Presentation on theme: "W. Kloppmann (BRGM), V.Vergès-Belmin (LRMH) C. Gosselin (LRMH, CICRP) O. Rolland (restorer) Ph. Bromblet (CICRP), J.-M. Vallet (CICRP), E. Dotsika (DEMOKRITOS)"— Presentation transcript:
W. Kloppmann (BRGM), V.Vergès-Belmin (LRMH) C. Gosselin (LRMH, CICRP) O. Rolland (restorer) Ph. Bromblet (CICRP), J.-M. Vallet (CICRP), E. Dotsika (DEMOKRITOS) Isotope (sulphur, oxygen, boron) tracing of internal or external origin of sulphates involved in the degradation of French stone monuments (BOS project)
> 2 Context SO 2 from air pollution : main known source of sulphates involved in stone degradations (black crust, epigenic gypsum layer, microcracking inside the stone giving rise to scaling, plate formation, contour-scaling…) Frequently observed dramatic cases of stone decay on French Monuments nearby partially dissolved « plaster of Paris ». (plaster from former restorations or, more rarely, used as an original material). example: castle of Azay-le-Rideau (Loire Valley) beginning XX centuryend XX century
> 2 Isotope techniques in environmental studies « Fingerprinting » of sources of pollution Tracing processes that lead to isotopic fractionation (sulphate reduction…) Origin and fate of pollutants Classical isotopic studies on stone degradation using sulphur isotopes in Prague : works of F. Buzek et J. Šrámek Supplementary constraints on hypotheses through combination of several isotopic tools (« toolbox ») use of S and O isotopes of sulphates (intrinsic tracers) and of boron isotopes (co-tracer) in coastal environment (source of salts).
> 2 Context Ongoing project on representative selection of French historical Monuments (project BOS, ): Sulphur, oxygen and boron isotopes as tracers for the origin of sulphate néoformations Co-financed by the French National Research Programme on Sciences and Conservation of the Materials of the Cultural Heritage Isotopic characterisation: 34 S and 18 O of sulphates 11 B of boron in potential pollution endmembers and in altered building stones 5 study sites: Chenonceau castle Chartres Cathedral Versailles castle (statues) Bourges Cathedral Marseille Cathedral
> 3 Sampling
> 3 Sampling Bourges > Samples for isotope analyses 4 black crusts 9 « Roman Cement » type mortars 4 plasters 7 altered building stones
> 3 Results Bourges > Black crusts Very homogeneous isotopic composition ( 34 S near 0 ‰), similar to that of other European towns 34 S < values measured in Dresden (combustion lignite, Klemm & Siedel, 2002) Hypothesis of Klemm & Siedel, 2002: 34 S increases with degree of pollution (dusts?). 18 O 7,1 to 9,9 ‰ > reference Antwerp (Torfs et al., 1997) Reference :Study 34 S Buzek et Šrámek (1985) Šrámek (1988) Prague+1,8 à +4,5 ‰ Torfset al. (1997) Antwerp-8 à -1 ‰ Longinelli et Barteloni (1978)San Marco, Venise+4,6 à +5,6 ‰ black crusts
> 3 Results Bourges > Plasters rather homogeneous 34 S values, more variable 18 O Overlap with Lutetian gypsum of Paris basin (Fontes & Thoulemont, 1987), origin of « Paris plasters » plasters
> 3 Results Bourges > Mortars (« Roman cement ») Two groups with distinct rather well constraint isotope signatures Group 1: High 18 O, negative 34 S (depleted in 34 S). Isotopically light sedimentary sulphur: secondary sulphates from sulphide oxidation in marlstones used for production of “roman mortars” mortars group1 mortars group2 Group 2: 18 O and 34 S in the field of atmospheric sulphates, mostly air pollution derived sulphate overriding sedimentary signature.
> 3 Results Bourges > Decayed building stones isotopic composition between the 3 potential endmembers, PAD6 : partly plaster derived sulphates PAD2, PAD5 : partly mortar derived sulphates? PAD3 depleted in 34 S and 18 O with respect to pollution endmembers -- > contribution of sedimetary sulphur in the building stones (oxydation of pyrite by rain water) ?
> 3 Results Bourges > Case of PAD6 proximity of stone degradation to plaster reparation of a capital (« Saint Ursin portal) contribution (by diffusion) of sulphates of plaster
> 3 Results Chenonceau black crust plaster, mortar > Black crusts: In the same field as Bourges black crusts > Plasters: “Paris plaster” signature comparable to Bourges plasters and to Lutetian gypsum > Mortars: “Paris plaster” signature evaporitic gypsum containing mortars Common pollution endmember with plasters > Deteriorated stone: Bipolar mixing of 2 pollution endmembers: Atmospheric pollution and plaster/mortar derived sulphates. Important use of plaster for 19 th -20 th century restaurations
> 3 Results Chenonceau > Deteriorated stone: Ce-PA4: “pure” plaster signature Plaster reparations in the vicinity (in large quantity below) Dissolution-diffusion processes Ce- PA4 Plaster reparations
> 3 Conclusions > Clear contrasts of isotope signature of the different internal and external pollution endmembers black crusts (external) plasters (internal) mortars (internal) > Rather homogeneous signature within each of the endmembers > Secondary sulphates in decayed stone samples show signatures indicating mixing of internal and external endmembers Chenonceau: Clear influence of plaster/mortar gypsum on stone degradation in the vicinity of the reparations, mainly atmospheric input at the highest parts of the building, intermediate position for other samples bipolar mixing of external and internal sources Bourges: Distinct signatures of plasters and mortars (2 groups), and of black crusts. Deteriorated stones show ternary mixing of the endmembers.