Hot rocks and magnetic fields - similar thing with pottery?

"In the preparation of a hangi, the stones are heated to very high
temperatures, and the grains of magnetic minerals lose their
magnetisation. As they cool, they become remagnetised by the prevalent
magnetic field. We hope that, by careful measurement of the
magnetisation of a hangi stone, we will be able to retrieve both the
direction and the strength of the magnetic field in which it cooled."

http://www.victoria.ac.nz/home/research/strengths/earth-physical-sciences/hangi-stones-hold-clues-to-earths-past-geomagnetic-field