What Does the Archaeomagnetic Record of Fired Ceramics Reflect?

A complex of archaeomagnetic and rock-magnetic studies is conducted to compare the archaeomagnetic intensity determined by the Thellier–Coe and Wilson methods with the known “true” value of the geomagnetic field during the firing of the ceramic samples manufactured on February 21, 2017 in Myshkin, Yaroslavl region, Russia. The obtained results show two different values of archaeomagnetic intensity corresponding to two temperature intervals. The values obtained in the low-temperature interval (∼150–350°C) are approximately 13 µT lower than the true value, while the values obtained in the interval of ∼350–600°C are fairly close to the “true” ones. The cause of the phenomenon is likely due to the presence of small magnetic grains in the ceramic under study, which are close in size to superparamagnetic ones and are capable of resuming their growth upon heating and reaching the particle sizes in a single-domain state. The results of rock-magnetic studies suggest that thermoremanent magnetization in the studied ceramics is carried by grains of oxidized magnetite, hematite, and possibly ε-Fe2O3.