A Mössbauer study of some coloured marbles (cipollino mandolato, rosso antico and fior di pesco): implications on the nature of their colour

⁵⁷Fe Mössbauer spectroscopy permits an explanation of the formation of the iron-bearing species present in three types of coloured marbles, known as cipollino mandolato, rosso antico and fior di pesco. Structural Fe²⁺ and Fe³⁺ located in silicates, together with the remains of weakly ferromagnetic hematite, arise from primary sediments. Fe²⁺ located in carbonates and anti-ferromagnetic hematite are formed by redox processes during marble formation. The relative contents of the iron species in the three types of marbles depend on the composition of the primary sediments and on local conditions during metamorphism. Knowledge of the type and amount of the iron species in marbles may help in the reconstruction of the redox processes, which took place during marble formation. The deviations of the Morin transition of the hematites play the role of genetic indicator because purity, crystallinity and the red hues of hematites in marbles can be related to the environment of formation.     

Volubilis (Meknes,Morocco): Archaeometric study of the white and coloured marbles imported in the Roman age

The ruins of the Roman town of Volubilis, located in the Middle Atlas, near Meknes, between Fez and Rabat, constitute the most important Roman archaeological site in Morocco and are included in the UNESCO World Heritage List. Volubilis became the headquarters of the Mauritania Tingitana limes after the annexation of the kingdom of Mauritania to the Roman Empire in AD 42. Evacuated by the Romans after the second half of the 3rd century, the town became the capital of the kingdom of Idriss I in AD 789.The results of an archaeometric study of the marbles imported into Volubilis during the Roman age are reported herein the sixth framework program of the European Union.Of the few coloured lithotypes that have been found, all are of Greek origin with the exception of the so-called “Portuguese pink”, a pale pink marble exploited by the Romans near Vilaviçosa in the Lusitania which, till now, has not yet been identified outside Iberia. As regards the white marbles employed in the statuary, petrographic study in thin section and the δ¹³C and δ¹⁸O isotopic data emphasize the frequent use of Lunense and Pentelic marbles. The latter also features among the white marbles used for crustae and architectural elements together with the dolomitic variety of Thasian marble, Parian marble from Lakkoi, Proconnesian marble from the island of Marmara, an unknown marble most probably of local origin, and a variety of the so-called “greco scritto” whose provenance still remains unclear. In fact, its petrographic and geochemical features do not match those known for the classical “greco scritto” from Cap de Garde, near Annaba (Algeria).     

Archaeometric and geological constraints for the provenance of carbonatic breccias used in monumental works along the Flaminia Consular Road (Umbria-Marche, Central Italy)

Along the Umbria-Marche stretch of the Flaminia Consular Road (220 B.C.) several archaeological finds of the most important monumental works, are well preserved. The stones, employed to build many bridges, substructions and sewerages, are represented by carbonatic breccias whose geological environment of formation and source areas had never been established. On the basis of mineralogical, petrographic and micropalaeontological analyses, two groups of these lithotypes employed in Roman age were distinguished: “monogenic carbonatic breccias” only constituted by clasts of the Maiolica Unit (Late Jurassic – Early Cretaceous) and “polygenic carbonatic breccias” made of fragments (in different proportions) of Calcare Massiccio (Early Jurassic), Corniola (Early Jurassic), Maiolica (Late Jurassic – Early Cretaceous) and Scaglia Rossa (Late Cretaceous – Early Paleogene) Units. The possible source areas of the breccias are compatible with stratified slope-waste to scarp-base deposits of periglacial origin belonging to the Upper Pleistocene. In particular, among the seven investigated areas, we pointed out the most probable provenances (Monte Faeto-Colle, Costacciaro, Scirca, Foci, Secchiano) along the flanks of the Apennine Mesozoic chain of the Umbria and Marche regions. Although the Romans could have exploited the whole thickness of some outcrops (now disappeared) of these carbonatic lithotypes at the deepest part of the valleys, we have constrained a local provenance of the breccias so commonly used in the monumental works of the Flaminia.     

Swelling damage in clay-rich sandstones used in the church of San Mateo in Tarifa (Spain)

This study shows that the sandstone used in the construction of the Church of San Mateo in Tarifa (Cádiz, Spain) is highly sensitive to processes of decay because of a combination of factors that are intrinsic and extrinsic to the material. The mineralogy, texture and porous system of the sandstone and the proximity of the church to the sea all play a part in these processes. X-ray diffraction reveals that there are interstratified chlorite/smectite clays among the minerals that make up the rock. These mixed layer clays have been shown to undergo hydric expansion. This phenomenon may be accompanied and augmented by the presence of NaCl which acts as an electrolyte in osmotic swelling processes. Two varieties of sandstone were used in the construction of the church, namely grey sandstone and brown sandstone. The latter is more porous and undergoes greater hydric expansion, showing a higher degree of deterioration. Ultrasound analysis has demonstrated that both varieties are anisotropic because they contain bedding planes and are affected by the preferred orientation of the phyllosilicates in the rock. The anisotropic nature of these stones was confirmed by capillary suction tests. The capillary front reaches a relatively low height which means that when water is absorbed, the anisotropic textural properties combined with the presence of chlorite–smectite mixed layers in the sandstone result in mechanical (shear) stress between the first few centimetres of the wet stone and the dry area behind. The latter effect favours the development of flakes, so causing the decay of the ornamental stone and the church façade.     

Characterisation and provenance of stones used in the mosaics of the domus dei Coiedii at Roman Suasa (Ancona,Italy)

The mosaics covering the floors of the rooms of the domus dei Coiedii at Suasa (Ancona, Italy) may be dated archaeologically and artistically between the late republican-Augustan age (end of the first century B.C.-beginning of first century A.D.) and the second century A.D.-first half of third century A.D. The floors were made mostly in opus tessellatum, only one in opus sectile. Tesserae used in opus tessellatum are made mainly of local stones, belonging to the so-called Umbro-Marchigiana Sedimentary Sequence: the white to pinkish and reddish tesserae consist prevalently of limestones belonging to the ‘Scaglia Rosata’ Formation (Late Turonian-Middle Eocene), and subordinately to the ‘Calcare Massiccio del Burano’, which is part of the ‘Calcare Massiccio s.l.’ Formation (Late Triassic-Early Lias). Most dark to black tesserae are composed of not fossiliferous marls and marly clays, which probably derive from the local ‘Marne a Fucoidi’ Formation; a number of them are made of very fine grained sandstones, which are found as pebbles in the alluvial sediments of the Cesano river close to Suasa, and, some, of aphyric leucite-bearing basanites from the potassic Quaternary magmatic province of central-southern Italy. Artificial glasses (red and green, rich in Pb and low in Sb; light blue, low in Pb and high in Sb), containing microliths of Pb-rich phase(s) and of wollastonite, were also used in some floors. The stones used in opus sectile are (1) sedimentary: nodular limestones belonging to the ‘Rosso Ammonitico’, which occurs in the Umbro-Marchigiana Sedimentary Succession; black marls and marly clays similar to those used in opus tessellatum; onyx marble; (2) magmatic: porphyrites (‘porfido verde antico’) and gabbros (ophite); (3) marbles: different kinds of coloured marbles, comprising ‘marmo cipollino’, ‘rosso antico’, ‘pavonazzetto’, ‘portasanta’, ‘giallo antico’, ‘bigio antico’, ‘brecce coralline’. White marbles from Marmara and Carrara were also employed.     

A multi analytical approach to discriminate the Italian colored marble “Portasanta” from Portasanta “Marmor Chium” (Greece)

The “marble” Portasanta from Caldana (Grosseto, Italy) takes its name from the strict resemblance to the ancient Marmor Chium (also this called Portasanta) coming from the island of Chios in Greece. In this work, a complete characterization of the Italian Portasanta was made: chemical (X-ray fluorescence and isotopic analyses), mineralogical (X-ray diffraction on the bulk sample and on insoluble residue after acid attack), physical (water accessible porosity and imbibition coefficients), petrographical (optical microscopy) and mechanical (compressive strength test) analyses have been carried out in order to obtain a better distinction between Italian and Greek “marble”, sometimes mistaken. The Portasanta from Caldana (Italy) was quarried surely in the sixteenth century, but a possible use of this material during Roman time is still in doubt. The study of samples from some Tuscan archaeological sites (Torraccia di Chiusi, Siena and Roselle, Grosseto) allows us to confirm the use of Portasanta from Chios for the Torraccia site and that of Caldana for Roselle.     

Investigation of Cheb relief intarsia and the study of the technological process of its production by micro computed tomography

Cheb relief intarsia is one of the most significant artistic techniques used in the early and middle baroque furniture manufacturing. The origin of this exceptional technique is closely tied to the city of Cheb and in a wider perspective, similarly to rondocubism or cubism applied in architecture; it is a branch of decorative arts distinctive just only for Czech lands. Here we report on the findings made on the basis of non-destructive X-ray micro computed tomography (μCT) analysis for determination of the condition and characteristics of the inner structures of an original plate of Cheb relief intarsia. The results of this analysis not only helped to clarify the manufacturing process itself, but also contributed to aim the future actions of the effective intarsia conservation in regard to the spreading internal cracks and defects in the plate discovered by μCT analysis.     

Nanolime suspensions applied on natural lithotypes: The influence of concentration and residual water content on carbonatation process and on treatment effectiveness

Ca(OH)2 particles with submicrometric dimensions (nanolimes) are recently introduced in cultural heritage conservation, in order to improve lime treatments. Lime nanoparticles are typically produced by a chemical precipitation process in supersaturated aqueous solutions of the reactants (calcium chloride [CaCl₂] and sodium hydroxide [NaOH]); water is then partially substituted with 2-propanol in order to improve stability and to reduce a random orientation of the particles. Aim of the present work is to analyse the influence of the nanolime suspensions concentration on the carbonatation process, in relation to the residual water content too. The obtained lime nanoparticles are characterised by X-rays diffraction (XRD) and profile analysis. Afterwards, the influence of the suspension concentration on stones protective treatments is evaluated: alcoholic nanolime suspensions, characterised by different concentration values, are applied on several natural lithotypes. Standard tests are performed to estimate the superficial consolidation and the protective treatment effectiveness: “Scotch tape test” (STT) and capillarity test. Porosimetric investigations are performed too.     

Degradation of lead-based pigments by salt solutions

Interactions of lead-based pigments with a number of inorganic salts, one of the most dangerous degradation agents of wall paintings, were studied under laboratory conditions. The results were used to interpret colour changes observed in 11th century frescoes from the church of Saint George in Kostoľany pod Tríbečom, the oldest preserved wall paintings in Slovakia. Interactions of selected pigments (lead white, massicot, red lead) with different salt solutions were performed within long-term laboratory experiments. We used a selection of naturally occurring salts (Na₂SO₄, MgSO₄, CaSO₄, NaCl, NaNO₃, Ca(NO₃)₂, Na₂CO₃, K₂CO₃ and urea) and, additionally, a range of synthetic salts that are often applied to the wall paintings during their cleaning and conservation (NaHCO₃, KHCO₃, (NH₄)₂CO₃, NH₄HCO₃). The reaction products were identified by X-ray powder diffraction. Red lead (Pb₃O₄) has a tendency to darken in all salt solutions containing dissolved atmospheric CO₂ due to disproportionation to plattnerite (PbO₂) and cerussite (PbCO₃). Massicot (PbO) in a wet state reacts with atmospheric CO₂ to form hydrocerussite and finally cerussite. Lead white (PbCO₃ and Pb₂CO₃(OH)₂) reacts with sulphates, carbonates and chlorides to form their respective salts in high yield and, sometimes, without any apparent colour change. Samples taken from the dark brown parts of the wall paintings in Saint George's church were analysed using laboratory X-ray powder microdiffraction. The presence of hydrocerussite, cerussite, plattnerite and lead magnesium carbonate was revealed. According to the results of laboratory experiments, the original lead-based pigment of the now darkened parts was red lead.     

The genesis and characterisation of ‘Marmor Misium’ from Kozak (Turkey), a granite used in antiquity

‘Marmor Misium’ was one of the most used granites of antiquity, especially for the manufacture of columns and slabs. It was quarried in the area of Kozak (Turkey) and used locally from the Late Hellenistic period and later, probably at the end of the 1st century AD, exported to Rome and other important Roman towns of the Mediterranean sea. It seems that ‘Marmor Misium’ continued to be quarried until the Early Byzantine time; it is now still quarried for local use (road paving, etc.). In spite of its historical importance and geological interest, this granite has never been the subject of detailed petrological studies. That is why in this work it has been sampled from various outcrops of the plutonite and in abandoned ancient quarries and characterised petrographically and geochemically. From the petrographic point of view, the plutonites of Kozak are medium-grained biotite-hornblende granite and granodiorite composed of 34.2–53 % (modal) zoned plagioclase, 23.7–35.4 % K-feldspar, 21.4–29 % anhedral quartz, 4.9–10 % brown biotite and 7.7 % green hornblende. These rocks are I-type metaluminous granitoids of high-k calc-alkaline orogenic series forming a crystallised body at a depth of about 10 km. The positive distinction between ‘Marmor Misium’ and two other granites used in antiquity and macroscopically very similar to it, those from the Elba and Giglio islands (Italy), is easily made by considering the absence of hornblende, the peraluminous character and the lower Sr and Ba and higher Rb contents for the latter.     

Comparison of hot-air and low-radiant pew heating systems on the distribution and transport of gaseous air pollutants in the mountain church of Rocca Pietore from artwork conservation points of view

The concentrations of CO₂, CO, formaldehyde (H₂CO) and water vapour were simultaneously monitored in various sections of a mountain church situated in the village of Rocca Pietore in the Italian Alps. The performance of a conventional, hot-air heating system and a novel design for heating the church, consisting of low-temperature heating elements, such as electrically heated pews and carpets, were compared for the supply, transport and removal of gases, the deposition and/or transformation of which may affect the preservation of displayed works of art. Experiments with sulphur hexafluoride (SF₆) tracer-gas showed a considerable influx of external air through the hot air carrier ducts of the old heating system, and also the leakage of the internal air mostly via the apertures of the doors. The ventilation rates for the total volume of the church with the hot-air heating system (on for 1.5 h), the new heating system (on for 2 h), and without heating were calculated to be 0.25, 0.18, and 0.13 h⁻¹, respectively. Without heating, a nearly homogeneous distribution of gases has been observed along both the horizontal and the vertical cross-sections of the church. Immediately after switching on the hot-air heating system, the levels of CO₂ and water vapour showed a sharp increase. After turning this system off, the levels of gases showed a slow fall and they developed a highly non-homogeneous spatial distribution indoors for many hours. In the upper region of the church, being airtight, higher concentrations of the pollutants could be detected. The low levels of CO and H₂CO, mostly originating from incense burning during services, were correlated to that of CO₂. The hot-air heating system has been proved to present a potential deterioration risk to artworks, as it increases the supply, transport and deposition probability of air pollutants. On the other hand, the novel, symmetrical heating system eliminates these undesirable effects, thus its application is advantageous to all churches involved in the preservation of works of art.     

Laser cleaning of stone artefacts: a substitute or alternative method?

Laser cleaning of ancient marble and stone monuments is nowadays a well-accepted procedure in conservation. Operators and specialists are presently divided between those giving maximum confidence to this method of cleaning and others who, in contrast, are strongly critical and emphasise possible drawbacks and damages caused by laser. As any other method of cleaning, laser also offers advantages but at the same time is limited by drawbacks. Most conveniently, it should be integrated with the other methods. On the basis of the above considerations, the authors are proposing a combined procedure using laser cleaning as a first step – in this way removing the relevant part of black gypsum encrustation – followed by chemical methods as a final step. The latter, conveniently, could be accomplished by means of anion exchange resins, better than ammonium carbonate. An experimental check-up was made of four different methods applied on three different lithotypes on the façade of the Florentine Cathedral. Laser, micro-sandblasting, ammonium carbonate and sodium EDTA were the cleaning methods compared, whilst Carrara marble, green Serpentine (Verde di Prato) and a red limestone were the three lithotypes. Results are commented by showing differences in the advantages and drawbacks among the different methods on the various lithotypes.     

The history of the “Virgin with Child” sculpture (Ottaviano,Naples, southern Italy): Hypotheses from archaeometric multi-technique investigations

A life-size whitish marble statue of a “Virgin with Child” has been recently rediscovered in the St. Rosario church located in Ottaviano, a small town near Naples (southern Italy). This artwork shows stylistic features of the Tuscan-Roman school of the 16th century, and is framed in an intriguing historical context. Historical documents testify that the sculpture was a property of the cadet branch of noble Tuscan family of the Medici, the Medici of Ottaviano. A multianalytical approach has been used to try to indicate the supply area of the white marble of the studied sculpture. Considering the whole mineralogical, petrographic and geochemical data, the source rock can be possibly limited to the main classical white marbles of the Mediterranean district, as the classical marble of Aphrodisias. A reuse practice of a former artwork can be also hypothesized.     

Trachytes employed for funerary artefacts in the Roman Colonies Regium Lepidi (Reggio Emilia) and Mutina (Modena) (Italy): provenance inferred by petrographic and chemical parameters and by magnetic susceptibility

Roman funerary artefacts belonging to the archaeological collections in Modena and Reggio Emilia, two important Roman colonies (Mutina and Regium Lepidi, respectively) in the Cispadane region (Northern Italy), are made of trachytes from the Euganean Hills, close to Padua. In particular, the petrographic and chemical parameters, besides magnetic susceptibility of archaeological trachytes, suggest Monte Oliveto as their main source; very few of them, however, come from Monte Rosso and Monte Merlo. Surprisingly the trachytes from Monselice, which were used extensively to get flagstones for paving the Roman roads of the Po plain, were not implied in funerary art. Possibly the porosity of stones was determinant in addressing the use of the Euganean trachytes: the stones from Monte Oliveto (and also from Monte Rosso and Monte Merlo), which contain frequent cavities and voids, are porous and might favour body decomposition, like important stones used in antiquity for sarcophagi (e.g. lapis sarcophagus). By contrast, the trachytes from Monselice are dense, not porous, hence harder and more resistant to abrasion, therefore suitable for flagstones.     

Effect of low and high fluence on experimentally laser-cleaned sandstone and marlstone tablets in dry and wet conditions

The eligibility of laser cleaning is tested on regionally specific sculptural stones. Marlstone and sandstone represent the most common building, architectural and sculptural stones employed in the Czech Republic since the Romanesque period. These stone types differ greatly from the marbles on which positive results have been obtained using laser cleaning. Experimental samples were prepared by sawing rock cores. Artificial blackening of samples’ surfaces simulates natural black patinas. The experimental laser cleaning was conducted using Nd:YAG commercial laser (Laserblast 50) at two different fluences—the low one corresponds to the minimum operating capability of the equipment, and the high fluence represents the maximum operating mode of the equipment (i.e. in the ordinary operating range of the equipment). The samples were cleaned under dry and wet conditions. Use of a high fluence resulted in cratering/spalling that is discussed in terms of rock mineralogical composition (presence of clay minerals), adsorption of moisture on clay minerals and physical properties (porosity). Tensional fracturing (evidenced by scanning electron microscopy) along the cleaned surface is the main mechanism of sample destruction due to the vaporization of adsorbed moisture and due to the different elasticity of present rock-forming minerals. Observed discoloration due to high fluence and insufficient cleaning effect of low fluence present other problems encountered.     

3D preserving xviii century barroque masterpiece: Challenges and results on the digital preservation of Aleijadinho's sculpture of the Prophet Joel

We present our recent efforts in the digital preservation of a set of baroque sculptures made by Antônio Francisco Lisboa, known as O. Aleijadinho, which is an important American baroque artist. The set was made in the beginning of the xix century and is composed of 12 near real sized sculptures, hand-carved in soapstone. These sculptures represent 12 of the 16 prophets from the Holy Bible and are part of a UNESCO World Heritage Site. Our group has been collaborating with UNESCO in a project that aims to preserve all these statues. We hereby present our initial efforts, consisting of the 3D digital preservation of the Prophet Joel sculpture. We developed a complete 3D digital preservation pipeline composed of four main stages: data acquisition, 3D reconstruction, texture generation and 3D model visualization. By evaluating our results in this first sculpture, we discuss the improvements we conceived before applying our pipeline in the remaining ones. Finally, we present the 3D model of the Prophet which registers the sculpture's current state and will be used in restoration, research and educational activities. We believe this contribution may be useful to guide further research on similar scenarios, showing how to avoid some practical mistakes and achieve good results.     

Insight into the conservation problems of the stone building “Bab Agnaou”, a XII cent. monumental gate in Marrakech (Morocco)

Bab Agnaou is one of the most beautiful gates of the 12th century town walls of Marrakech (Morocco). It is faced with poorly preserved stone, which has recently been subjected to preliminary laboratory studies for the purpose of collecting data useful for its restoration. The results of such studies indicate the presence of two macroscopically similar grey stones, classified as slates, which were probably sourced from quarries situated not far from the city of Marrakech. The schistosity of such stones, namely their laminated fabric, has much influenced the morphology of deterioration. The causes and mechanisms of decay have been investigated and connected to the presence of soluble salts, mainly chlorides and sulphates deriving from the mortar used to fix the stone blocks to the wall, and to local air pollution. Their concentration in the bottom 3 m of the gate due to rising damp has produced strong exfoliation and flaking phenomena through rapidly repeating crystallization/dissolution cycles. A minor contribution to the overall deterioration is due to hydrolytic phenomena partly responsible for the formation of natural brown patinas on the stone surface. Another brown patina formed of Ca-oxalates and with residual proteinaceous matter was also detected and is probably due to partly mineralized protection-treatments made with natural products such as animal glue. General indications for the restoration of the gate, based on these results, are proposed.     

An advanced church heating system favourable to artworks: A contribution to European standardisation

The European project Friendly-Heating (FH): comfortable to people and compatible with conservation of artworks preserved in churches addressed the problems caused by the continuous or intermittent heating of historic churches, which disturbs the microclimatic conditions to which the building and the artworks preserved inside have acclimatised. As thermal comfort and the preservation of artworks often conflict with each other, a balance between the two needs is necessary. The proposed heating strategy is to provide a small amount of heat directly to people in the pew area while leaving the conditions in the church, as a whole, undisturbed. This novel heating system is based on some low-temperature radiant emitters mounted in a pew to provide a desirable distribution of heat to the feet, legs and hands of people occupying it. Due to little heat dispersion, this novel system not only significantly reduces the risk of mechanical stress in wooden artworks and panel or canvas paintings, fresco soiling and cyclic dissolution-recrystallization of soluble salts in the masonry, but is energy-efficient. The detailed environmental monitoring was conducted in the church of Santa Maria Maddalena in Rocca Pietore, Italy over a 3-year period to verify the performance of the novel heating system in comparison to the warm-air system that was active earlier in the church. The methodology and results of this comprehensive and multidisciplinary study were included in three draft standards of the European Committee for Standardisation intended for use in the study and control of environments of cultural heritage objects.     

Consolidation of stone blocks prior to placement: A case study of the Roman wall in Tarragona (Spain): Report and methodology

The possible pre-consolidation of the stones used to repair the Roman wall of Tarragona was studied, on the premise that this had been carried out prior to placement in the wall. A detailed study of the stones was conducted in order to determine whether they had been treated, and if so, how this had been done. A semi-quantitative X-ray mineralogical analysis using the Rietveld method was performed, together with porosity and textural analyses. This paper concludes with a discussion of how the stones studied here were pre-consolidated using lime slurry.     

Building stone and related weathering in the architecture of the ancient city of Naples

The survey of materials constituting the buildings of the ancient city centre of Naples and of their decay typologies was carried out. Reports were entered in a database which enabled us to draw two thematic maps in a digital format: one of materials and lithotypes, and one showing weathering. On this basis, quantitative evaluations of the lithotypes were carried out. The research pointed out that the use of different lithotypes was mainly as a result of their availability and/or ease of exploitation. Furthermore, the importance of the preservation of the quarrying sites was stressed, both for their historical and cultural interest and, above all, for possible forthcoming provisioning finalized to restorations. The analysis of the results, made on a geo-mineralogical basis, as well as the thematic maps, gives a basic tool which will be very useful to those professionals involved in preservation of cultural heritage.