Dorotea Fontana

Historical mortars dating from OSL signals of fine grain fraction enriched in quartz

In the last years the mortar dating through Optically Stimulated Luminescence (OSL) techniques has become a viable support for chronological estimations (date of construction or restoration episodes) of historical buildings. However, the dating of mortar has still open issues mainly regarding the assessment of the bleaching degree of quartz, the analysis of the OSL processes for this type of samples and the need to do appropriate tests for the most correct evaluation of the equivalent dose. This paper discusses the results obtained by OSL dating (blue diode stimulation) on the polymineral fine grain phase, enriched in quartz, extracted from lime mortar samples collected from different sites. Thermal transfer effects, through the behaviour of Equivalent Dose (ED) and recovery tests, degree and time of bleaching were studied. For each mortar sample the adjacent brick was collected; in some cases, sampling of the bricks bracketing a mortar layer was a possibility, thus obtaining a direct comparison with the standard thermoluminescence (TL) dating on the bricks.The results obtained show, for this set of samples, the possibility of dating the mortars through the use of the fine grain fraction provided of a suitable chemical-physical preparation procedure and the verification of the bleaching conditions.

Different approaches to date bricks from historical buildings

The application of Thermally (TL) and Optically (OSL) Stimulated Luminescence on bricks used as building material has allowed solving an chronological issue in the field of historical building dating.The possibility to use one or more methodologies of dating is closely related to the luminescent and granulometric characteristics of the sample. Using some brick samples collected in the church of Sain Seurin in Bordeaux (France), this paper discusses the implications and the possibility to use different approaches and techniques for dating. With this aim luminescence measurements were performed on both polymineral fine grain and quartz inclusion phases extracted from each brick. For Equivalent Dose (ED) and consequently age determination, TL on mixed fine grain fraction (FG), OSL on quartz inclusions (QI) and on mixed fine grain (FG*) fraction, were used. The results obtained suggest the advantage of using OSL technique on fine grain fraction cleaned up by IR stimulation (FG*), but the use of quartz inclusion represents indeed a good alternative.

Characterization of foxing stains in early twentieth century photographic and paper materials

Abstract The subject of this present work is a group of nine historical pictures shot in Palermo by the Sicilian photographer E. Interguglielmi in 1912. They are nine matte-collodion prints mounted on the original cardboard supports and all of them show foxing stains affecting the paper surface. In order to characterise the chemical composition of the supports and investigate foxing spots, non-destructive and micro-destructive analysis were carried out. X-rays fluorescence (XRF) analysis was used to characterise the elemental composition of all the mounting boards, allowing a comparison between the foxing spots and non-affected areas. Laser-Induced Breakdown Spectroscopy was used to investigate the presence of lower atomic number elements, not detectable by XRF, while SEM imaging allowed the investigation of surface appearance and nature of original paper samples from the cardboards.

LIBS and XRF analysis for a stratigraphic study of pictorial multilayer surfaces

The study of painting materials is a primary goal for the historical and artistic characterization of works of artbecause it provides useful information about the original materials and their degradation products, the paintingstechnique and any conservation treatments. However, the archaeometric investigations are very complex because theneed to safeguard the Cultural Heritage makes necessary the use of non or micro invasive techniques. Among thepossible analytical approaches, Laser-Induced Breakdown Spectroscopy, supported by X-ray Fluorescencespectroscopy for a faster elements identification, allows stratigraphic analysis with high spatial resolution enough todiscriminate different layers. Moreover, an integrated approach based on XRF and LIBS investigation is particularlyuseful for the complementarities of the outcomes in terms, both of investigated thicknesses and detectable elementalcontent.This paper aims to validate, in the archaeometry field, the use of LIBS for stratigraphic investigation of paintedsurfaces/objects by means of analytical results obtained from original fragments of mural paintings originating fromdifferent sites and artistic eras. Indeed the focus of this work is to determine the optimum parameters for bothtechniques in order to acquire the maximum information with the least damage to the works of art.The results have demonstrated the usefulness of the LIBS investigation, through that it has been possible toreveal chemical elements undetectable by XRF and to analyse the stratigraphic sequence of paint layers from thesurface up to the support layer. Furthermore they have provided good insight into the different painting layers byconfirming the potential of the LIBS to carried out stratigraphic analyses in a micro destructive way.