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W. Kloppmann (BRGM), V.Vergès-Belmin (LRMH) C. Gosselin (LRMH, CICRP) O. Rolland (restorer) Ph. Bromblet (CICRP), J.-M. Vallet (CICRP), E. Dotsika (DEMOKRITOS)

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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:

1 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 > 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

3 > 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).

4 > 2 Context Ongoing project on representative selection of French historical Monuments (project BOS, 2005-2006): 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

5 > 3 Sampling

6 > 3 Sampling Bourges > Samples for isotope analyses 4 black crusts 9 « Roman Cement » type mortars 4 plasters 7 altered building stones

7 > 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

8 > 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

9 > 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.

10 > 3 Results Bourges > Mortars (« Roman cement ») SEM/EDS Fe-sulphides Fe-hydroxides  pyrite oxydation CaSiAlCO FeS

11 > 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) ?

12 > 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

13 > 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

14 > 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

15 > 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.

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