Amethod for dating fired clay, also called archaeomagnetism. In unfired clay, the grains display an arbitrary magnetic orientation. When the clay is heated, thermal agitation causes the magnetism to change. Certain grains are thus magnetized and align themselves parallel to the terrestrial magnetic field. The direction and intensity of the thermo-remanent magnetism are measured in order to date the firing of the clay. To date a potsherd by the direction of its thermo-remanent magnetism, it must have remained in situ since its firing.