Any theoretically chronometric dating technique which uses the thermo-remanent magnetism of certain types of archaeological material. These methods use the known changes have taken place in the direction and intensity of the earth's magnetic field. Magnetic minerals present in clay and rocks each have its own magnetic orientation. When heated to the so-called blocking temperature, the original magnetic orientation of the particles is destroyed, and they will take on the orientation of the earth's magnetic field in a fixed alignment - which does not alter after cooling. These methods are most suitable for kilns and hearths. Once the direction of the archaeological sample has been determined, it may be possible to date it by fitting it to the secular variation curve established for the local area. There is no universal curve, since not only the earth's main field varies, but there are also local disturbances. Since the dating of the curve has to be constructed through independent dating techniques, and these are not available for every area, there are not established curves for every region. As a dating technique, it is strictly limited to those areas where dated curves have been established. A more recent dating technique using thermo-remanent magnetism is palaeointensity dating (archaeomagnetic intensity dating). The principle is that the thermo-remanent magnetism in burnt clay is proportional to the intensity of the magnetic field acting on the clay as it cools down. The measurement of its intensity, and a comparison with the intensity revealed by reheating in today's magnetic field, gives a ratio for the past and present fields which can be used to establish a curve of variation in the earth's magnetic field intensity. The method promises to be useful since direction in situ is not required and it can therefore be used for pottery and other artifacts as well as hearths and kilns.