An 1800‐year archeological experiment in remagnetization

Limestone masonry from monuments dating from 300AD to 1940, remagnetized partly and progressively with age, parallel to the present Earth's magnetic field. The remagnetization was probably due to viscous remanent magnetization (VRM). Néel's theory predicts that natural VRM acquired at low temperature (TA) over a long time (tA, disappears at a higher temperature (TD) in a short period (tD) in the laboratory. I calibrated TD for the postconstruction remagnetization against the ages (tD) of masonry used in well‐dated, historic buildings in Eastern England. Empirically, tA = m.(TD)b relates acquisition age (tAyears) to demagnetization temperature (TD °C). Lincoln limestone remagnetizes more quickly ( m = 1.298 × 10−6 and b = 3.598 over 1800 years) than Speeton Chalk ( m = 4298 × 10−6 and b = 1.973 over 350 years). Magnetite with an effective pseudo‐single domain or small multidomain size carries the remanence.