Historical building dating: A multidisciplinary study of the Convento de São Francisco (Coimbra, Portugal)

Abstract

Cross-dating of bricks and mortars from historical building, through thermal (TL) and optically stimulated (OSL) luminescence have achieved good accuracy and precision. However this approach is, in many cases, not exhaustive especially for buildings with different construction phases closely temporally spaced to each other. The uncertainties of experimental data added to the reuse of old bricks and/or the presence of mortars applied on restorations represent the main limits to obtain the complete chronology. In the case of the Convento de S. Francisco (Coimbra, Portugal), the dating results were crossed with the stratigraphic study of the building, mineralogical characterization by XRD and colorimetric data of the mortar samples. Thanks to luminescence ages, mineralogical composition and color specification, two phases of construction were identified: the first from the 17 th century and the first half of the 18 th century and the second from the second half of the 18 th century to the first half of the 19 th century. These results were confirmed by mineralogical characterization and colorimetric measurements of mortars that identify two different types of materials in aggregate/binder ratio terms and superficial optical characteristics.

Modeling Light Exposure of Quartz Grains During Mortar Making: Consequences for Optically Stimulated Luminescence Dating

“…We note that this was also the conclusion of the Milan group at the University of Milan Biccocca, department of Material Sciences, that developed SG-OSL dating of mortars at the same time as Bordeaux (Panzeri 2013). By classical procedures, we mean multigrain techniques including the fine grain technique used by some authors for dating buildings in the Mediterranean area, even though some acceptable results were obtained (Gueli et al 2010;Stella et al 2013Stella et al , 2018Moropoulou et al 2018). After an exploratory stage corresponding to a doctoral research (Urbanová 2015), we started systematically applying SG-OSL in order to improve the historical knowledge of some late antique and early medieval monuments and to enter the international group on mortar dating (MODIS) that today brings together specialists of radiocarbon and OSL applied to mortars (Hajdas et al 2017;Hayen et al 2017).…”

The State-of-the-Art of Dating Techniques Applied to Ancient Mortars and Binders: A Review

“…As suggested by Urbanová (2019) and discussed further in this paper, the mortars from the coastal areas of southern Europe currently seem to have more favorable characteristics for luminescence dating, which may be linked to the origin, sedimentary history and processing of the sand aggregates used to prepare mortar. It is thus possible that the mortars studied by Gueli et al (2010) and Stella et al (2013Stella et al ( , 2018 were globally well-bleached and also that a coarser fraction of these samples would provide satisfactory results with the multigrain procedure. On the other hand, the methodology might prove to be problematic for heterogeneously bleached mortars.…”

“…The findings can be complemented by the results from the "multigrain" studies of the well-dated monuments marked by triangles in Figure 5a. If we assume that obtaining a Gaussian distribution with the "multigrain procedure" indicates a good degree of bleaching, the monuments from Southern Europe (yellow triangles, Stella et al 2013Stella et al , 2018Sanchez-Pardo et al 2017) mainly enter this category. On the other hand, strongly asymmetric distributions obtained with the "multigrain procedure" imply partial or poor bleaching.…”

“…Parallel to the studies that use exclusively the "single grain" measurement systems, conventional multigrain analyses still continues to be used for mortar dating (e.g. Sanchez-Pardo et al 2017;Moroupolou et al 2018;Stella et al 2018;Panzeri et al 2019). Some of the recent studies deal in different ways with this situation.…”

“…Instead of individual sand sized grains, the authors attempted to date a fine-grained quartz fraction (4-11 μm) using the classical multigrain procedure. Since then, it has been tested on a total of 15 mortar samples originating from five different monuments in southern Europe, namely Italy (Stella et al 2013), France (Stella et al 2013) and Portugal (Stella et al 2018). The majority of the dating results is in agreement with TL dating of the adjacent bricks, which was systematically applied for a cross-check of the chronological data.…”