SG-OSL analyses of 35 mortar samples originating from five different monuments will be compared.
The objective is to discuss all the aspects from the sample preparation via specificities of the measurement protocol and data evaluation to the age estimation, thereby underlining the importance of material characterization prior to the SG-OSL analysis.
Three categories of mortars were identified: samples without any exploitable SG-OSL signal, samples that could have been reliably dated and poorly bleached samples affected by microdosimetric variations whose dating still remains complicated.
Finally, the hypothesis on distinguishing between reliable and questionable dating results is raised and the potentials of the method for dating mortars are pointed out.
Three different sampling procedures were employed, depending on the solidity of the mortar: The use of a core drill often represents the only possible way of sampling if the mortar is solid and occurs in very thin layers in standing brick or stone masonry.
However, such an intervention has to be performed under water cooling, which affects the original water content of the sample.
Apart from SG-OSL measurements and annual dose rate determination, the samples are systematically studied by means of optical microscopy, EDX-SEM cartography and beta autoradiography in order to evaluate the possible microdosimetric heterogeneity of each sample, arising principally from local variations of potassium content.
Thanks to relatively recent developments of single grain attachments that are becoming a more and more frequently used tool for OSL analyses in recent years, the problem of age over-estimation arising from partial bleaching can be overcome.
Finally, archaeological doses (paleodoses) are calculated by using central age model (CAM), minimum age model (MAM) and internal-external consistency criterion (IEU).
The appropriateness of these models for the exploitation of the measured SG-OSL data as well as for a hypothesis on the estimation of the input parameter needed to run these models are discussed.
The aim of the preparation procedure for single SG-OSL measurements in this experiment was to extract the quartz grains of the size fraction 200–250 μm that were not exposed to light during sampling, following the hypotheses that the coarser fraction is supposed to be better bleached in the case of mortar (i.e. If the samples are compact, the external part that might have been briefly exposed to light during sampling is scraped off.
In order to do so, the use of manual tools is preferable to using a saw since the latter causes quite important loss of material and there is a risk of sample disintegration during cutting.