The basis of the dating is Thermal Remnant Magnetism (TRM), discussed in the entry on paleomagnetism. At the time of firing, the direction and intensity of the magnetic field of the Earth may be recorded by iron-bearing minerals such as magnetite contained in baked ceramic material. The ceramic material must be locked into position in the earth, such as in a hearth pit or fire-hardened surface. As time passes, the magnetic field direction of the local environment varies from the direction locked into the ceramic material. The change observed between the present and the recorded magnetic fields may be useful in constraining the elapsed time.
Herries, A.I.R., Kovacheva, M., Kostadinova, M., Shaw, J., 2007. Archaeo-directional and -intensity data from burnt structures at the Thracian site of Halka Bunar (Bulgaria): The effect of magnetic mineralogy, temperature and atmosphere of heating in antiquity, Physics of the Earth and Planetary Interiors. 162, 199-216.