Dating of mortar and bricks from the Castle of Kastelholm

In connection with the excavation and restauration works at Kastelholm radiocarbon dating of mortar from the walls of the castle has been attempted. Except for a date clearly affected by old carbonate and a few samples of modern age, the calibrated samples date back to the 14th century. Four bricks from different parts of the tower of the castle dated by the thermoluminescence method gave ages between 1490 and 1600 AD. The TL measurements are made on feldspar inclusions extracted from the bricks. The dating results are in agreement with those from the archaeological investigations.