ARCHAEOMAGNETISM

Measures the Earth magnetic fields of past times recorded in Ceramic Building Materials at the moment of their making.

WHAT IS IT FOR

dating

morphology

technology

origin

composition

alteration

APPLICABLE MATERIALS

Ceramic

Ceramic Building Materials (CBM)

Ceramic Building Materials such as bricks, tiles, kilns,etc.

BRIEF DESCRIPTION

The date is obtained by the intersection of the measured TRM data of the sample with the reference curve of the geomagnetic fi eld. If several intervals of dates can be obtained, another independent dating method or the historical or archaeological context can help provide an indication of which interval is the most probable (Blain et al, 2014)

Archaeomagnetism consists in measuring the Earth’s magnetic fi elds at past times recorded in Ceramic Building Materials at the moment of their making. Although the method is geographically restricted since it depends on the existence of a reference curve per region, there is also the possibility in Europe to resort to a geomagnetic model which allows predicting the secular variation in one site (for the last 3 millenia), even if reference data is little in the area. For the geographical regions where the method has been developed and for which reference curves have been well established, AM can be applied from 1500 BC (in France)- 6000 BC (in Bulgaria) until now (Lanos et al., 1999).

Metrics

  • accuracy

  • time

  • cost

Sampling

in situ

invasive

destructive

TIPS

Advantages

  • provides further information on how the bricks/tiles were fired (which position) and if there has been a later fire

Limitations

  • requires a number of samples (from 20 to a one hundred)

HOW DOES IT WORK?

Archaeomagnetism (AM) is based on: 

  • The fact that the Earth acts roughly like a magnet producing a magnetic field,  a vector whose direction and intensity vary throughout time and from one place to another;
  • The property of the iron oxides (such as magnetite) within ceramics of acting like iron filings submitted to the action of a magnet andrecording this field.

The method consists in measuring the intensity, the inclination and the declination of the TRM from a homogeneous group of bricks or tiles and comparing them with the reference secular variation curves of the known EMF direction and intensity for the given geographical area (Lanos, 1990; 1994; Lanos et al., 1999).

Those reference curves, characteristic of a specific area (of a 1000 km radius), have been built from data of the TRM measured on well-dated archaeological local fired structures (such as Roman, medieval kilns, et. al.).

References