embedded in the fabric of the city, with many of the buildings in the historic Old Town belonging to the university...
.
Process
A small piece of the ceramic is first removed, weighed, and heated to 500 degrees Celsius, effectively dehydrating it completely. The amount of water lost in the dehydration process (and thus the amount of water gained since the ceramic was created) is measured with a microbalanceMicrobalance
A microbalance is an instrument capable of making precise measurements of weight of objects of relatively small mass: of the order of a million parts of a gram. In comparison, a standard analytical balance is 100 times less sensitive; i.e. it is limited in precision to 0.1 milligrams...
. Once removed from the furnace, the sample is monitored to determine the precise rate at which it combines with atmospheric moisture. Once that RHX rate is determined, it is possible to calculate exactly how long ago it was removed from the kiln. If the date of firing of a certain ceramic were known from another source, the method could be used inversely to determine the average temperature of the object's environment since firing.
Research
The RHX technique was the product of a three-year study by a collaboration of University of Manchester and University of Edinburgh researchers. Though it has only been established on ceramics of up to 2,000 years of age, research is continuing to determine whether RHX can be accurately used on ceramics of up to 10,000 years of age. Research is also underway on earthenwareEarthenware
Earthenware is a common ceramic material, which is used extensively for pottery tableware and decorative objects.-Types of earthenware:Although body formulations vary between countries and even between individual makers, a generic composition is 25% ball clay, 28% kaolin, 32% quartz, and 15%...
, bone china
Bone china
Bone china is a type of soft-paste porcelain that is composed of bone ash, feldspathic material and kaolin. It has been defined as ware with a translucent body containing a minimum of 30% of phosphate derived from animal bone and calculated calcium phosphate...
and porcelain
Porcelain
Porcelain is a ceramic material made by heating raw materials, generally including clay in the form of kaolin, in a kiln to temperatures between and...
.
Technical issues
The RHX rate is largely insensitive to the ambient humidity as the RHX reaction occurs extremely slowly and only minute amounts of water are required to feed it.The rate of absorption of water is affected by the ambient temperature. Thus, when calculating dates, scientists must be able to estimate the temperature history of the sample. This is generally based on temperature data for the location, with adjustments for burial depth and long-term temperature variation from historical records. In addition, any event involving extreme heat may reset the "clock" by drying the piece out completely, as though it were just out of the kiln. For example, a medieval brick that was tested by researchers continued to return a result of 66 years. They finally realized that the brick had been dehydrated by the intense heat of incendiary bombing
Incendiary device
Incendiary weapons, incendiary devices or incendiary bombs are bombs designed to start fires or destroy sensitive equipment using materials such as napalm, thermite, chlorine trifluoride, or white phosphorus....
and fires during World War II
World War II
World War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...
.