Historical building dating: refinement of established sample preparation protocol

Abstract: The application of thermal (TL) and optical (OSL) stimulated luminescence on pottery and building materials has allowed to resolve numer-ous problems in both the fields of retrospective do-simetry and dating. Routine measurements request the registration of TL signals obtained on polymineral fine-grained frac-tion (FG) extracted from pottery sherds and bricks used as building material with the Added Dose (AD) technique. One of the reasons of the dispersion of the lumi-nescence measurements when using this fraction is the variability of relative contents of quartz and feld-spars, which due to their differing behaviour influ-encing the equivalent dose (ED) and therefore its uncertainties. The objective of the present work is the solution of this type of problem using the double Single Ali-quot Regeneration (d-SAR) protocol which is widely used to date geological sediments. This allows the ED determination from the quartz-dominated OSL signals obtained from polymineral fraction. Materials and methods: Using bricks taken from a building which is the objet of a specific dating pro-gram, we measured some samples prepared and measured with different techniques in order to deter-mine which technique allows as to obtain date with minimum dispersion. The samples were prepared with FG (4-11 micron) technique and measured with standard AD to obtain TL signals and with d-SAR to register OSL signals. This last methodology requested some adaptation because samples from building materials have low signals and therefore natural doses. The data obtained was compared with those re-corded using OSL emissions of quartz extracted us-ing inclusion technique, QI, (90-150 micron), measured with “classical” SAR protocol. Results: The results from different fractions ex-tracted from bricks using specially adapted FG-OSL-d-SAR methodology, where compared with those obtained by FG-TL-AD and QI-OSL-SAR standard protocols. This comparison showed the prospective for the new approach especially in the chronological determination of historical buildings

Interconfronto di datazione TL ed OSL su terracotta

Nell'ambito di uno specifico programma di datazione tramite luminescenza stimolata termicamente (TL) e otticamente (OSL) campioni di terracotta sono stati preparati e misurati con diverse tecniche allo scopo di minimizzare l'errore sull'età ottenuta. I valori di dose equivalente sono stati ottenuti, su aliquote preparate utilizzando il protocollo standard fine grain (4-11 micron), con la tecnica della doppia Single Aliquot Regeneration AR (d-SAR) nel caso dei segnali OSL. I risultati ottenuti verranno confrontati con le età OSL ottenute di quarzo di granulometria maggiore (90-150 micron)

Datazione di malte storiche tramite OSL

L'applicazione della termoluminescenza (TL) alla terracotta, utilizzata come materiale da costruzione negli edifici storici, permette di risalire all'epoca di manifattura della stessa. Questo istante potrebbe, però, non coincidere con la data della fabbrica. Assume, a tal fine, un'importanza fondamentale la possibilità di datare le malte prelevate dalla struttura in esame la cui posa è, infatti, coincidente con l'edificazione. In questa occazione viene presentato il protocollo di misura messo a punto per la preparazione fisico-chimica dei campioni di malta da sottoporre a misure di datazione mediante Luminescenza Otticamente Stimolata (OSL) attraverso la presentazione dei risultati ottenuti su alcuni casi-studio

Historical buildings: luminescence dating of fine grains from bricks and mortar

In the framework of a research program aimed to define the chronology of the structures of the architectonic complex of San Francesco alla Collina (Paternò, Italy), two luminescence dating techniques were applied: Thermoluminescence (TL) on terracotta bricks and Optically Stimulated Luminescence (OSL) on mortars. Dating a historic building through the age of its bricks can be sometimes complex, for the possible gap between the age of the bricks themselves and that of the structure. Considering that the laying of mortar is contemporary to the construction, the principal objective of the work here presented is the verification of the possibility of solving chronological uncertainties of specific parts of a building using simultaneously TL on bricks and OSL on the associated mortar. The dating of bricks was obtained using the polymineral 4-11 m granulometric fraction following the fine-grain technique. Starting from the same granulometric fraction, a new protocol consisting of different etching treatments, associated with a feldspar contamination test, was developed to obtain pure quartz grains from mortar. The study shows the possibility of dating the mortar by luminescence, in particular using the OSL emissions of the fine-grained quartz fraction. The main focus is to provide a procedure where each step was opportunely adapted to mortar, starting from the chemical-physical preparation to the luminescence measurements protocols. The good agreement of OSL dating of mortars and TL dating of associated bricks and the correspondence of these ages with the well documented historical phases, unique at this time, represents an important goal for application. It is possible to assert that luminescence techniques permit the resolution of dating problems regarding historical buildings above all in terms of dating back to the use of the bricks in the construction from the laying of mortars

Historical mortar: luminescence from fine grain quartz

Within the framework of a research programme aimed at the chronological reconstruction of the structures belonging to the architectonic complex of San Francesco alla Collina of Paternò (Catania, Italy), a procedure was carried out using thermoluminescence (TL) and optically stimulated luminescence (OSL) dating, respectively on terracotta bricks and mortar from the same sampling points. The primary methodological aim was to extend the application of luminescence dating techniques to mortar from historical buildings. Because the TL dating method dates the last firing of bricks, it offers a terminus post quem: the results give the period in which they were manufactured. The possibility that these bricks could have been reused complicates the interpretation of data. Contextual historical mortar and terracotta bricks dating could resolve this problem giving a more reliable date for the construction. We report here the results obtained on bricks, undergone the standard fine grain technique, and on mortar, whose chemical-physical preparation required some modifications to this protocol verifying the results step by step. A methodology was thus established to allow, by IRSL (InfraRed Stimulated Luminescence) measurements, the verification of the feldspar component reduction and the acquisition of an enriched quartz phase that underwent OSL dating. The comparison of TL and OSL ages showed a good agreement thus supporting, in this case, the potential of the methodology for mortar datin