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• SO2 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 century end XX century

> 2 > 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 > 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: 34S and 18O of sulphates 11B 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

Fontes & Thoulem ont (1987) Lute tian gypsum of the P arisBasinm odern

S eaw aterG

ypsu

m c

rust

s on

bu

ildin

gs in

Ant

wer

p (

NL)

To

rfs

et a

l. (1

997)

plaster

m ortar group1

black crusts

4 8 12 16 20 24

18O (SO 4) [% 0 vs. SM OW]

-30

-20

-10

0

10

20

30

34S

(S

O4)

[%0 v

s.

CD

T]

B-PA1

B-PA2

B-PA3

B-PA4

B-PA5

B-PA6

B-PA7

Bourges C athedraldeteriora ted stone

black crusts

plasters

m ortars

pyrite oxida tion?

m ortar group 2

18O

atm

osph

eric

oxy

gen

> 3

Results Bourges > Black crusts• Very homogeneous isotopic

composition (34S near 0 ‰), similar to that of other European towns

• 34S < values measured in Dresden (combustion lignite, Klemm & Siedel, 2002)

• Hypothesis of Klemm & Siedel, 2002: 34S increases with degree of pollution (dusts?).

• 18O 7,1 to 9,9 ‰ > reference Antwerp (Torfs et al., 1997)

Reference : Study 34S

Buzek et Šrámek (1985)

Šrámek (1988)

Prague +1,8 à +4,5 ‰

Torfs et al. (1997) Antwerp -8 à -1 ‰

Longinelli et Barteloni (1978) San Marco, Venise +4,6 à +5,6 ‰

black crusts

Fontes & Thoulem ont (1987) Lute tian gypsum of the P arisBasinm odern

S eaw aterG

ypsu

m c

rust

s on

bu

ildin

gs in

Ant

wer

p (

NL)

To

rfs

et a

l. (1

997)

plaster

m ortar group1

black crusts

4 8 12 16 20 24

18O (SO 4) [% 0 vs. SM OW]

-30

-20

-10

0

10

20

30

34S

(S

O4)

[%0 v

s.

CD

T]

B-PA1

B-PA2

B-PA3

B-PA4

B-PA5

B-PA6

B-PA7

Bourges C athedraldeteriora ted stone

black crusts

plasters

m ortars

pyrite oxida tion?

m ortar group 2

18O

atm

osph

eric

oxy

gen

> 3

Results Bourges

> Plasters• rather homogeneous

34S values, more variable 18O

• Overlap with Lutetian gypsum of Paris basin (Fontes & Thoulemont, 1987), origin of « Paris plasters »

plasters

Fontes & Thoulem ont (1987) Lute tian gypsum of the P arisBasinm odern

S eaw aterG

ypsu

m c

rust

s on

bu

ildin

gs in

Ant

wer

p (

NL)

To

rfs

et a

l. (1

997)

plaster

m ortar group1

black crusts

4 8 12 16 20 24

18O (SO 4) [% 0 vs. SM OW]

-30

-20

-10

0

10

20

30

34S

(S

O4)

[%0 v

s.

CD

T]

B-PA1

B-PA2

B-PA3

B-PA4

B-PA5

B-PA6

B-PA7

Bourges C athedraldeteriora ted stone

black crusts

plasters

m ortars

pyrite oxida tion?

m ortar group 2

18O

atm

osph

eric

oxy

gen

> 3

Results Bourges

> Mortars (« Roman cement »)• Two groups with distinct rather

well constraint isotope signatures

• Group 1: High 18O, negative 34S (depleted in 34S). Isotopically light sedimentary sulphur: secondary sulphates from sulphide oxidation in marlstones used for production of “roman mortars”

mortarsgroup1

mortarsgroup2

• Group 2: 18O and 34S in the field of atmospheric sulphates, mostly air pollution derived sulphate overriding sedimentary signature.

> 3

Results Bourges

> Mortars (« Roman cement »)SEM/EDS

• Fe-sulphides

• Fe-hydroxides

• pyrite oxydation

Ca Si Al C O

Fe S

> 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 34S and 18O with respect to pollution endmembers --> contribution of sedimetary sulphur in the building stones (oxydation of pyrite by rain water) ?

Fontes & Thoulem ont (1987) Lute tian gypsum of the P arisBasinm odern

S eaw aterG

ypsu

m c

rust

s on

bu

ildin

gs in

Ant

wer

p (

NL)

To

rfs

et a

l. (1

997)

plaster

m ortar group1

black crusts

4 8 12 16 20 24

18O (SO 4) [% 0 vs. SM OW]

-30

-20

-10

0

10

20

30

34S

(S

O4)

[%0 v

s.

CD

T]

B-PA1

B-PA2

B-PA3

B-PA4

B-PA5

B-PA6

B-PA7

Bourges C athedraldeteriora ted stone

black crusts

plasters

m ortars

pyrite oxida tion?

m ortar group 2

18O

atm

osph

eric

oxy

gen

> 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

Fontes & Thoulem ont (1987) Lute tian gypsum of the P arisBasinm odern

S eaw ater

black crustsBourges

4 8 12 16 20 24

18O (SO 4) [% 0 vs. SM OW]

-30

-20

-10

0

10

20

30

34S

(S

O4)

[%0 v

s.

CD

T]

C e-PA1

Ce-PA2

C e-PA3

Ce-PA4

C e-PA6

C e-PA7

Ce-PA8

C henonceau C astledeteriora ted stone

black crusts

plasters

m ortars

plaster+ m ortar

Gyp

sum

cru

sts

on

build

ings

in A

ntw

erp

(N

L)T

orf

s e

t al.

(199

7)

18O

atm

osph

eric

oxy

gen

> 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 19th-20th 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.