A06_12

Grain fractions versus time intervals – mortars radiocarbon dating

Michalska D¹,  Hajdas I²

¹Adam Mickiewicz University, Institute of Geology, Poznań, Poland, ²Laboratory of Ion Beam Physics, Dep. of Earth Sciences, ETHZ, Zurich, Switzerland

Pretreatment is very important issue in case of mortars dating. Depending on the composition of the mortar, various preparation techniques allow to obtain the actual age of mortar production and thus the erection of a given wall (Modis 1 and 2). Due to the methodical nature of the work, selected mortar samples from Royal Castle in Poznań were ¹⁴C measured in different time interval and different grain fractions.

The construction of the castle began in the north-west part of a small hill. Due to the unstable ground, a stone foundation was created in the first stage and poured over with lime mortar. Then the castle walls were built of brick.

Radiocarbon dating of mortars provide the first attempt to determine the age of castle buildings.

In the case of these mortars, the results of the ¹⁴C measurement showed that the most important factor influencing the real age of the castle construction, was the time interval in which the gas portion was collected during the chemical decomposition of carbonates. It was connected with the composition and preservation state of those mortars. Selection of the appropriate time interval in which the gas is collected for measurement, as well as the method of preliminary preparation can be adapted to a specific type of mortars.