La Medusa by Caravaggio: characterisation of the painting technique and evaluation of the state of conservation

The oil painting “La Medusa” executed by Caravaggio at the end of the XVI century on a wooden shield, was investigated by integrated physical–chemical and analytical methodologies in order to obtain scientific data capable of elucidating the state of conservation and the painting technique. Optical (OM) and electronic (SEM-EDS) microscopy, micro-FT-IR spectroscopy, gas chromatography–mass spectrometry (GC–MS) and pyrolysis GC–MS were applied on two microfragments and some organic samples obtained by solvent extraction using the swab cleaning technique. The obtained results indicated that Caravaggio probably reused an old shield as a previous gypsum preparation layer has been detected under the original painting layers. He used white lead, natural earths, verdigris and lead–tin yellow type I mixed with drying oils to paint. The considerable amount of amorphous particles of copper chlorides found in the green pigment verdigris suggests that it could have been produced according to the ancient recipe of verde salsum described by Theophilus. Mordant gilding has been identified on the upper part of the shield that can be related to an abandoned experiment to give the painting a mirror-like reflecting effect. Three different varnishes layers have been detected above the painted surface. The original and restoration varnishes have been identified and they contain a mixture of drying oil, mastic and turpentine and some beeswax. Cleaning tests, performed with different organic solvents, suggest the use of isopropyl alcohol as cleaning agent because it is less efficient in comparison to others solvents; thus it ensures a careful and controlled removal of the varnishes.     

The funerary klinai of tomb 1 from Amphipolis and a sarcophagus from ancient Tragilos, eastern Macedonia: a physico-chemical investigation on the painting materials

Optical and SEM-EDS microscopy, X-ray powder diffraction and micro FT-IR spectroscopy investigations of the funerary klinai (couches) of Tomb 1 from Amphipolis and a stone sarcophagus from ancient Tragilos—two painted monuments made by Macedonian craftsmen of the Early Hellenistic period—identified the original materials and painting technique, as well as synthetic materials used as consolidants during past restoration treatments. The original organic binders and the superficial modern coatings have been identified by micro FT-IR spectroscopy applied directly to the sampled powders or tiny fragments and to their solvent—soluble fractions. The pigments identified on the couch of Amphipolis are: red and yellow ochre, cinnabar, Madder lake, paratacamite and antlerite, carbon black, calcium carbonate, kaolin and gypsum. The identification of egg and animal glue confirms the application of tempera and secco techniques. The detection of polymers such as polydimethylsiloxane, polyvinyl acetate and alkyd resins, is related to modern restoration products. The pigments attested on the paintings of the Tragilos' sarcophagus are: red and yellow ochre, Egyptian blue, malachite, carbon black, calcium carbonate and gypsum. The absence of organic binders combined with the constant presence of calcium carbonate in all the examined samples suggests the use of lime as the binding medium in the painted decoration of the sarcophagus. The presence of Paraloid B72 is related to recent conservation treatments.     

Teodelinda's tales at Monza Cathedral: A physico-chemical diagnosis of the pictorial cycle

The pictorial cycle “Teodelinda's Tales” at Monza Cathedral, painted by Zavattari and his sons in 1444–1446, has been investigated by optical and SEM-EDS microscopy and microFT-IR spectroscopy. Paint layers, gildings and other metallic decorations have been analysed to elucidate the execution technique, the state of conservation and the possible retouchings in consequence of deterioration processes. Organic binders, coatings and adhesives have been also identified especially by microFT-IR spectroscopy applied directly to the sampled powders or fragments and to their solvent–soluble fractions. The obtained data offer a correct and satisfactory knowledge of the original organic and inorganic materials and those used in the subsequent retouches and restorations, their state of conservation and the painting techniques (fresco, mezzo fresco and secco).The physico-chemical investigations allowed to identify the nature and sometimes the provenance of the employed materials (i.e. ultramarine blue pigments) and some decay markers, particularly useful in understanding and describing the cycle realised by the authors and the modifications suffered along the centuries, and also to propose an integrated methodology for the scientific study of the mural paintings.     

A new family of high viscosity polymeric dispersions for cleaning easel paintings

The procedures for making and applying a new family of high viscosity aqueous polymeric dispersions based on poly(vinyl alcohol)-borax (PVA-borax) matrices are presented. A specific system of this type has been used to remove an oxidized varnish coating from the surface of “Coronation of the Virgin with Saints”, a 15th century egg tempera painting on wood by Neri di Bicci (Florence, 1418–1492). FTIR spectra showed that the oxidized varnish was constituted of highly aged shellac resin. Good cleaning performance was attained when the liquid portion of the dispersion consisted of a mixture of water and acetone. Rheological investigations indicate that the acetone content does not affect the mechanical properties of the polymeric dispersion. Those mechanical properties permit easy removal of the cleaning agent simply by peeling it from the surface by means of a forceps or spatula once it has carried out its cleaning function. Optical microscopic and FTIR investigations show that the cleaning agent is able to remove the oxidized varnish coating from the surface of the Neri di Bicci painting without leaving detectable residues.     

Laser cleaning of terracotta decorations of the portal of Palos of the Cathedral of Seville

Laser cleaning has been used to restore the soiled terracotta statues and decorations of the tympanum of the portal of Palos of the Cathedral of Seville in Spain. A simultaneous laboratory study performed on a representative sample helped to identify the optimum laser conditions to remove the dark soiling layer produced by air pollution. It was found that irradiation at 1064 nm with a Q-switched Nd:YAG laser was more effective than the harmonic wavelengths of 532 or 266 nm. LIBS and Raman microscopy gave information on the composition of terracotta and identified the presence of a protective layer made of gypsum and calcite. As detected by Raman spectroscopy, laser irradiation caused the elimination of the carbon component of the soiling layer and the appearance of an anhydrite component in the laser irradiated gypsum layer applied over the terracotta substrate for protective purposes. Local heating of the surface caused by laser irradiation at 1064 nm, the laser wavelength used for restoration of the portal, might be responsible for a process of partial dehydration of gypsum into anhydrite.     

The binding media of the polychromy of Qin Shihuang's Terracotta Army

The “Terracotta Army” is a worldwide known archaeological finding in China. It is a part of the burial complex of the emperor Qin Shihuangdi (259–210 BC), which is still under excavation and study. The fact that the sculptures, chariots and weapons of the First Chinese Emperor's Terracotta Army were originally all painted in bright colours is still not widely known. The chemical characterisation of the paint medium was performed through an analytical procedure based on GC-MS. The proteinaceous binder was identified for the first time through a desalting procedure used in proteomics. The identification of egg as a paint binder is extremely interesting in terms of the historical significance of the work of art itself and important in terms of the method of conservation. Moreover it represents one of the first steps towards an understanding of the painting technique used on ancient sculptures in China, of which – despite their fame – nothing is yet known.     

Experimental tests used for treatment of red weathering crusts in disintegrated granite – Egypt

Rock weathering is defined as the process of rocks alteration as a result of the adjustment of its internal constituents by the action of physical, chemical and biological factors, to the prevailing conditions of the atmosphere and in the environment. In humid polluted areas “red weathering” is one of the major deterioration forms that characterize most granitic rocks. Several intervention steps are required to remove and treat all surfaces affected by this form. It is one of the most aggressive forms of deterioration which are essentially composed of some complex species of clay minerals “Kaolinite, Illite, Montmorillonite and Tosudite”, in addition to some species of salts as “Gypsum” pigmented by “Hematite” as a colorant. After several investigatin techniques, these crusts need several intervention and conservation steps to remove and eliminate the aggressive effects resulted from the red crusts through three essential steps: “cleaning, gap filling and strengthening and stabilizing”. After evaluating all materials and methods that were performed by “DBN, SEM, EDX, and AAS”, the present study suggests that the most suitable cleaning methods are composed of three essential steps “dry and vacuum cleaning (DVC), ultra-sonic cleaning (USC), poultice cleaning (PC)”. Furthermore, the elected gap filling material composed of “Araldite AY-103” mixed with “Granite powder as petro-filler.” Finally, different evaluation methods proved that “Wacker H” is the most suitable strengthening and stabilizing material for consolidation purpose.     

Pigments and binders in “Madonna col Bambino e S. Giovannino” by Botticelli investigated by micro-Raman and GC/MS

During the restoration plan of the famous painting “Madonna col Bambino e S. Giovannino” by Sandro Botticelli, located in the Museo Civico of Piacenza (Italy), a study on painting materials was carried out. The pigments, the binders and the materials used for the application of ground and priming layers were studied using micro-Raman spectroscopy, gas chromatography coupled with mass spectrometry (GC/MS), optical and electronic microscopies. Gypsum and anhydrite were found in the ground layer, while carbon black and lead white were used in the priming layers. The precious pigments of the artist's palette and the binders used (egg and animal glue) were determined.     

The scientific investigation for the study and conservation of the wooden model of S. Maria della Consolazione's church (Todi,Italy)

The focus of this work is the wood polychrome model of the church of S. Maria della Consolazione in Todi, an artefact whose author and historical events are not completely known except a general reference to the construction period of the church (1508–1607 AD). In this study, original and additional materials were examined in order to provide a deeper understanding of the painting and assembly techniques, and a greater awareness of how well preserved the object is, as well as an analysis of previous preservation and conservation interventions. The samples from the painted surfaces were examined by means of micro-Raman spectroscopy, fourier transform infrared (FTIR) spectrometry and internal microstratigraphic analysis. Thin sections of the wood samples were examined under an optical transmission light microscope in order to identify the botanical species. The results shown in this paper suggest the possibility that the original painted layers are made of calcium carbonate white, red ochre and indigo and they were applied by protein binder without any ground layer. Some non-original pigments were found on the model surface like Prussian blue and chrome yellow. Concerning wood components, poplar was characterized both in the original and non-original parts of the model whereas pine species were detected only in the restoration elements.     

A color image segmentation method as used in the study of ancient monument decay

In the cultural heritage area, it is of fundamental importance to characterize and classify the conservation state of the materials constituting ancient monuments, in order to study and monitor their decay. Generally, the decay diagnosis is provided by “naked eye” analysis done by expert scientists “walking around” the artifact and recording the conservation state of each individual element they observe. In this paper, a color image segmentation approach, based on histogram threshold and edge detection techniques is presented, to extract degradation regions, characterized by holes or cavities, from color images of stone-materials. The goal is to provide an aid to the decay diagnosis by segmenting degraded regions from color images, computing quantitative data, such as the area and perimeter of the extracted zones, and processing qualitative information, such as various levels of depth detected into the same zones. Since color is a powerful tool in the distinction between objects, a segmentation technique based on color, instead of intensity only, has been used to provide a clearer discrimination between regions. The study case concerns the impressive remains of the Roman Theatre in the city of Aosta (Italy). In particular, we have processed and analyzed some color images of the theatre puddingstones, acquired by a camera.     

Painting technique and state of conservation of wall paintings at Qusayr Amra,Amman – Jordan

The state of conservation of the frescoes at Qusayr Amra was investigated by integrated physico-chemical measurements, particularly optical and scanning electron microscopy, μ-infrared spectroscopy, mass spectrometry and X-ray powder diffraction.The frescoes appear darkened and severely damaged owing to the deterioration of surface treatments and to the widespread presence of different salts. These caused significant detachments of the painting layers.The materials used in the painting and preparation layers and in the wall plaster were characterized in order to clarify the painting technique. Different pigments have been identified on the pictorial layers: the original ones correspond to green earth, yellow and red ochre, realgar, bone black and lapis lazuli and others, such as titanium white and cobalt blue, ascribed to recent restoration works. Proteinaceous materials (egg or yolk) have been identified as binders for the pigments, indicating a tempera painting technique.Three different products, belonging to restoration interventions, have been also identified: the natural product shellac, ascribable to next-to-last restoration and scarcely removed during last restoration also because of its insolubility, the synthetic vinyl acetate and acrylic polymers. Particularly the latter one indicates an on-going degradation of the applied fixatives.The extensive deterioration of the surfaces is also due to the widespread presence of salts, such as chloride, nitrate and sulphate clearly identified by XRD measurements.The obtained results give a comprehensive overview on the employed painting technique and its state of preservation and on the causes of the painting deterioration. Therefore, they are a fundamental tool to develop durable and compatible materials and methodologies for a future conservation strategy of this site.     

A new class of gels for the conservation of painted surfaces

The application of a new class of organogels as cleaning tools for painted surfaces is described. It combines some of the most attractive features of cleaning liquids and normal gels while diminishing the deleterious characteristics of both. Thus, the ‘latent’ gellant, polyethyleneimine (PEI), reacts with CO₂ at room temperature in solutions of several organic liquids to produce an ammonium carbamate form (PEICO₂). This charged species organizes itself into 3D polymer networks which immobilize the liquids as gels. The properties of the original solution (i.e. a free-flowing liquid) are re-established immediately after addition of a small amount of a weak acid which displaces the CO₂ molecules and makes the PEI chains positively charged. The visual changes are substantiated by rheological analyses. Results from analytical tests to determine the utility of these gels as cleaning tools for painted surfaces of historical and artistic interest, have been obtained from contact angle and FTIR measurements as well as visual comparisons of the surfaces before and after application of the gels. The analyses indicate that the PEICO₂-based organogels were very effective in removing different surface patinas from painted supports. A surface layer of dammar was completely removed from a test canvas with oil paint, an aged painting from the XIX century, and a XV century oil-on-wood panel attributed to Mariotto di Cristoforo. Finally, a surface acrylic polymeric resin (used in a restoration performed during the 1960s) was also successfully removed from Renaissance wall paintings decorating the Santa Maria della Scala Sacristy in Siena, Italy. The isothermally rheoreversible gel approach described in this work represents a new, highly versatile, and very efficient method for removing aged surface patinas from works of art.     

A study on a set of drawings by Parmigianino: integration of art-historical analysis with imaging spectroscopy

Due to the extreme fragility of paper-based artefacts, few techniques are available for scientific investigation and characterisation of ancient drawings or paper-based artefacts. Image reflectance spectroscopy represents an almost unique tool for scientific analysis on precious drawings, for which even micro-invasive techniques of analysis cannot be used. Indeed, beside the high fragility of the support, drawings and graphical works are typically characterised by a very limited number of artistic materials, which in principle could give information on the work of art. In this paper an interdisciplinary study on a set of drawings by Parmigianino (1503–1540), selected from the collection of the Uffizi Gallery in Florence, is presented. Non-invasive measurements of image spectroscopy (IS) have been employed to support the work of art-historians in the critical re-examination and interpretation of the graphical work of the artist. The multispectral analysis has been carried out over the extended spectral region (400–1700 nm), in order to provide simultaneous indications both on the pictorial materials and on possibly underlying hatches. The data processing has been performed by means of Principal Component Analysis (PCA) and the elaboration of each case has been addressed to specifically respond to questions related to the art-historical problem.     

Environmentally-induced stone decay: the cumulative effects of crystallization–hydration cycles on a Lincolnshire oopelsparite limestone

An investigation has been undertaken at St Andrew’s church, Walpole St Andrew, Norfolk, to establish the underlying causes of the observed stone decay to the upper parts of the six stone piers. The stone decay was first recorded in the early 1930s. The salt-contaminated masonry within the church has been shown to undergo severe salt decay during the summer, with little damage occurring over the winter months. The south aisle piers have been shown to decay 2.5 times faster than the north aisle piers. Although crystallization–hydration cycles have been identified, the rate of decay is at its greatest when the cycling is relatively infrequent. This was not the expected trend. Furthermore, it has been shown that during extended periods where the ambient relative humidity is less than 75%, the rate of decay reaches a maximum. It is the length of this ‘drying’ period that apparently has the greatest influence on the rate of decay and could explain the significant difference in the rate of decay between the south and north aisle piers. The results have serious implications for passive conservation, where it is often recommended to lower the ambient relative humidity to well below the equilibrium relative humidity of the salt contaminant, to avoid crystallization–hydration cycles. Since, at the time of building, the church was situated on the coast, it is possible that the sodium chloride contamination occurred during the building process (1440–1520), particularly since the area was prone to sea-flooding at this time. Alternatively, the salt could have been applied as a treatment during the general restoration of 1897. Whatever the source of the salt, it seems likely that the ambient environment was changed by the insertion of a sealed floor in 1897, which could account for the onset of the salt decay.     

Elemental analyses by laser induced breakdown spectroscopy as restoration test on a piece of ordnance

Laser induced breakdown spectroscopy was used to investigate the composition of a gun found in the Adriatic seabed and kept in the “S. Castromediano” Provincial Museum in Lecce (Italy). Optical emission spectra of the laser-induced plasma from the surface of the piece of ordnance were recorded before and after its restoration. The metal alloy of the gun was determined through the identification of characteristic atomic emissions and confirmed through microanalysis carried out by energy dispersion X-ray spectroscopy. Experimental results evidenced that the gun is of bronze and revealed that elements composing the encrustation and noxious for the object conservation, such as calcium, were removed successfully during the cleaning operation. Performed elemental analyses confirmed that laser induced breakdown spectroscopy is a useful diagnostic tool to test the restoration degree of artworks.     

mtDNA analysis of the human remains buried in the sarcophagus of Federico II

The sarcophagus containing the remains of Federico II, located in the Cathedral of Palermo (Sicily, Italy), was opened on 1998 to perform a multidisciplinary survey [1]. Next to the remains of Federico II and in close contact with them were laying two other skeletons belonging, according to historical records, to Pietro II di Aragona and to an anonymous person (“The Third Individual”), probably a woman. The bones appeared severely deteriorated. Chemical analysis performed on bone samples excluded that the bodies underwent some kind of embalming process. The analysis of mtDNA from bone samples taken from the three skeletons was successful in only one of the two labs involved. The HVR1-mtDNA sequence (region: from nt 16,035 to nt 16,395), obtained from the bone samples of Federico II and “The Third Individual” appear identical but bear double peaks at the same nucleotide positions, suggesting mixing (i.e. contamination) of different mtDNA types. The HVR1 sequence obtained from the bone sample of Pietro II di Aragona does not present double peaks and differ from the Cambridge Reference Sequence (CRS) at six nucleotide positions. Cloning experiment of the Federico II amplicon demonstrated that the mixed mtDNA types are only two: one identical to CRS, the other identical to the sequence of Pietro II di Aragona. A reconstruction of these data are proposed in the Discussion. Due to the problematic context in which this study was carried out (mixed and deteriorated biological material, failure to replicate results in two different labs), our results and reconstruction can only be offered on a tentative basis. It is hoped that the data presented in this study will reveal useful, for future comparison, if further molecular genetics research will be carried out on the royal dynasties that ruled Sicily in the early centuries of the past millennium.     

Non-invasive spectroscopic measurements on the Il ritratto della figliastra by Giovanni Fattori: identification of pigments and colourimetric analysis

The painting Il ritratto della figliastra (Portrait of the Stepdaughter) by Giovanni Fattori (1889, Gallery of Modern Art, Pitti Palace, Florence) was investigated using non-invasive fibre optics reflectance spectroscopy (FORS). The use of compact and transportable instrumentation made it possible to easily record spectra of the polychrome surface at the restorer’s atelier during the restoration work. The results of colour analysis before and after the cleaning procedure of the painting are reported and discussed, together with an attempt at pigment identification.     

A post-Byzantine icon of St Nicholas painted on a leather support. Microanalysis and characterisation of technique

The pigments, organic materials and techniques used on a post-Byzantine icon of St Nicholas were determined by means of several micro-analytical techniques. The icon painter covered the leather support with silver leaf about 3 μm thick to create a smooth working surface. Animal glue was used to secure the leaf to the leather, and FTIR spectroscopy has identified another layer, 30–60 μm thick, of the same material applied as a primer above the silver. Above that, a layer of lead white covering the entire surface creates a white substratum serving the same purpose as the gesso on a wood panel. The colour palette, determined by means of scanning electron microscopy and FTIR spectroscopy, is very simple. Only seven colours were identified: lead white, caput mortuum, red and yellow ochre, cinnabar, carbon black and smalt. As far as we know, this is the first time that smalt has been found on a Byzantine icon. Since smalt was chemically synthesised only after 1500 AD, it may be concluded that this icon was painted after the end of the 15th century. Beeswax was used as a protective varnish.     

The glass-melting furnace and the crucibles of Südel (1723–1741, Switzerland): provenance of the raw materials and new evidence of high thermal performances

Fifty crucible fragments and 10 fragments of the melting furnace of the forest glassworks of Südel (1723–1741, Ct. Luzern), were analyzed by petrographic, mineralogical and chemical techniques in order to assess the temperature reached in the melting chamber and to find out which raw materials were used to make the crucibles and the melting furnace. Since the crucibles were used in the melting furnace, the temperature estimations were based on both the crucibles and the refractory fragments, as they were parts of the same system. The temperature range in the melting chamber, estimated by the structural order of the new-formed cristobalite, points to a temperature range between 1350 and 1500 °C. However, three crucible samples recorded extreme temperatures as high as 1650 °C, suggesting very high flame temperatures for wood fuel. The analyzed red bricks were made with local calcium-poor clay. One of them was tempered with refractory fragments, demonstrating an in-house production and the recycling of such a material after its use. The crucibles and the refractory bricks were made with the same refractory clay. The former using unprocessed clay and the latter blending clay with chamotte. A comparison with Sidérolithique clayey sand samples from the Swiss Jura, shows strong affinities which may rule out the archaeological hypothesis of an exclusive provenance of such clays from Germany, suggesting an import from the Swiss Jura mountains.     

Mosaic floors of roman Villa del Casale: Principal component analysis on spectrophotometric and colorimetric data

Spectrophotometric and colorimetric data obtained during a measurement campaign aimed at supporting the Roman “Villa del Casale” (Piazza Armerina, Sicily, Italy) conservation activities, are presented. Special attention was paid to the possible variation of the chromatic coordinates, possibly due to the interventions of cleaning, consolidation, and protection. Data have been analyzed by the Principal Component Analysis (PCA) statistical technique, with the attempt to investigate its role in data variability reduction and verify its effectiveness in interpreting the phenomena occurring on the mosaic surface of the Villa, through grouping the observations into homogenous clusters. Effectiveness in the use of the information provided by the spectrophotometric and colorimetric analyses is strongly related to the immediacy and ease of data reading by the restoration operators for whom the issues concerning the color measurement and its representation are often unfamiliar. This paper analyses data of different mosaic tesserae before/after the cleaning intervention and presents data clustering with PCA. This statistical technique has provided a synoptic scheme capable of improving data interpretation concerning the chromatic behavior of the materials. Moreover, the cluster distribution highlighted by the multivariate analysis made it possible to identify, more clearly, the parameters that mostly contribute to the chromatic shift and to monitor the behavior of variously colored tesserae.