AMS C-14 DATING OF LIME MORTAR

A method for refining lime mortar samples for C-14 dating has been dev eloped. It includes mechanical and chemical separation of mortar carbo nate with optical control of the purity of the samples. The method has been applied to a large series of AMS datings on lime mortar from thr ee medieval churches on the Aland Islands, Finland, The datings show c onvincing internal consistency and confine the construction time of th e churches to AD 1280-1380 with a most probable date just before AD 13 00, We have also applied the method to the controversial Newport Tower , Rhode Island, USA. Our mortar datings confine the building to coloni al time in the 17th century and thus refute claims of Viking origin of the tower. For the churches, a parallel series of datings of organic (charcoal) inclusions in the mortar show less reliable results than th e mortar samples, which is ascribed to poor association with the const ruction time.