Mortar OSL and brick TL dating: The case study of the UNESCO world heritage site of Modena

In this study, TL and OSL dating were applied respectively to bricks and mortars taken from a few key structures of the UNESCO World Heritage Site of Modena (northern Italy). The samples came from the Cathedral and the Ghirlandina Tower, built between the end of the XII century and the first half of the XIV century AD. TL dating of bricks showed that we were dealing with the well-known phenomenon of re-use of ancient Roman bricks. However, it was also possible to discover and date quite precisely a previously unknown renovation phase in the Cathedral apse area (XVI century). Regarding the OSL mortar dating, both Multi-Grain and Single Grain techniques were applied on quartz grains, possibly well bleached during mortar preparation. OSL gave good results for one sample from the Cathedral and three from the Ghirlandina Tower. The other gave ages much older than expected, indicating the possible uncompleted bleaching of the quartz grains as the main problem of this dating application. Finally, the application of the Bayesian statistical approach, reducing the error associated with the data, supported a new building chronology, in particular for the Ghirlandina Tower.