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Conservation and restoration of two wall painting fragments by Bernardino Luini

An intervention about frescoes torn and transferred on wooden boards and conserved in the Pinacoteca di Brera (Milan)
Giulia Gregori

Résumés

L'étude concerne l'analyse de la technique utilisée par l'artiste et des phénomènes de dégradation, dans le but de freiner les graves problèmes causés par l'utilisation de panneaux de bois pour la conservation de l’œuvre. Grâce à l'analyse technique de cette méthode et à la réalisation d'une campagne diagnostique multispectrale et scientifique sur deux fragments, de nouveaux systèmes de confinement structurelsont proposés, ainsi que de nouveaux protocoles pour restaurer les fragments du cycle de fresques conservés à la Pinacothèque de Brera.

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Texte intégral

I would like to express my warm thanks to all those who have contributed to the realization of this work: Dott. ssa Michela Cardinali, Director of the Cultural Heritage Conservation and Restoration Centre “La Venaria Reale”, Director of the conservation laboratory of the Cultural Heritage Conservation and Restoration Centre “La Venaria Reale” and supervisor of the thesis, Professor Annamaria Giovagnoli for scientific advice and Dott.ssa Maria Beatrice Failla, advisor for the part related to history of art. My special thanks go to Dott.ssa Cristina Quattrini, officer of the Soprintendenza di Brera di Milano, for having given me the permission to study these artworks and start with their conservation. Special appreciation to the assistant supervisors, Dott. Paolo Scarpitti and Dott.ssa Emanuela Ozino Caligaris, as well as to the professors and conservators of the Istituto Superiore per la Conservazione e il Restauro in Rome. I would like to give special thanks to Mrs. Pinin Brambilla Barcilon for having authorized me to study the documents from her personal archive in Milan and also to Dott.ssa. Sara Abram, whose help was crucial for organizing this first crucial meeting. Finally, I would like to thank the Staff of the Scientific Laboratory and of the Imaging Laboratory of the Centre for Conservation and Restoration of Cultural Property “The Venaria Reale”, Dott.ssa Paola Croveri, Dott. Marco Nervo, Dott.ssa Tiziana Cavaleri, Dott.ssa Anna Piccirillo, Dott. Daniele Demonte and Dott. Paolo Triolo.

Introduction

  • 1 The dimensions of the fragment of the mural painting are 68x50x1.7 cm (hxlxd).
  • 2 The dimensions of the fragment of the mural painting are208x193.2x2.1 cm (hxlxd).

1This paper deals with the conservation of two fragments of mural paintings from the painted decorations realized by Bernardino Luini for Villa Pelucca (Sesto San Giovanni), detached with the strappo method, and transferred onto wooden supports. The paintings are now in the Pinacoteca di Brera. The first painting, originally in the Sala Grande of the Villa, entitled  The prayer of Moses on Mount Sinai 1(ill.1); the second was located in the Gabinetto and entitled Venus and Adonins, and in the background the birth of Adonis2(ill.2).

Fig.1  The prayer of Moses on Sinai. Fragment of the mural painting detached with the strappo methodology

Fig.1  The prayer of Moses on Sinai. Fragment of the mural painting detached with the strappo methodology

On the left the front. On the right the back.

Photographic credits: © Gregori 2014.

Fig.2  Venus and Adonins, and in the background the birth of Adonis

Fig.2  Venus and Adonins, and in the background the birth of Adonis

Fragment of the mural painting detached with the strappo methodology

Photographic credits: ©Gregori 2014.

On the left the front. On the right the back.

2In 1821, the whole pictorial decoration of the Pelucca was detached by strappo technique by the restorer Stefano Barezzi and transferred onto wooden supports. These transfers can be considered examples of a technique typical for the experimental traditions of the nineteenth century. Most of the “estrattisti” (removers) used to keep  their working methods used  in the procedures of the strappo secret. Because of the transfer to a wooden support the paintings were exposed to further deterioration phenomena typical for panel paintings. Despite difficulties of political and technical nature, the paintings from the Pelucca were legally bought by the Pinacoteca of Brera on 8 July 1924.

Description of the paintings

3Through careful macroscopic observation of the surface of both paintings, it was possible to identify some key elements to understand the artist’s technique as well as to approach the procedures used by the restorer Stefano Barezzi during the transport of the paintings.
The sources show that the entire painting’s cycle was realized in fresco technique. Currently, some methodologies performed by Barezzi for the transport are still unknown, especially with respect to the subdivision in several portions of the painted surface: it is likely that the restorer, once he realized the technical difficulties he would have encountered, mainly due to the large size of the work of Venus and Adonis and in the background the birth of Adonis, decided to further fragment the paintings still on the wall during the operation of strappo. On the contrary, it is plausible to assume that similar technical difficulties would have led Barezzi to divide only at a second moment the painted surface, formerly entirely detached, into sections, in order to facilitate its adhesion on the wooden supports.

4The Prayer of Moses at Sinai is divided in two portions of detached mural paintings, whereas Venus and Adonis and in the background the birth of Adonis consists of sixteen pieces.

5The colour palette used by the artist from Milan mainly consists of earth pigments and pigments based on copper, for example, red earth, yellow ochre, green earth, burnt umber and malachite. The three garments of the female characters in Venus and Adonis and in the background the birth of Adonis present different tonalities of violet, depending on the “chiaroscuro” effects the artist wanted to obtain. Furthermore, in correspondence to the two women in the background, two signs of pentimenti have been noted on the painted surface (ill.3).

Fig.3  Pentimenti of Venus and Adonis, and in the background the birth of Adonis

Fig.3  Pentimenti of Venus and Adonis, and in the background the birth of Adonis

From left to right: with imaging to UV light and IR, performed on the same painting,  two pentimenti of the artist could be identified.

Photographic credits: Centro Conservazione e Restauro “La Venaria Reale”, 2014.

6In the lacunae it was possible to observe the dense weave of the canvas onto which the fragments of the paintings had been fixed. Thanks to the technical analysis of fabric, it has been possible to determine that the fibre is of vegetable origin, probably cotton, with a thread count of 38 per cm², and that the ends per inch are 38 per cm². Moreover it was possible to identify the lead white/gesso layer that was most likely used as an adhesive to attach the canvas to the back of the mural, as well as the canvas to the panel.

The state of preservation

7The state of preservation of the artworks is closely linked to the behaviour of the wooden supports, made of low quality fir tree planks, and to their cradle. The supports are deformed due to a non-homogeneous shrinkage of the two faces of the paintings. The planks of the support as well as the frame, made of wood from a broad-leave tree, present a diffuse attack of wood-boring insects, extended in some cases to the paint layers. Both panel paintings present several misalignments, splits and cracks of various dimensions. Some of them pass through the entire thickness of the panels, others do not (ill.4). The causes of such deterioration phenomena lay in the cradle that blocks the natural dimensional variations of the wood, creating splits corresponding to the most fragile areas.

Fig.4  The state of preservation of the artworks

Fig.4  The state of preservation of the artworks

From left to right, up and down: the planks of the support present a diffuse attack of wood-boring insects extended in some cases to the paint layers. Both panel paintings present several misalignments, splits and cracks of various dimensions.

Photographic credits: ©Gregori 2014.

8This kind of deterioration phenomena is linked to several factors: to the nature of the wooden panel itself, to the system of restraints, and to the thermo-hygrometric variations in the ambient environment. Moreover, the paint layers are extremely thin and closely follow the surface of the panels. In raking light, the grain of the wood and the direction of the fibres are visible. During the course of this research, it was possible to study the structure of the support.

9The prayer of Moses on Mount Sinai is composed of four planks cut tangentially, with their inner face towards the paint layer. In Venus and Adonis and in the background the birth of Adonis the structural analysis has turned out to be more difficult because of the several restoration treatments the work has undergone. The support is composed of five radial planks, cut tangentially with their inner face towards the paint layer. As a result of the examination of the position of the holes on the internal border of the back frame, and the traces of the nineteenth century nails, it has been possible to reconstruct the original structure of the support. The wooden planks were held together by an external back frame made of four longitudinal and oblique struts with mortise and tendon joints reinforced by wooden beams and nails (ill.5). Also on the front side, in correspondence with the borders, the impression of the back frame is visible.  It can be supposed that during the mounting on the new support, part of the paint layers had been glued not only to the panels but also on the external frame. The panel was reinforced by a system of constraints, subsequently removed and replaced by the present cradle. The cradle is composed of six upright boards glued and nailed to the original panel and seven crosspieces, probably once movable thanks to a system of small bridges.

Fig. 5 Venus and Adonis, and in the background the birth of Adonis. The structural analysis of wooden support

Fig. 5 Venus and Adonis, and in the background the birth of Adonis. The structural analysis of wooden support

From left to right, up and down: the cradle is composed of six upright boards glued and nailed to the original panel and seven crosspieces, probably once movable thanks to a system of small bridges. The wooden planks were hold together by an external backframe made of four longitudinal and oblique struts with mortise and tenon joints reinforced by wooden beams and nails.

Photographic credits: ©Scarpitti 2014.

The previous restorations

10Both paintings present several traces of previous restorations. An accurate examination and research in archival documents allowed the chronological sequence of the restoration treatments to be reconstructed. These treatments, visible on both paintings, were common to all artworks that are part of this cycle of decorations. The study of the wooden support reveals without any doubt two restorations that were performed on all paintings of this cycle. The first comprised the thinning and preparation of the surface with a rasping tool, while the second comprised the cradling of the panels.

11Accurate examination  of the mural painting entitled The prayer of Moses on Mount Sinai revealed residues of the adhesive used for fixing of six rows of cleats, intended to counteract the natural deformation of the support, minimizing its movement. During the second intervention, these cleats were removed in order to make space for the two vertical crossbars, screwed to the support. In the Venus and Adonis and in the background the birth of Adonis, the chronological listing of previous restoration interventions is more difficult. It is supposed that the first intervention consisted in the removal of the original wooden panel, excluding the wooden back frame on the perimeter, as this is a structural component of the panel. Later, the horizontal elements along the perimeter of the back frame were cut in order to reduce warping. Afterwards, the aim was to recreate the structural integrity of the panel. Historical sources tell us that in1976, the architect Bresciani performed a restoration of this painting with the proposal of closing the discontinuities of the panel with gesso fillings and reintegrate the lacunae with watercolour. Up to now, we don't have the documents that can help us date the intervention that consisted in the application of pieces of canvas in correspondence to the fissures and of six wooden struts, which were the direct cause for the reappearance of the cracks all over the panel. Another restoration, probably done in the 1970s, consisted of cradling the panel, applying seven mobile horizontal crossbars and eight vertical battens fixed to the panel with nails. The most recent intervention on both supports, done by the Studio Brambilla in 1990, was limited to the cleaning of the wooden surface with a weakly alkaline solution and a consolidation treatment with a synthetic acrylic resin. On the surface of the paintings it is possible to distinguish three different restoration treatments that all the paintings of the pictorial cycle of Luini have in common. The first was done by Barezzi after the operations of transfer and includes the borders of the painting. He repaired the missing parts with fillings made of gesso and animal glue and carried out the chromatic reintegration of all elements that had been lost during the detachment from the wall. The next intervention consisted of retouching with colours tempered in casein binder, now altered to brown tonalities. The third restoration was a general revision of the painted surface, proposing to unify the altered retouching. The intervention, done by the architect Bresciani, included the re-adhesion of the paint layer and of the canvas support to the wooden panels. Finally, the last treatment of the paintings by the Studio Brambilla in 1990, consisted of the consolidation of the detachments between support, preliminary layers and paint layer and in cleaning the paintings. During this cleaning, it was decided to partially remove the over paintings, as they had been strongly altered chromatically in the course of time, excluding those done by Barezzi in the area of the perimeter of the painting. Concluding the cleaning, a chromatic reintegration that took into consideration also the smallest traces of original colour was carried out, resulting in harmonizing the appearance of the painting. In those parts where it was possible to reconstruct the original pictorial contents, chromatically similar reintegration was implemented, whereas where this was impossible, a neutral tone was chosen.

Non-destructive examination methods and analyses

12A series of specific non-destructive examination methods and analyses was undertaken to identify the materials, the state of preservation of the two mural paintings and the previous restoration treatments.

13The first step was a preliminary photographic documentation, in visible, diffuse and raking light. This examination revealed the surface structure of the brushstrokes and made the chromatic reintegration carried out during past restoration treatments visible. Moreover, it was possible to identify the portions of painting removed from the original mural support by strappo technique and transferred. Lines of assemblage and the evidence of folding of the paintings during the strappo operation were observed. The Venus and Adonis and in the background the birth of Adonis presented some paint blisters corresponding to the areas where the  nails had fixed the original cradle in the 19th century.

14Afterwards, multi spectral examination with ultraviolet fluorescence (UV) and ultraviolet reflectance (UVR) was undertaken. The first examination technique revealed the preliminary drawing executed by brush by the artist and the cutting carried out by Barezzi to divide the painting areas prior to detachment. Moreover, the original pigments used by Luini could be determined, especially with respect to green and blue copper-based pigments. Furthermore, UV imaging provided evidence of deterioration, particularly abrasions and lacunae of various dimensions in the paint layer. Ultraviolet Reflectance examination was above all useful to compare the results with respect to identification of pigments.

15Infrared photography revealed the two pentimenti in the Venus and Adonis and in the background the birth of Adonis, and, with respect to the state of preservation of the paint layer, the abundant retouching that had been added in the course of previous restorations.

16False colour infrared photography (IR/FC) helped to identify original pigments, for example, in the red garments of Adonis and Moses, evidence of cinnabar was proven thanks to the typical response of yellow colouring in false colour. A further critical observation was made with respect to the violet garments of Venus and of the two women in the background. Even though three different tonalities of the colourings were observed, XRF confirmed the same chemical composition of the pigments. It was assumed that  the variations had been influenced by the different state of preservation of the three areas.

17For the macroscopic documentation of the surface of the paintings a digital portable videomicroscope was used. This examination revealed, in some cases, mixtures of colours. For example, with respect to the orange colour, a compact layer of red earth mixed with yellow ochre could be distinguished. Likewise, for the flesh paint red earth mixed with calcium carbonate (Bianco San Giovanni) could be demonstrated. This colour was used as a base for the finishing details "a secco", executed with cinnabar and an organic binder. Moreover, videomicroscopy allowed the observation in more detail of the discontinuities created by tears in the canvas that were only partially adhered to the support.

18Thanks to XRF (X-Ray Fluorescence) the chemical composition of pigments was specified, distinguishing as much as possible the original pigments from the areas where restoration treatments were carried out. A measurement was taken in correspondence with one of the lacunae confirming calcium: this result confirms the existence of traces (even if minimal) of the original ground layer composed of calcium carbonate.

19For example, on the face of Venus, sulphur and titanium where found; this implies the probable presence of a filling containing gesso and afterwards retouched, as the use of titanium can be demonstrated from 1920. In all points that were analysed, an elevated level of lead was demonstrated, suggesting an overall covering of the canvas with lead white used to mount a layer of canvas to the back of the detached fragments.

20Visible Near Infrared Fibre Optics Reflectance Spectroscopy (Vis-NIR FORS)  made a comparison and confirmation of the results obtained with XRF and multi spectral analysis possible on both artworks.

21Referring to the considerations expressed in the paragraph on the state of preservation of both paintings, it was necessary to monitor the deformations of the wooden supports. Periodically, the cracks and discontinuities of the surface were measured in several points with the aid of a calibre, in order to monitor the variations. Temperature and humidity data were also collected in order to have a reliable comparison. The results document a dimensional variation of the wood in correspondence to the discontinuities of both paintings between the first and the second measurement. From the third measurement it seems that these discontinuities return very slowly to their initial position. The transport to the CCR conservation laboratories disturbed the equilibrium state of the painting-environment system, provoking a sudden response of the wooden support. In the following months, the re-establishment of an equilibrium recreated the painting’s initial state of preservation. It is necessary to underline that the presence of deformations and discontinuities of the paintings are attributed to the local and fixed restrictions applied during previous restoration treatments.

22The structural elements and the distribution of the discontinuities of both works of art were examined with Radiography (ill.6).

Fig. 6 Radiography analysis

Fig. 6 Radiography analysis

On the left The prayer of Moses on Sinai and on the right Venus and Adonis, and in the background The birth of Adonis.

Photographic credits: Centro Conservazione e Restauro “La Venaria Reale”, 2014.

23In The prayer of Moses on Mount Sinai X-ray imaging exposed some features that had not been previously visible to the naked eye, for example, some defects of the panels. As the panel was made of coniferous wood we can note the location of knots, sometimes fractured and hidden by cross bars screwed to the support. With respect to the state of preservation of the materials used in previous restoration treatments, not only the galleries excavated by wood-boring insects were made visible, but also the techniques applied to close them in a previous intervention with sawdust and glue. Finally, X-ray imaging revealed the presence of a circular object under the upper left crossbar. As it is a historical piece of wood inserted into a hole; the most plausible explanation is that it might be connected to the origin of the panel, more precisely to the moment of transport of the wood. In the past, transporting trunks was facilitated by connecting each trunk to the other by means of strong chains. It is therefore assumed that this hole had been created in the part of the trunk where the chain was supposed to pass.

24Similarly, the support of the painting entitled Venus and Adonis and in the background the birth of Adonis consists of a panel of lower quality with numerous knots, almost all fractured and, with X-ray analysis, it was possible to follow the distribution of these fractures also underneath the cradling. This analysis revealed small nails in the splits, applied in an attempt to flatten the panel and adhere the v-shaped grooves of poplar wood. In addition, it is interesting to note the high number and the location of the nails that anchor the crossbars to the wood of the support.

25Fourier Transfer Infrared Spectroscopy (FT-IR) was used to verify the use of organic materials on the paint layer in the course of previous restoration treatments. It was possible to exclude any organic materials applied to the surface.

Destructive analysis

26In order to be able to study the materials and the technique of the transfer of the two fragments of mural paintings, and to determine the procedures and the materials to be used in conservation, it was necessary to undertake a further examination taking a microsample from Venus and Adonis and in the background the birth of Adonis.

27A sample that included all layers, from the wooden support up to the paint layer, was taken to identify the composition and the sequence of the preliminary layers, with a particular focus on the interface between the canvas lining and the paint layer,. The sample was embedded in transparent resin (epoxy resin Struers Epofix), then sandpapered perpendicularly to the external surface until a perfect cross section was obtained. With scanning electron microscopy the following stratigraphy could be observed (ill.7):

  • Paint layer with green earth

  • Priming layer consisting of lead white and gesso

  • Canvas backing

  • Priming layer consisting basically of gesso

  • Wooden support

28The information obtained by accurate visual examination, focussed bibliographic research, and non-destructive analyses was acknowledged by this last examination.

Fig. 7 Microsample from Venus and Adonis, and in the background the birth of Adonis

Fig. 7 Microsample from Venus and Adonis, and in the background the birth of Adonis

From left to right, up and down: With scanning electron microscopy the following stratigraphy could be observed.  

Photographic credits: Centro Conservazione e Restauro “La Venaria Reale”, 2014.

Preliminary considerations regarding the conservation and restoration treatment

29The results that were obtained during the analytical phase made it possible to select the materials to test for the treatment of the painting entitled The prayer of Moses on Mount Sinai.

30First of all, it was decided to start with a treatment of disinfestation by anoxia on both paintings because of the high number of holes caused by insect attack. Consequently, the paintings were kept in a controlled modified atmosphere over a period of thirty days.

31The phase of cleaning tests was preceded by microphotographic documentation accomplished with the help of videomicroscope and colorimetric imaging. The same documentation methods were repeated after concluding the tests in order to be able to monitor the effects of the interventions; after a first cleaning, which consisted in removal of dust and dirt depositions on the surface, the same areas were examined with ultraviolet light by means of portable Wood lamps in order to be able to identify the presence of residues and confirm their complete removal.

  • 3 The test focused on the materials presented and examined during a symposium organized by CESMAR (Ce (...)

32Due to the problem of the high fragility involving various solubility parameters for the priming layers and the reintegration done in course of previous restoration treatments, making it impossible to use aqueous or polar solvents, diverse dry cleaning systems were tested,  including rigid or semi rigid gel cleaning systems. Thanks to published research on this topic (Brokerhof et al., 2002; Raasschounielsen et al., 1978), to an accurate analysis of the state of preservation of the paintings and to the results of the research done by the Netherlands Institute of Cultural Heritage3, it was decided to use a smooth synthetic PVC-free eraser (during the aging processes, PVC frees hydrochloric acid which is particularly damaging for paint surfaces) in order to obtain a homogeneous cleaning of the whole surface. Following technical and scientific evaluations with Fourier Transfer Infrared Spectroscopy analysis, a non-abrasive medium density eraser was chosen, Faber-Castell PVC-FREE:

  • Faber-Castell PVC-FREE 7095-20: polybutadiene, sulphur, titanium and calcite; without PVC, chlorine and oils.

33The dry cleaning gave very good results: the paint layer wasn’t abraded by the mechanical operation of treating the surface with this eraser. After the cleaning test, the surface of the painting was examined closely with an optical microscope and in ultraviolet light. Both examinations showed good results as the morphology of the paint layer had not been damaged. Moreover, the colorimetric measurements done previously evidenced a brownish tone of dirt that diffused into yellow; after cleaning, the variations of trichromatic coordinates evidenced a slight change in direction of brown and a diminution of the yellow component.

  • 4 The AgarArt was made to swell in demineralized water to 3%.

34Next, a rigid gel, AgarArt, which has the high water-retaining capacity, was tested  in order to observe the impact of humidity on the surface4. It was applied without heating, with an application time of five minutes. However, in the lacunae, the gel caused swelling of residues of the adhesive used for the strappo (residual animal skin glue from the facing), chromatically altering the painted surface. Nevertheless, the results of the colorimetric measurements are very similar to those of the first cleaning test.

  • 5 The Gellano Kelcogel was made to swell in demineralized water to 3%.

35The third and last cleaning test was done by means of another rigid gel, the Gellano Kelcogel, which compared to AgarArt, is more transparent5. Also in this case the gel was applied without heating and for an application time of five minutes. Even if the visual monitoring of the cleaning was much better, the adhesion to the surface was poor due to the rigidity of the gel, and it was necessary to repeat the application several times. The colour luminosity parameter (ΔL) was highly significant for this cleaning test. The higher value of ΔE* (linked to a higher value of ΔL) confirmed indeed the visible results, namely a cleaning level that is to be deemed as too marked. After an careful observation of the behaviour of the tested materials it was decided to perform the cleaning exclusively by dry cleaning using the Faber-Castell PVC-FREE rubber (ill. 8).

Fig.8 The prayer of Moses on Sinai. Cleaning tests

Fig.8 The prayer of Moses on Sinai. Cleaning tests

From left to right, up and down: results of the cleaning tests before and after treatment.

Photographic credits: ©Gregori 2014.

36The treatment of the support of the painting entitled Venus and Adonis and in the background the birth of Adonis will result in  serious mechanical strain in the painting,   and will take longer than the restoration/conservation treatment of The prayer of Moses on Mount Sinai. For this reason some materials were tested to identify an appropriate temporary facing for the painted surface.

  • Test n.1: 70% cyclododecane in White Spirit, intermediate layer n. 1 foil of Japanese paper , top layer 2 % Tylose in deionised water.

  • Test n. 2: on the surface thin layer of 70% cyclododecane in White Spirit, top layer 5% Paraloid B72 in acetone applied by brush.

  • Test n. 3: on the surface medium layer of 70% cyclododecane in White Spirit, top layer 5% Paraloid B72 in acetone applied by brush.

  • Test n. 4: on the surface thick layer of cyclododecane in White Spirit 70%, top layer 5% Paraloid B72 in acetone applied by brush.

37The first test did not give good results as the removal of the facing adhesive also damaged the colour below (applied “a secco”). The combination of materials used in the other three tests were more efficient, especially the third one, as the acrylic resin as top layer on the thin layer of cyclododecane guaranteed a higher elasticity and duration of the consolidant, as it slowed down its sublimation process. In addition, good adhesion and cohesion of the painted surface could be observed. (ill. 9).

Fig.9 Temporary facing for the painted surface for Venus and Adonis and in the background the birth of Adonis

Fig.9 Temporary facing for the painted surface for Venus and Adonis and in the background the birth of Adonis

From left to right, up and down: results of temporary facing tests before and after the treatment.

Photographic credits: ©Gregori 2014.

38Despite the positive results of facing trials with respect to their mechanical behaviour, optical microscopy analysis showed residues of acrylic resin on the surface. The resin penetrated into the consolidation layer, which was meant to have an isolating function, and it came in touch with the paint layer. It will be necessary to do further testing, maybe using another solvent, in order to avoid any contact with the original surface.

Conservation and restoration of the Prayer of Moses on Sinai

39In order to create a secure environment for the artwork avoiding as much  mechanical strain as possible, the painting was laid face down on a horizontal surface previously prepared with various layers of softening protecting materials to safeguard the paint layer. Afterwards, the two crossbars were dismantled. Actually, in the area with more severe discontinuity, the lower plank was still connected to the rest of the support by a small bridge of fibres of a few millimetres. After having documented this area, it was decided to separate the two planks in order not to impede the subsequent adhesion (ill.10).

Fig.10 Conservation and restoration of the Prayer of Moses on Sinai

Fig.10 Conservation and restoration of the Prayer of Moses on Sinai

From left to right, up and down: dismantling of the two crossbars and separation of the two planks.

Photographic credits: ©Gregori 2014.

40After the dismantling of the crossbars, the support slightly deformed due to the removal of the strain accumulated over time caused by the rigid and fixed constraints, as well as due to a dimensional diminution of the back caused by a reduction of relive humidity of the environment. In order to create a favourable surface for the adhesion both internal faces of the planks were cleaned with a mixture of water and acetone 1:1 v/v. Subsequently, a special screw clamp system was developed with the purpose of finding the right level of assembling of the planks and creating a safe situation for the whole artwork. Next, the vinyl adhesive Bindan-Rs was applied by brush, and after joining the lower plank to the rest of the support, the same screw clamp system was adopted. The adhesion gave perfect results and therefore the next step was the consolidation of the central area of the split by inserting wedges of poplar wood, which has a similar texture to that of fir; the wood-fibres are very regular and compact, and due to its less marked grain, it is easily workable and presents homogenous surfaces for adhesion. The former holes for the cleats were filled with pine tree insertions, fixed to the support with carpenter's glue; the radial section of the wood laying parallel to the fibres of the support (ill.11). The next step was to fill the discontinuity on the top right angle using a very light and elastic acrylic filling, in which glass micro-spheres were mixed with acrylic resin. Because of its slightly alkaline pH it was buffered with a weak solution of acetic acid reaching a pH of 7.5, to exclude any negative interaction with the original materials. At that point, chromatic reintegration with watercolours of the inserts and fillings was completed, plus a dyeing of the insertions of pine wood with a dark water-based stain. Finally, both the frame and the support were treated with Permetrina applied by brush in order to prevent new insect attacks.

Fig.11 Conservation and restoration of the Prayer of Moses on Sinai

Fig.11 Conservation and restoration of the Prayer of Moses on Sinai

From left to right, up and down: consolidation of the central area of the split by inserting wedges of poplar wood. The former holes for the cleats were filled with pine tree insertions, fixed to the support with carpenter's glue.

Photographic credits: ©Gregori 2014.

  • 6 Paraloid B72 to 10% in acetone.
  • 7 This is a dark coloured gum on policloroprene base according to the ASTM D 1418-CR standard.

41The painted surface was dry-cleaned mechanically, using Faber-Castell PVC-FREE eraser, previously tested. This material removed superficial grime without compromising in any way the painted surface. Loose residual dirt on the surface was removed by vacuum or with a soft brush. The cracks caused by the knots and the holes caused by wood-boring insects, as well as the central part of the juncture on the bottom of the support were filled, using the same acrylic material described before. Cyclododecane was applied as temporary protection of the surface, and once the filling was completely dried, the residues of this protection were removed with Ligroin (petroleum ether). The fillings were reintegrated with watercolours. Here, it was necessary to evaluate some of the retouching done during the last restoration treatment by the Studio Brambilla. Some colours had changed and it was now necessary to partially remove them and reintegrate again with reversible materials (watercolours or pastels). Finally, a system of anchorage between the support and the wooden frame was developed. In order to provide stability for the painting and facilitate the gliding of the painting inside the frame it was decided to glue stripes of Tyvek to the borders along the internal perimeter using a acrylic resin6. Afterwards, the two long internal borders strips of nut wood were fixed with screws, after having been treated with biocides. Two strips of neoprene7 were glued in the space between the painting and the wooden strips. The use of neoprene was decided on because this is a material that cushions and tempers the natural movements of the wood without requiring a complex system with springs along the perimeter. It represents a simple technical solution that maintains the proper position of the support without bonds and permits a certain range of movement (ill.12).

Fig.12 Conservation and restoration of the Prayer of Moses on Sinai

Fig.12 Conservation and restoration of the Prayer of Moses on Sinai

From left to right, up and down: painted surface and wooden support before and after the restoration work.

Photographic credits: Centro Conservazione e Restauro “La Venaria Reale”, 2014.

Conservation project for Venus and Adonis and in the background the birth of Adonis

42Following a detailed technical and scientific analysis of the artwork, the state of preservation of the support as well as the state of cohesion and adhesion of the backing and paint layers were evaluated. The major set of problems consisted in finding the solution for the difficulties caused by the wooden support and its cradling.

43The high number of the original nails that anchor the crossbars to the wooden part of the support will make it very difficult to avoid future cracks in case of variations of environment relative humidity. This represents an inexorable constraint, also because a potential removal of the nails is impossible without damaging the paint layer and would mean the disconnection of the panel from the external frame, causing new and several discontinuities on the front.

44These considerations resulted in proposing a non-invasive treatment. After having guaranteed the protection of the painted surface, the structural continuity of the back will be recreated by trying to reduce the warping, and the discontinuities on the front will be filled with lightweight acrylic materials. Moreover, it will be necessary to construct a climate screen in order to reduce the exchange of humidity with the environment. The back could be sealed by filling the spaces in the cradle with balsa wood and finish with an external panel. Or, an additional frame could be applied externally to the existing one, for example, a compact closure of a polycarbonate panel fixed to the new frame, with the intention of permitting the viewing of the back of the painting. Following these operations, the cleaning of the surface will be done mechanically with dry sponges. Then, the chromatic reintegration of the painting and eventual revision of former interventions will be carried out.

Conclusions

45The present work focussed on issues regarding the complex interactions between wooden supports and two mural paintings transferred onto these supports. Furthermore, it has been possible to develop  and in one case also to put into practice - a conservation treatment with the aim of generating an adequate control system for the support, recreating structural continuity, cleaning the painted surface and enhancing its aesthetic presentation. In conclusion, this work, with its interdisciplinary characteristics, opens a way to further studies in relation to the development of correct methodologies and finding appropriate materials to treat the other 23 fragments of the series of Luini paintings transferred in the same way by strappo technique.

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Notes

1 The dimensions of the fragment of the mural painting are 68x50x1.7 cm (hxlxd).

2 The dimensions of the fragment of the mural painting are208x193.2x2.1 cm (hxlxd).

3 The test focused on the materials presented and examined during a symposium organized by CESMAR (Centroper lo Studio dei Materiali per il Restauro, a scientific organization that works in the field of conservation science applied to conservation and restoration of polychrome movable artworks) in cooperation with the University of Pavia and with the Cultural Heritage Agency of the Netherlands, under the direction of the franco –dutch conservator Maude Daudin-Scotte. The title of the symposium was: “Analysis and applications of dry cleaning materials on unvarnished paint surfaces” and it was held in Pavia in September 2012. The results have been published in 2014 in “Analysis and application of dry cleaning materials on unvarnished paint surfaces”.

4 The AgarArt was made to swell in demineralized water to 3%.

5 The Gellano Kelcogel was made to swell in demineralized water to 3%.

6 Paraloid B72 to 10% in acetone.

7 This is a dark coloured gum on policloroprene base according to the ASTM D 1418-CR standard.

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Table des illustrations

Titre Fig.1  The prayer of Moses on Sinai. Fragment of the mural painting detached with the strappo methodology
Légende On the left the front. On the right the back.
Crédits Photographic credits: © Gregori 2014.
URL http://ceroart.revues.org/docannexe/image/4924/img-1.jpg
Fichier image/jpeg, 824k
Titre Fig.2  Venus and Adonins, and in the background the birth of Adonis
Légende Fragment of the mural painting detached with the strappo methodology
Crédits Photographic credits: ©Gregori 2014.
URL http://ceroart.revues.org/docannexe/image/4924/img-2.jpg
Fichier image/jpeg, 568k
Titre Fig.3  Pentimenti of Venus and Adonis, and in the background the birth of Adonis
Légende From left to right: with imaging to UV light and IR, performed on the same painting,  two pentimenti of the artist could be identified.
Crédits Photographic credits: Centro Conservazione e Restauro “La Venaria Reale”, 2014.
URL http://ceroart.revues.org/docannexe/image/4924/img-3.jpg
Fichier image/jpeg, 396k
Titre Fig.4  The state of preservation of the artworks
Légende From left to right, up and down: the planks of the support present a diffuse attack of wood-boring insects extended in some cases to the paint layers. Both panel paintings present several misalignments, splits and cracks of various dimensions.
Crédits Photographic credits: ©Gregori 2014.
URL http://ceroart.revues.org/docannexe/image/4924/img-4.jpg
Fichier image/jpeg, 712k
Titre Fig. 5 Venus and Adonis, and in the background the birth of Adonis. The structural analysis of wooden support
Légende From left to right, up and down: the cradle is composed of six upright boards glued and nailed to the original panel and seven crosspieces, probably once movable thanks to a system of small bridges. The wooden planks were hold together by an external backframe made of four longitudinal and oblique struts with mortise and tenon joints reinforced by wooden beams and nails.
Crédits Photographic credits: ©Scarpitti 2014.
URL http://ceroart.revues.org/docannexe/image/4924/img-5.jpg
Fichier image/jpeg, 300k
Titre Fig. 6 Radiography analysis
Légende On the left The prayer of Moses on Sinai and on the right Venus and Adonis, and in the background The birth of Adonis.
URL http://ceroart.revues.org/docannexe/image/4924/img-6.jpg
Fichier image/jpeg, 388k
Titre Fig. 7 Microsample from Venus and Adonis, and in the background the birth of Adonis
Légende From left to right, up and down: With scanning electron microscopy the following stratigraphy could be observed.  
Crédits Photographic credits: Centro Conservazione e Restauro “La Venaria Reale”, 2014.
URL http://ceroart.revues.org/docannexe/image/4924/img-7.jpg
Fichier image/jpeg, 920k
Titre Fig.8 The prayer of Moses on Sinai. Cleaning tests
Légende From left to right, up and down: results of the cleaning tests before and after treatment.
Crédits Photographic credits: ©Gregori 2014.
URL http://ceroart.revues.org/docannexe/image/4924/img-8.jpg
Fichier image/jpeg, 608k
Titre Fig.9 Temporary facing for the painted surface for Venus and Adonis and in the background the birth of Adonis
Légende From left to right, up and down: results of temporary facing tests before and after the treatment.
Crédits Photographic credits: ©Gregori 2014.
URL http://ceroart.revues.org/docannexe/image/4924/img-9.jpg
Fichier image/jpeg, 660k
Titre Fig.10 Conservation and restoration of the Prayer of Moses on Sinai
Légende From left to right, up and down: dismantling of the two crossbars and separation of the two planks.
Crédits Photographic credits: ©Gregori 2014.
URL http://ceroart.revues.org/docannexe/image/4924/img-10.jpg
Fichier image/jpeg, 804k
Titre Fig.11 Conservation and restoration of the Prayer of Moses on Sinai
Légende From left to right, up and down: consolidation of the central area of the split by inserting wedges of poplar wood. The former holes for the cleats were filled with pine tree insertions, fixed to the support with carpenter's glue.
Crédits Photographic credits: ©Gregori 2014.
URL http://ceroart.revues.org/docannexe/image/4924/img-11.jpg
Fichier image/jpeg, 624k
Titre Fig.12 Conservation and restoration of the Prayer of Moses on Sinai
Légende From left to right, up and down: painted surface and wooden support before and after the restoration work.
Crédits Photographic credits: Centro Conservazione e Restauro “La Venaria Reale”, 2014.
URL http://ceroart.revues.org/docannexe/image/4924/img-12.jpg
Fichier image/jpeg, 908k
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Pour citer cet article

Référence électronique

Giulia Gregori, « Conservation and restoration of two wall painting fragments by Bernardino Luini  », CeROArt [En ligne], 5 | 2016, mis en ligne le 17 mars 2016, consulté le 25 mai 2017. URL : http://ceroart.revues.org/4924

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Auteur

Giulia Gregori

Giulia Gregori, born in 1989 in Turin, hold amaster's degree in Conservation and Restoration of Cultural Heritage from the University of Turin in agreement with the CCR “La Venaria Reale”, with a specialization indecorated surfaces of architecture. As soon as she graduated, obtained an internship contract at CCR funded by scholarship from the Foundation Cologni of Milan. From December 2015, she is working as Assistant of the Registrar at the Egyptian Museum of Turin.

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Licence Creative Commons
CeROArt – Conservation, exposition, restauration d'objets d'arts est mis à disposition selon les termes de la licence Creative Commons Attribution - Pas d'Utilisation Commerciale - Pas de Modification 4.0 International.

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