Article

1 H NMR depth profiles combined with portable and micro-analytical techniques for evaluating cleaning methods and identifying original, non-original, and degraded materials of a 16th century Italian wall painting

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Abstract

In this study, portable NMR was applied to monitor and evaluate cleaning treatments on the surface of a 16th century Italian wall painting. Due to the complexity of the state of degradation of the wall painting, a campaign of measurements was carried in situ to evaluate the performance of traditional and innovative eco-friendly cleaning systems such as sulphate-reducing bacteria D. vulgaris confined in hydrogels, and to compare two different cleaning systems used to remove a degraded hydrophobic organic layer. Specifically, NMR stratigraphy allowed to determine the thickness of the organic layer covering the surface of the wall painting, its distribution in the wall painting, the presence of residues after applying the cleaning treatment, and to evaluate and compare the effectiveness of applied treatments. A new analytical parameter here named the solubilization degree of the cleaning system permitted the selection of the most performing treatment. 1H NMR depth profiles allowed to evaluate changes in the permeability of the wall painting caused by the presence of organic substances during the application of water-based cleaning systems, and to evaluate the water content and its depth of penetration in the wall painting. Changes in permeability were estimated calculating another new analytical parameter, i.e. the percentage of water saturation before and after the application of the cleaning treatment. Depth profiles also permitted the evaluation of the degree of wettability of the wall painting surface as a function of the time of application, and the obtainment of a detailed information about the interaction between water molecules, the gel network and the surface of the wall painting. Finally, to obtain the chemical characterization of the artefact surface a multi analytical approach was applied using both portable and micro-invasive analytical methodologies.

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... G. Brunetti, Laura Cartechini, Patrizia Moretti, Francesca Rosi, Magdalena Iwanicka, Constanza Miliani measurements of 1 H density profiles and transversal relaxation times, T 2eff , for binders have been proved useful in taking decisions about conservation treatments. Examples include the removal of a thick, altered overpaint (150-200 mm) covering the original acrylic paint in a contemporary art installation by Louise Nevelson, in Saint Peter's Church, New York (Kehlet et al., 2018) and the monitoring of the removal of a protective wax layer, of around 400 mm, in a Renaissance mural painting by Antonio da Viterbo in the Cathedral of Tarquinia (Di Tullio et al., 2018). The main aim of the conservation work on the Renaissance mural painting was to compare the action of a microemulsion and a solvent-gel system in removing the wax layer, likely applied in a past undocumented treatment. ...
... Measurements of 1 H NMR depth profiles, recorded before and after the application of the two different cleaning systems, showed a clear reduction of the wax layer in both cases, with an evident more pronounced removal by the microemulsion. From the profiles, it was possible to quantify a reduction of 92% of the wax thickness, after 1 hour of applying the microemulsion, while after the corresponding solvent-gel application, the reduction was found to be only of 17% (Di Tullio et al., 2018). The integrative use of reflection FTIR spectroscopy confirmed a higher decrease of the wax band-intensities produced by the microemulsion, compared to the solvent-gel. ...
... Sin embargo, a pesar de esta limitación, las mediciones de los perfiles de densidad de 1 H y los tiempos de relajación transversal, T 2eff , para aglutinantes han demostrado ser útiles en la toma de decisiones de tratamientos de conservación. Los ejemplos incluyen la eliminación de una pintura gruesa y alterada (150-200 mm) que cubre la pintura acrílica original en una instalación de arte contemporáneo de Louise Nevelson, en la Iglesia de San Pedro, Nueva York (Kehlet et al., 2018) y la monitorización de la eliminación de una capa protectora de cera, de unos 400 mm, en un mural renacentista de Antonio da Viterbo en la Catedral de Tarquinia (Di Tullio et al., 2018). El objetivo principal del trabajo de conservación de la pintura mural del Renacimiento fue comparar la acción de una microemulsión y un sistema de gel disolvente para eliminar la capa de cera, probablemente aplicada en un tratamiento anterior sin documentar. ...
... 106 The effect of cleaning treatments on wall paintings has also been addressed by NMR studies. 107 The study evaluated the degradation of a 16th century wall painting in the Tarquinia cathedral in Rome, Italy. Understanding the constituent components, the current level of degradation, and the effects of previous restoration treatments were all necessary to provide the best treatment for the samples. ...
... Carbogel was found to be the better support for this purpose; however, the presence of hydrophobic beeswax impeded water uptake at the wall for both gels. 107 Another study 108 looked at a series of thickened or gelled cleaning methods for acrylic paint films containing titanium white or Hansa yellow (organic) pigments. Unilateral NMR techniques, spatial resolved profiles of the T 2eff and relative volume of water in the top layer or paint film, were used to monitor the rate of diffusion and penetration depth of water in the samples, as well as quantitatively determine the amount of water which had swelled the paint during treatment, gel vs. swab method. ...
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Nuclear magnetic resonance spectroscopy has advanced our understanding of cultural heritage objects. Solution NMR, solid state NMR, unilateral NMR, magnetic resonance imaging (MRI) and other MR techniques have been used on a wide variety of materials such as stone, ceramics, paintings, biological remains, paper, wood, textiles, resins, gums, and synthetic materials. This review highlights NMR studies that provide structural and chemical identification, moisture content and distribution, uncovers artistic techniques, determines geographical origins, identifies constituent materials of an object and helps to determine the best cleaning or treatment method for conservation. In addition, physical and chemical transformations and structural modifications due to deterioration of an object can be monitored by NMR methods, and this information provides conservators with clues as to the most appropriate methods of preservation of a unique artifact. With the continued development of NMR pulse sequences, probes and sensors, the sensitivity and utility of NMR spectroscopy in cultural heritage continues to grow.
... However, organic binders have habitually used also in wall paintings by the artists to provide protective layers or varnishes and as final touches. Furthermore, the presence of organic compounds used in past restoration works can equally be found [1][2][3]. ...
... By 1 H NMR depth profiles, the thickness of the painted layers and its variability on the whole area of the painting can be evaluated during the cleaning treatment [15]. It is equally possible to study the diffusivity of solvents and water-based cleaning system, and the thickness of residual layers which were poorly solubilized by the cleaning formulation [3]. an NMR depth profile can detect, non-invasively and in situ, the multi-layered structure of a painting. ...
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The external walls of the Cathedral of Florence are made of green serpentine, red marlstone and Carrara white marble, and intensive air pollution attack has led to their weathering, which caused black crust formation. A study was performed to evaluate the most appropriate cleaning treatment for black crust removal, adopting chemical (ammonium carbonate poultice), laser (1064 nm, Nd:YAG laser), and microbial (poultice embedding sulfate-reducing bacteria) cleaning. The effects of the different procedures on the original surfaces were evaluated by scanning electron microscopy coupled with energy dispersive X-ray (SEM/EDS) spectroscopy, Fourier transform infrared (FTIR) spectroscopy, and color measurements. One year later further color measurements were made. It was found that chemical cleaning led to non-homogeneous crust removal and that for the extremely powdery and incoherent red substratum the preferred treatment was laser cleaning. Overall, the most satisfactory treatment was the microbial cleaning process. It was the most controllable process and the most efficient for sulfate removal. Its main drawback appears to be the time needed to remove thick black crusts since numerous applications were necessary.Highlights► Comparative studies of three different cleaning procedures for black crust removal. ► Biocleaning is compared with laser treatment and performed on colored stones. ► The chemical cleaning led to non-homogeneous crust removal. ► Laser cleaning is preferred on the extremely powdery and incoherent red substratum. ► Biocleaning is the most controllable and efficient process for sulfate removal.
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A pulsed low-resolution 1H NMR relaxation study at 75 MHz was performed on chitosan and on two lightly cross-linked chitosan networks with a different degree of cross-link and different amount of added water. The spin−lattice relaxation time T1, the spin−spin relaxation time T2, and the free induction decay (FID) were measured in the 200−320 K temperature range. An aperiodic saturation recovery sequence was applied for measuring T1, while a CPMG sequence was used for measuring T2. A full deconvolution of FIDs allows a plethora of information. Lightly cross-linked chitosan chains form super adsorbing hydrogels. The amount of water in these gels at the swelling equilibrium is so high to hide completely the properties of bound water. Thus, dried samples of chitosan and of cross-linked chitosan derivatives were partially rehydrated and studied as a function of added water and of temperature. Data obtained from a 1H NMR relaxation study allowed us to measure the number of water molecules in different shells of solvation of macromolecules. Only about four water molecules per repeat unit are tightly coordinated by chitosan while the number of water molecules tightly coordinated markedly increases for cross-linked chitosans and is correlated with the maximum swelling properties of the networks.
Article
 This paper analyzes – chemically, mineralogically, and petrolographically – the patinas developed on several Mediterranean monuments made with different stones (siliceous and carbonatic) in order to establish their origin and their evolution under the present environmental conditions, and to evaluate the environmental parameters controling their development. Most of the patinas show a common sequence of layers, which, from the outer to the inner zone, are: (1) present bioactivity and/or biological remains, (2) gypsum-rich patina, and (3) calcitic brown to orange patina. Each one may exhibit different fabrics (from micritic to stromatolitic) and may be more or less continuous and homogeneous. The main mineral components are calcite and gypsum, but Ca-oxalates and Ca-phosphates have also been found associated to biological structures, as well as quartz and clays. The different fabrics and textures have been interpreted as consequence of changes in the environmental conditions which seem to be related to the biological activity, facilitating the growth of different organisms and leading to the development of a deposit with distinct characteristics (fabric, texture, porosity, etc.). The gypsum-rich patina has been interpreted as a sulphation of the underlying calcitic layer by the action of atmospheric pollutants or as dry or wet deposition from the atmospheric dust. The mineralogy and texture of the patina is independent of the nature of the underlying rock and only in few cases a micritization process has been observed as interaction between patina and rock. Recently, the penetration of endolithic microflora produced drillings and the development of a fissuration system parallel to the surface, and thus the detachment of the crust from the rock and even flackening of the rock itself has been observed. Consequently, under the present climatic conditions in the Mediterranean basin, erosion is a more active process than deposition, and the crusts and patinas show a tendency to disappear from the surface of the monuments.
Article
Many applications of various nuclear magnetic resonance (NMR) methods to characterize and monitor Cultural Heritage were reported. NMR is a very powerful tool in the chemical characterization of materials which allows light to be shed on the techniques used by artists, and can provide knowledge about the materials constituting artifacts. Knowledge of the causes of degradation of artifacts may also be achieved by NMR through the study of the chemical-physical transformation and structural modifications caused by ageing. NMR investigations may also help in planning proper restoration works. The reported investigations on archaeological bones, mummies, amber, and the identification of residues in archaeological findings, clearly show how NMR can also play an important role in a specific field of Cultural Heritage known as archaeometry which concerns the application of scientific techniques to the analysis of archaeological materials.
Article
It is shown that transverse relaxation measurements obtained from CPMG echo trains are valid even in the presence of strong, static magnetic field gradients. In the context of in situ measurements for water or oil exploration, low magnetic fields and short echo spacings are utilized to minimize diffusional effects. Under these conditions, it is shown that, for T1 = T2, the inverse Laplace transformation of the echo train is essentially independent of field homogeneity. For T1 ≠ T2, the error in determining T2 does not exceed ∼12%, even for high T1/T2 ratios. In most porous media, T1/T2 is less than 3, in which case the error is below 8%. Analytical expressions for the echo amplitudes including relaxation are derived based on the density-matrix formalism. We define recursion relations that give the density matrix at echo i by a simple multiplication of the density matrix at echo i − 1 with a set of operators describing the evolution between consecutive echoes. The echo intensity is shown to be a function of the ratio between the radiofrequency strength and the receiver bandwidth. The optimal signal-to-noise ratio is obtained when this ratio is unity. The paper provides the theoretical framework for interpreting data obtained in situ by a modern NMR logging instrument. Furthermore, the results are directly applicable to magnetic resonance imaging.
Article
This study describes an analytical approach for the characterization and origin of the encrustation formed on the surface of monuments from the Acropolis in Athens. The morphology of encrustation was investigated by optical and scanning electronic microscopy. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), energy-dispersive X-ray fluorescence (EDXRF) and scanning electron microscopy coupled with energy-dispersive X-ray analysis (SEM-EDS) identify and quantify the key elements and compounds associated with the genesis of encrustation. Black crusts (>200 μm thick), consisting of gypsum, calcite and elements such as Si, Al, Fe, Pb, Ti, Zn and Mn, were being formed from interaction between the marble surface and atmospheric pollutants. Orange-brown accretions on the Parthenon, called patinas (∼150 μm thick), comprise calcite, calcium oxalates, low amount of S, and both in the inner and outer parts significant and almost constant amounts of Si, P and Fe; P and Fe identified as hydroxyapatite and hematite, respectively. In the Parthenon patinas, the EDS distribution maps of Si, Fe and P indicate an origin that may be attributed to the residue and transformation of ancient treatments rich in these elements. Patinas from the Erechtheum (∼100 μm thick) resemble plasters consisting of calcite, siliceous sand, hydroxyapatite, calcium oxalates and hematite. EDXRF highlighted the presence of Pb in the patinas from the Erechtheum; FTIR revealed that Pb is in the form of cerussite most probably from the use of attic ochre. The patinas from the Parthenon and Erechtheum, as opposed to black crusts, are associated with the best-preserved surfaces and should remain intact during conservation interventions.
Article
Nuclear magnetic resonance (NMR) has many applications in science, medicine, and technology. Conventional instrumentation is large and expensive, however, because superconducting magnets offer maximum sensitivity. Yet NMR devices can also be small and inexpensive if permanent magnets are used, and samples need not be placed within the magnet but can be examined externally in the stray magnetic field. Mobile stray-field NMR is a method of growing interest for nondestructive testing of a diverse range of materials and processes. A well-known stray-field sensor is the commercially available NMR-MOUSE, which is small and can readily be carried to an object to be studied.
Article
In conventional NMR, samples from works of art in sizes above those considered acceptable in the field of art conservation would have to be removed to place them into the bore of large superconducting magnets. The portable permanent-magnet-based systems, by contrast, can be used in situ to study works of art, in a noninvasive manner. One of these portable NMR systems, NMR-MOUSE®, measures the information contained in one pixel in an NMR image from a region of about 1 cm2, which can be as thin as 2–3 µm. With such a high depth resolution, profiles through the structures of art objects can be measured to characterize the materials, the artists’ techniques, and the deterioration processes. A novel application of the technique to study a deterioration process and to follow up a conservation treatment is presented in which micrometer-thick oil stains on paper are differentiated and characterized. In this example, the spin–spin relaxation T 2 of the stain is correlated to the iodine number and to the degree of cross-linking of the oil, parameters that are crucial in choosing an appropriate conservation treatment to remove them. It is also shown that the variation of T 2 over the course of treatments with organic solvents can be used to monitor the progress of the conservation interventions. It is expected that unilateral NMR in combination with multivariate data analysis will fill a gap within the set of high-spatial-resolution techniques currently available for the noninvasive analysis of materials in works of art, where procedures to study the inorganic components are currently far more developed than those suitable for the study of the organic components.
Article
A new approach was explored to purify proteins in a multi-step procedure for the characterisation of proteinaceous materials (casein, animal glue, and egg) in artwork samples by gas chromatography-mass spectrometry. High concentrations of inorganic salts, such as azurite, have been found to impair the determination of protein via amino acid analysis. The effect of varying concentrations of copper-based pigments on the quantification of amino acids was evaluated through the analysis of replica paintings prepared with the three types of proteinaceous materials. Glycine, aspartic and glutamic acids are the amino acids most affected by the presence of copper salts. In the case of high concentration of salts, this interference hampers the correct identification of the proteins. To eliminate the inorganic salts, a C18 pipette tip was used to clean-up the ammonia extracts before the acidic hydrolysis step. The clean-up procedure allows us to prevent the influence of the inorganic salts and thus allows correct protein identification, though the quantitative recovery of proteinaceous material is quite low. The effectiveness of the optimised procedure was evaluated by analysing samples from two Italian wall paintings from the 13th and the 14th centuries. Without the clean-up it would not have been possible to detect the presence of a mixture of egg and animal glue in one case, and that of egg in the other one.
Article
The spin dynamics for Carr-Purcell-Meiboom-Gill-like sequences is analyzed in grossly inhomogeneous B(0) and B(1) fields. This problem is important for many applications, especially when the bandwidth of the signal is excitation limited. Examples include stray-field NMR or inside-out NMR probes used in well logging. The amplitudes of the first few echoes exhibit a characteristic transient behavior but quickly approach a smooth asymptotic behavior. For simple Hamiltonians without scalar or dipolar couplings, the evolution of a refocusing subcycle for a given isochromat is described by a rotation. Simple expressions for the signal of the Nth echo are derived in terms of these effective rotations that have a simple geometrical interpretation. It is shown that the asymptotic behavior is controlled by the direction of the axis of these effective rotations and the signal is dominated by magnetization "spin-locked" to the rotation axis. The phase of the signal is independent of the details of the field inhomogeneities. Relaxation in inhomogeneous fields leads to a signal decay that is in general nonexponential with an initial decay rate that is a weighted sum of T(-1)(1) and T(-1)(2). At long times, the echo amplitudes decay to a finite value. Phase cycling eliminates this offset. The effect of diffusion is also studied. This analysis has been applied to an inside-out NMR well logging apparatus. Good quantitative agreement is found between measurements and calculations that are based on the measured B(0) and B(1) field maps.
Article
We demonstrate the quantitative extraction of multidimensional distribution functions in the presence of grossly inhomogeneous fields. Examples are shown for diffusion-T(2) distribution functions and T(1)-T(2) distribution functions. The pulse sequences consist of an initial editing sequence followed by a long series of nominal 180 degrees pulses. They are designed such that the kernels describing the relationships between the distribution functions and the measured data are separable. The required phase cycling is discussed. We analyze in detail the extra spin dynamics effects due to the strong field inhomogeneities including the effects on diffusion and relaxation. A recently developed algorithm is used to invert the data and extract stable multidimensional distribution functions in an efficient manner. We present examples for several applications of this new technique. Diffusion-relaxation distribution functions can be used for fluid identification and for the characterization of pore geometry of porous media based on the effects of restricted diffusion. We have also determined T(1)-T(2) distribution functions of water saturated sedimentary rock and find excellent agreement with previous measurements performed in homogeneous fields.
Article
A single-sided NMR sensor to produce depth profiles with microscopic spatial resolution is presented. It uses a novel permanent magnet geometry that generates a highly flat sensitive volume parallel to the scanner surface. By repositioning the sensitive slice across the object one-dimensional profiles of the sample structure can be produced with a space resolution better than 5 microm. The open geometry of the sensor results in a powerful testing tool to characterize arbitrarily sized objects in a non-destructive way.
Article
A simple and fast method of measuring self-diffusion coefficients of protonated systems with a mobile single-sided NMR sensor is discussed. The NMR sensor uses a magnet geometry that generates a highly flat sensitive volume where a strong and highly uniform static magnetic field gradient is defined. Self-diffusion coefficients were measured by Hahn- and stimulated echoes detected in the presence of the uniform magnetic field gradient of the static field. To improve the sensitivity of these experiments, a Carr-Purcell-Meiboom-Gill pulse sequence was applied after the main diffusion-encoding period. By adding the echo train the experimental time was strongly shortened, allowing the measurement of complete diffusion curves in less than 1min. This method has been tested by measuring the self-diffusion coefficients D of various organic solvents and poly(dimethylsiloxane) samples with different molar masses. Diffusion coefficients were also measured for n-hexane absorbed at saturation in natural rubber with different cross-link densities. The results show a dependence on the concentration that is in good agreement with the theoretical prediction. Moreover, the stimulated-echo sequence was successfully used to measure the diffusion coefficient as a function of the evolution time in systems with restricted diffusion. This type of experiment proves the pore geometry and gives access to the surface-to-volume ratio. It was applied to measure the diffusion of water in sandstones and sheep Achilles tendon. Thanks to the strong static gradient G(0), all diffusion coefficients could be measured without having to account for relaxation during the pulse sequence.
Surface cleaning and conservation, Conservation 15:3, The Getty Conservation Institute
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P. Baglioni, N. Bonelli, D. Chelazzi, A. Chavelier, L. Dei, J. Domengues, E. Fratini, R. Giorgi, M. Martin, Organogel formulations for the cleaning of easel paintings, Appl. Phys. A Mater. Sci. Process. 121 (2015) 857-868.
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Physicochemical and structural characterization of Sweitenia mycrophylla gum
  • Adeyanju
Surface cleaning and conservation
  • Koller