Sculpted altarpiece by Francesco Laurana - Cicrp

Deterioration of the altarpiece sculpted by Francesco Laurana for thelargely demolished “Vieille Major” cathedral of MarseilleImpact of earlier restoration campaigns on the saline deterioration of reusedmarbleA little backgroundThe altarpiece sculpted by Francesco Laurana at the end of the fifteenth century for the formercathedral of Marseille (today known as the “Vieille Major”) was one of the first Renaissancemasterpieces to be executed in France. Unfortunately, the white marble in which it wassculpted is disintegrating and peeling. A restoration based on several analyses and involvingin particular the quantitative determination of soluble salts was carried out in 1997–98 withthe aim of halting the deterioration and rescuing this masterpiece. Regrettably, this operationproved unsuccessful and the altarpiece has continued to deteriorate rapidly. As a consequenceof this failure, in-depth documentary and scientific studies were undertaken to draw up aprecise diagnosis of the alterations suffered and propose restoration and conservationprocedures best suited to safeguarding this prestigious work.The altarpiece has a double semicircular arch structure under which is positioned the altardedicated to Saint Lazarus. It consists of a set of sculpted white marble blocks, in all about sixmetres high and five metres wide (Figure 1).Figure 1. Diagram of the altarpiece, showing sampling sites for the quantitative analysis ofsoluble salts (the red arrows indicate the two arch stones taken down forexamination).Commissioned in 1477 by the cathedral chapter, this work is inscribed with the date 1481 andwas sculpted by Francesco Laurana, aided by several other Italian sculptors, includingTommaso Malvito (Rouquette 1974, 435–441). The altarpiece is positioned at the rear of the

north wing of the transept of the former cathedral of Marseille, Notre-Dame de la Major, nowknown as the “Vieille Major”. Building work on this cathedral, located on an esplanadeoverlooking the harbour, began in 1150 and the edifice was partially demolished around 1850to allow for the construction of the new cathedral, Sainte Marie Majeure, known as the“Nouvelle Major”. The earlier cathedral is currently closed to the public and for worship. Itsstate of conservation is less than satisfactory despite several restoration campaigns carried outin the twentieth century.I. Earlier restoration projects focusing on the altarpieceNineteenth-century prints and photographs reveal the existence of missing parts anddeteriorations (Evangélisti, Diaz Pedregal, and Rager 2003) as well as several traces of earlieroperations still visible on the altarpiece: partial filling with grey cement mortar, and to a morelimited extent with gypsum plaster, as well as repairs made to the sculpted relief with a lightgrey mortar covered with a white layer to approximate the colour of the marble.Documentary research in the city archives found often partial records of work presumablyperformed during several earlier operations whose actual execution nevertheless remains opento doubt:- a procedure recommended by Architecte en chef des Monuments historiques(ACMH) J. Formigé in a report filed in 1922 and approved during a meeting of themunicipal council for an overall dusting, filling with cement, reattachment of loosepieces, marble inlays in the missing sections joined to new pieces reproduced fromthe remaining sections;- a quote providing very little details submitted by the sculptor-restorer M. Maimpontedated 17 December 1954, calling for general cleaning, a patina, plastering at the rearand under the arches, the sealing of broken pieces and the elimination of metalbraces;- a quote submitted in 1958 for “careful cleaning using a wool rag and marble wax ofthe Saint Lazarus altar” by a masonry and stone-cutting firm from the region(Vivian), corresponding to a service order of 15 July 1958 signed by the ACMH J.Sonnier.The cathedral’s limestone roofing was redone in 1993–94 by the ACMH J.-P. Dufoix toaddress leaks resulting in major water infiltrations in the masonry.Upon the completion of a preliminary study carried out in 1997, including in particular amapping of the alterations and the presence of soluble salts in various areas of the altarpiece,well-documented restoration work was undertaken by an experienced sculpture restorer whoapplied two processes as follows:- in 1997, the preliminary reinforcement of highly altered sections using ethyl silicate(Wacker OH);- in 1998, the reinforcement of altered sections using Rhodorsil RC 90 (a Rhodiaproduct, consisting of a mixture of ethyl silicate and methylphenylpolysiloxane).Less than a year later, the alterations returned to a dramatic extent, threatening the sculpteddecoration.

An initial examination revealed that the alteration was occurring especially on the sculptedsurfaces (based on the mapping) and that the soluble salt content assumed to be the cause ofthis deterioration was low in the core of the marble (Boule 2001, 20). Measurements using acapacitive probe taken to determine the origin of solutions and soluble salts revealed thatwater content was higher at the top of the altarpiece, in the portion joined to the masonry bysmall brick arches. From these findings, it was thus possible to conclude that the solutionsloaded with soluble salts very likely originated in this humid wall (via the small arches) andhad a high salt content due to the infiltration of rainwater prior to the repair of the roofing.In 2003, the CICRP was asked to review this deterioration and carried out a full diagnosticstudy based on new tests and samplings (Figure 1) as part of a research project onmechanisms for stone deterioration by soluble salts (Désarnaud 2004).II. Study methodologyAfter an observation phase on site, involving the erection of scaffolding to provide access tothe entire sculpted façade, some twenty samples of deteriorated marble and greyish repairplaster were taken at various points throughout the altarpiece. Described with the aid of astereoscopic microscope, a number of different types of analysis were performed on thesesamples:- petrographic examination of polished and thin sections;- examination with an environmental scanning electron microscope (ESEM, in this casea Philips 330 provided by the shared analysis service of the Université de Marseille –Provence Saint Charles) employing energy-dispersive X-ray spectroscopy (EDAX) forthe elemental analysis of samples;- analysis of organic phases using a PerkinElmer Spectrum 2000 spectrometer forFourier transform infrared spectroscopy (FTIR), featuring micro-ATR (microattenuatedtotal reflection) technology, with a germanium crystal to perform contactsurface analyses over areas about 100 µm by 100 µm;- analysis of mineral phases crystallised by X-ray diffraction (using a PANalyticalX’Pert Pro multipurpose X-ray diffractometer together with an X’Celerator detectorand silicon powder in a 100 µm capillary, operating at 40 KV and 55 mA with acopper anode);- quantitative analysis of chloride and sulphate anions using ion chromatography and ofsodium using flame emission spectroscopy on soluble salts after agitating samples in asolution following the Italian NORMAL method, described in document 13/83 of theConsiglio Nazionale delle Ricerche (CNR), dosaggio dei sali solubili (Billault 2004);- examination of the cathodoluminescence (CL) colour under an electron microscopeand calculation of the quantity of light using a photoelectric cell. A second series ofmeasurements was taken using a photomultiplier and a spectrometer connected to ascanning electron microscope (SEM).- Finally, measurements of ultrasonic velocity through the material were taken to assessits internal cohesiveness (using the AU2000 60000 Hz tester made by CEBTP). Thesemeasurements were taken on arch stones of the right lunette that had been removed fordesalination testing.III. Presentation of findings

- Material identificationThe marble used is a fine-grained type, with very few grey veins. Petrographic andcathodoluminescence examinations helped identify the material as Carrara marble (averagegrain of 250 µm, maximum grain size of 500 µm). Sculpted areas were discovered on theback of two of the arch stones removed from one of the altarpiece’s upper lunettes (Figure 2).These sculpted areas suggest that the marble used was recovered from an ancient monument,very likely one found in the vicinity.Figure 2. View of the rear of one of the two arch stones removed from the rightlunette, showing mouldings, very likely from an ancient column.- Description of deteriorationsThe two main types of alterations affecting the sculpted surface of the marble are granulardisintegration and peeling. Granular disintegration corresponds to the loosening of grains ofcalcite from the marble, in the form of a fine sand, giving the piece a pitted, uneven surface,as if it had suffered erosion (Figure 3).

Figure 3. Granular disintegration of the marble on the springer of anarch with partial preservation of the brownish, translucent layer (wax).The surface of the marble is powdery and lacks cohesion. Peeling refers to the formation ofscales in the marble, whose thickness ranges from several millimetres to about one centimetre.In the most seriously affected areas, several scales may overlap each other, reaching severalcentimetres in depth (Figure 4).Figure 4. Overlapping of successive peeling (similar in appearance to onion skin weatheringof rock in natural environments) on the frieze where the dedication to Saint Lazurus isinscribed.These two types of deterioration, often combined, are not seen over the entire surface of thealtarpiece, but are concentrated in its upper portion.

The ultrasonic velocity measured in the two removed arch stones varies between 0 and 1500m/sec, whereas the speed of sound measured in fresh-cut and undamaged marble usually is inthe range of 5 to 6000 m/sec (Simon and Snethlage 1996). These very low readings clearlyindicate that the marble has suffered deterioration and is certainly porous and cracked.- Characterisation of earlier restoration proceduresEvidence of several earlier restoration operations was revealed on the surface ofthe marble.A coating with a thickness of a few dozen micrometres, containing a high percentage offluoride, silicon and magnesium, was noted on the calcite grains closest to the surface (Figure5).Figure 5. Retrodiffused electron image (SEM) of a grain of calcite on the surface of themarble covered with a thin layer of magnesium fluorosilicate (EDS spectrum), polishedsection. A thin layer of protective coating (ethyl silicate and polysiloxane) and a thick layerof surface wax cover the fluorosilicate treatment.This thin (10 to 20 µm) and non-uniform layer, only in evidence on a few grains, very likelycorresponds to the remaining traces of a treatment using magnesium fluorosilicate, aprocedure known and applied in Europe in the nineteenth century to protect stone (Lazzariniand Tabasso 1989).A thick, organic layer (50 to 500 µm), light brown in colour, translucent and pock-markedwith bubbles, covers the entire sculpture. Infrared spectroscopic analyses (using micro-ATRtechnology) enabled the identification of this layer’s composition, whose spectrumcorresponds to that of beeswax (Figure 6).

Figure 6. Infrared spectrum of the light brown layer on the surface of the marble(sample VM5) compared to that of beeswax.In the deteriorated areas, a greyish mortar with high alkaline content (Na, K) had been used torepair sculpted details. Analyses indicate that this mortar consists of lime aggregates with acalcite-based binder, therefore resulting from the carbonation of portlandite in contact withambient air. The presence of several hydrates akin to toberomite (calcium silicate hydrates)indicates that a hydraulic setting had also taken place. Residual anhydrous grains of C3A(celite) and C2S (belite), mineral phases typical of hydraulic binders, were also discovered.The mortar used was therefore very likely of the hydraulic lime type. Repairs carried outusing this hydraulic lime mortar were then covered with a white limewash (30 µm thick)consisting of pure calcite and therefore achieved using a non-hydraulic lime mortar, to ensurethe best adherence to the sculpture.All of these earlier operations bear witness to an ongoing process of deterioration at work formore than a century.Analysis also revealed the two silicon-based treatments applied in 1997 and 1998 for thepreliminary reinforcement and reinforcement of the marble. Among other findings, elementalanalysis and X-ray distribution maps of elements (Si, Ca) indicate good absorption of theproducts used, to a depth of several millimetres (Figure 7).Figure 7. Retrodiffused electron image (SEM) and X-ray distribution maps of siliconand calcium (EDS) on the surface of the waxed marble showing, on the polishedsection, the penetration of silicon-based protective coatings (ethyl silicate andpolysiloxane) in the intergranular porosity of the altered material.

However, this protective coating turned out not to be effective over the long term, whereas thewater-repellent aspect of the products used, demonstrated by spraying microdrops of water onthe surface of the marble (pearling effect), has lasted for ten years.Analysis shows that the deterioration of the marble is clearly due to salt crystallisation. Thesalts involved are halite and gypsum. This type of alteration would be expected for reusedmaterial, very likely obtained from the dismantling of an ancient monument, a materialdoubtlessly more porous and fragile than freshly extracted and intact marble. As the formercathedral is located on the harbour, sea spray and rainwater are very likely responsible for thepresence of soluble salts. Until the cathedral’s roof was repaired in 1993–94, the building wassubject to water infiltration due to the lack of watertightness of the limestone roofing. Theseinfiltrations might have caused the sea salts to migrate through the masonry, thuscontaminating the altarpiece, the upper portion of which is positioned against the interior wallby two brick arch stones, with considerable capillary action due to the presence of limemortar.There are other conceivable sources of salts. For example, a portion of the chlorides andsulphates may have originally been present in the reused marble itself, especially if themonument from which it came (or the location where it was stored before being reused) wasalso situated in the same coastal environment. Furthermore, several materials such as cement,hydraulic lime and plaster, used for repairs and filling, are known to be laden with ions(sodium, sulphates, etc.) contributing to the formation of soluble salts (Arnold and Zehnder1989).Analysis shows that a series of surface treatments were applied, up to the last restoration in1997–98. The earliest treatment involved the use of magnesium fluorosilicate, perhaps appliedin the nineteenth century or in 1922 in the course of the restoration supervised by J. Formigé.This type of treatment seals pores in material and hardens the surface (Bromblet et al. 2002,204). Next was the waxing of the entire sculpted surface with a product similar to beeswax.This wax may have been applied as part of the restoration in 1961, as it is referred to in thedocumentation. This organic material forms a film and is water repellent. Lastly, theprotective coatings applied in 1997–98 are known for their water-resistant properties. It iswell known that these pore-closing, film-forming, water-repellent or water-resistanttreatments tend to diminish the stone’s ability to evaporate moisture and, by trapping thesolutions and the crystallised salts under the treated surface, may have intensified thedeterioration (Miquel et al. 2002). The deterioration affecting the marble of Laurana’saltarpiece thus results from a combination of factors, including inappropriate restorationtreatments, in the absence of a preliminary general diagnostic procedure taking into accountthe work and its environment. The study carried out by the CICRP yielded significant datarelating to the causes of the altarpiece’s deterioration and the successive failures of the earliertreatments. It emphasises the difficulty in reaching an understanding of the role of salts on thebasis of analyses of material as limited in porosity as marble. Based on its study, the CICRPwas also able to recommend the types of restoration procedures that could be presumed to bemore effective.Once the findings of this study were made known, the CRMH launched a conservation projectfor this work under the direction of the senior architect and with the scientific assistance ofthe CICRP. The upper half of the altarpiece was carefully dismantled by a stone-cutting firmworking with the team of restorers. This dismantling amply confirmed that the originalmaterial was reused marble, since several blocks revealed mouldings or other recognisablearchitectural forms (columns, etc.) on their reverse sides. The blocks of deteriorated marblewere first given temporary protection by covering their surfaces with gauze. They were then

desalinated by being placed in successive baths of demineralised water (Figure 8) following aprecise methodology enabling the change in the salt content to be monitored so as to optimisethe number of baths and the length of time for each. As for the less deteriorated lower portion,only slightly contaminated by soluble salts, it was decided that it should not be dismantled.The restorers desalinated this part of the work on the surface, by applying clay poultices to theaccessible areas. This desalination is a long process. This project is still ongoing in 2012. Thefirst blocks to be desalinated have been drying for several months and do not show anyrecurrence of the alterations.Figure 8. Marble arch stone in its desalination bath.For further information…Arnold, A., and K. Zehnder. 1989. Salt weathering on monuments. In Proc. 1 stInternational Symposium on the Conservation of Monuments in the MediterraneanBasin, Bari, ed. F. Zezza, 31–58.Billault, V. 2004. Dosage de sels solubles, église de la vieille Major à Marseille. Reportissued by ERM (Poitiers).Boule A. 2001. Cathédrale de la Vieille Major – chapelle Saint Lazare – retable de FrancescoLaurana – diagnostic de l’altération du retable. Report issued by LERM (Arles).Bromblet P., J. D. Mertz, V. Vergès-Belmin, and L. Leroux. 2002. Consolidation ethydrofugation de la pierre, dossier technique. Monumental : Revue scientifique et techniquedes monuments historiques. Paris: Editions du Patrimoine, Centre des monuments nationaux,200–243.Désarnaud, J. 2004. Etude de la dégradation du marbre du retable de F. Laurana (VieilleMajor, Marseille). Mémoire n° 597, Université Bordeaux 3, DEA Archéomatériaux.Evangélisti, E., P. Diaz Pedregal, and G. Rager. 2003. Préservation du retable de FrancescoLaurana, Chapelle Saint Lazare, cathédrale de la Vieille Major, Marseille, rapport de phase 1.

Lazzarini, L., and M. L. Tabasso. 1989. La restauration de la pierre. Maurecourt: ERG.French translation by J. Philippon.Miquel, A., P. Bromblet, V. Vergès-Belmin, L. Binda, G. Baronio, E. De Witte, H. De Clerq,R. Van Hees, and H. Brocken. 2002. Experimental study on the compatibility of apolysiloxane treatment with substrates loaded with sodium sulphate: influence of the physicalproperties of the substrates on the salt content limit. International Journal for Restoration ofBuildings and Monuments 82, no. 2/3: 271–291.Rouquette, J. M. 1974. Provence romane, tome 1. La nuit des temps 40. La Pierre-quivire:Zodiaque.Simon, S., and R. Snethlage. 1996. Marble weathering in Europe – results of theEurocare-Euromarble exposure programme 1992-1994. In Proc. 8 th InternationalCongress on Deterioration and Conservation of Stone, Berlin, ed. J. Riederer, 159–166.This text is excerpted from the following publication:Bromblet, P., J. Désarnaud, J.-M. Vallet, A. Blanc, and P. Blanc. 2009. La dégradation duretable sculpté par Francesco Laurana pour l’ancienne cathédrale de Marseille (la vieilleMajor) : impact des anciens traitements de restauration dans le processus de dégradation salined’un marbre de réemploi. In Proc. 7 th International Conference of the Association for the Studyof Marble and Other Stones used in Antiquity (ASMOSIA). Aix-en-Provence: Maisonneuve &Larose, Maison méditerranéenne des sciences de l’homme.Project participantsCultural property: classified as a “Monument historique”Time period for the project at the CICRP: This study was carried out by Julie Désarnaudduring her six-month research internship at the CICRP in 2009 in partial fulfilment of therequirements for the second year of her master’s degree.Owner of the cultural property: French stateCICRP: Philippe Bromblet (research scientist), Jean-Marc Vallet (research scientist)Conservator-restorer: Sculptura (team headed by Colette Brussieux)Senior historical architect: François Botton