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Characterisation of metal carboxylates by Raman and infrared spectroscopy in works of art
Abstract
This work introduces the complementary use of μ-Raman and μ-Fourier transform infrared (IR) spectroscopy for the detection of specific carbon chains and cations for the identification of metal carboxylates within oil paint microsamples. Metal carboxylates (metal soaps) form naturally when free fatty acids react with metal cations and may also be found as additives or degradation products. Twenty-two metal carboxylates were synthesised, and their spectra assembled in a reference database. Metal salts of cations commonly present in oil paintings were used, including lead, zinc, calcium, cadmium, copper and manganese. The fatty acids selected were the saturated acids palmitic (C16 : 0) and stearic (C18 : 0) and the polyunsaturated oleic acid (C18 : 1). Azelaic acid (C9 diacid), a product resulting from autoxidation of polyunsaturated acids, was also included. Metal carboxylates were characterised by Raman and IR spectroscopy, and their structures were confirmed by X-ray diffraction. Raman and IR spectroscopy proved to be complementary techniques for a full identification of the metal carboxylates in complex aged paint. Raman enables the differentiation of the carbon chain length in the C–C stretching region (1120–1040 cm�-1), and IR distinguishes the metal cation in the COO-� stretching absorption region (1650–1380 cm�-1). Principal component analysis was applied to the spectra in order to facilitate a fast and accurate method to discriminate between the different metal carboxylates and to aide in their identification. Finally, spectra from case studies were successfully projected in the principal component analysis models built, enabling a higher confidence level for the identification of copper palmitate and copper azelate in two 19th-century Portuguese oil paintings.
... Metal carboxylates were synthesised by a precipitation process involving metal salts and fatty acids, following procedures that are described in detail in other publications [17,[42][43][44]. Materials were of analytical grade and obtained from Sigma-Aldrich ® . ...
... The FTIR analyses confirmed that the precipitation process from metal salts and fatty acids produced oleates and stearates of zinc, calcium, lead and copper, in correlation with reference spectra found in literature [43,44]. After precipitation, the infrared bands corresponding to C=O stretch of the fatty acids (around 1700 cm −1 ) disappeared, being replaced by the characteristic bands attributed to COO − symmetric and asymmetric stretch of each metal carboxylate between 1600 cm −1 and 1400 cm −1 [43,44] (Fig. 6). ...
... The FTIR analyses confirmed that the precipitation process from metal salts and fatty acids produced oleates and stearates of zinc, calcium, lead and copper, in correlation with reference spectra found in literature [43,44]. After precipitation, the infrared bands corresponding to C=O stretch of the fatty acids (around 1700 cm −1 ) disappeared, being replaced by the characteristic bands attributed to COO − symmetric and asymmetric stretch of each metal carboxylate between 1600 cm −1 and 1400 cm −1 [43,44] (Fig. 6). ...
The recent multi-analytical study carried out on the Van Eyck’s Ghent Altarpiece showed the simultaneous presence of several kinds of metal carboxylates in oil-rich glaze layers. This outcome raised the question whether these carboxylates had already formed during the preparation of the oil binder by the artists. In the case of early-stage formation, they may have had an impact on the drying rate of the resulting oil, as well as on its handling properties. This hypothesis was investigated using a model system of in-house-prepared linseed oil containing incremental concentrations (2–5–10 wt.%) of relevant metal carboxylates (i.e. Ca-, Zn-, Cu-, and Pb oleates and stearates). This paper describes the influence of these type of molecules on the drying rate of linseed oil and, to an extent, on its viscosity. The drying time of the linseed oil, to which one or more metal carboxylates were added, was measured with a drying recorder while the viscosity was assessed with a rheometer. When introduced together, some of these metal carboxylates act in synergy to shorten the drying time with respect to the situation when the same metal carboxylates were added separately to linseed oil. Mixtures of Ca- and Zn-oleates proved to have a larger effect than other binary combinations. Addition of two metal oleates (combination of Ca/Zn/Cu/Pb) reduced the drying time even more. On the other hand, specific combinations of three metal stearates and/or oleates also demonstrated a significant synergistic effect towards increasing the viscosity of the binder. Especially combinations of Ca/Zn/Cu and Ca/Zn/Pb stearates and oleates gave rise to the highest level of linseed oil viscosity increase, when compared to the situation in which the same metal carboxylates were added separately.
... Additionally, Table 2 www.nature.com/scientificreports/ them [27][28][29][30][31][32][33][34][35] . The presented spectra of modified soaps distinctly show the spectral backbone characteristic of these substances. ...
... Despite the identical principal structure of the soap-forming molecule across all the samples, differences are mainly due to the added pomace, and the resulting molecular interaction and arrangement in the presence of the said admixture. The available literature on this subject attempts to accurately assign the vibrations of specific functional groups to bands in similar materials, obtained through various methods 27,29 . However, it is quite difficult to interpret and assign bands to a particular functional group due to the variety of additives used and the specific modifications to a given product. ...
... Furthermore, we observed a characteristic -C-H stretching vibrations (likely from different cis-and trans-transformations) with the maxima peaks at ~ 3010 cm −1 , 2955 cm −1 , 2917 cm −1 , and 2845 cm −1 (Figs. 6 and 7). These vibrations stem from the groups in the long hydrocarbon chain molecules in the fat fraction of the studied samples 27,29,32 . In such samples, vibrations are usually prominent due to the large number of these groups in the hydrophobic part of the molecules 29 . ...
The present study investigated several properties such as friction, hardness, penetration work, and cutting forces in soaps formulated with apple and carrot pomace at varying concentrations of 5%, 10%, and 15%. To gain insights into the molecular-level alterations within the formulated soap samples, they were spectroscopically analyzed using Fourier-transform infrared spectroscopy. The sliding friction analyses revealed that the investigated extrudate additives had no significant impact on the frictional forces of the soaps. However, notable differences were observed in the cutting force, hardness, and penetration work between the control and pomace-added samples. Excluding the control samples, no statistically significant distinctions were found between the cutting force, hardness, and work of penetration of soaps containing apple pomace and carrot pomace. Moreover, the quantity of pomace incorporated did not induce any significant variations in the results. The obtained samples were characterised at the molecular level using FTIR Fourier transform infrared spectroscopy. On the other hand, alterations in band intensities suggested improved molecular packing of the compounds within the samples due to the presence of the additives.
... Overall, the spectral profile of Raman spectra of soaps is quite similar with respect to the unprotonated fatty acids, as reported elsewhere. 15,34 This evidence is related to the dominating presence of unprotonated fatty acids both in the fresh fatty acids and in the soaps. 5 However, several additional bands arise below 1200 cm −1 that cannot be ascribed either to a trace of copper sulfate used for soap preparation ( Figure S7) or to the polymerization of unreacted carboxylic acids, according to unvaried intensity of cis-olefin-related modes (see Figure S8). ...
... 35,36 In particular, the latter peak is found to characterize Cu(II)-oleate in other vibrational studies of soaps. 2,34 In previous studies, it was shown that copper soaps tend to aggregate to form ordered phases: e.g., in the copper oleate case (sample SOL, Figure 9), the three peaks at 920, 886, and 865 cm −1 we observed in the spectrum of SOL, which are barely visible in the spectrum of FOL, were assigned respectively to ν CC of C α and ϱ CHd 2 in literature and were found to increase their intensity in copper-oleate soaps. 35,36 Analogously, the copper linoleate spectrum of Figure 10 is characterized, in this spectral region, by an increased intensity in 917, 880, and 842 cm −1 peaks with respect to the neutral fatty acid: this piece of evidence can be as well attributed to copper soaps in a more ordered phase, as reported by others, when linoleic acid interacts with Cu(II). ...
... Also, the three peaks at 599, 610, and 625 cm −1 in the SLIL spectrum (Figure 10), at a slightly lower frequency than expected for a "free" carboxylate deformation, can be assigned to deformation of COO coordinated to the Cu(II) ion, according to the literature. 34 The several medium-intensity peaks below 500 cm −1 of SOL and SLIL spectra can be assigned to Cu−O stretching as suggested elsewhere. 15,38 On the opposite, the spectrum of copper linolenate (SLIN), reported in Figure 11, shows almost exclusively the signal of neutral carboxylic acid and no significant variation below 800 cm −1 . ...
... Figure 3a shows representative FTIR spectra of samples 06, 08, and 11. The composition of the deposits and patina detected by ATR-FTIR and XRPD analyses is summarized in Table 2, while the main FTIR vibrational bands of the detected compounds and their assignments are listed in Table S2 [35][36][37][38][39][40][41][42][43][44][45][46][47][48]. The XRPD patterns are shown in Figure S2. ...
... ATR-FTIR analysis of small fragments of gilding (sample 08, Figure 3a) showed the presence of a lipid compatible with an oil binder, as well as moolooite and gypsum (see Table S2 for vibration band assignments). MicroATR-FTIR analysis of the layer visible under the gold further revealed vibrational bands associated with ester-type substances: νas(CH3) and νs(CH2) at 2928 and 2858 cm −1 , respectively; ν(C=O) at 1710 cm −1 , and antisymmetric and symmetric ν(COO − ) vibrations and δ(CH2) between 1615 and 1406 cm −1 (Figure 3b), compatible with a mixture of drying oil and metal carboxylates [42][43][44]50]. ...
... The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/heritage7020047/s1, Figure S1: Sampling points and corresponding samples (powders and fragments) observed under stereomicroscope; Table S1: For each XRF point of analysis, elements detected and detail of the analyzed surface; Table S2: Main vibration bands detected in the samples taken from the eagles, with their assignments; Figure S2: XRPD patterns; Figure S3: SEM-EDS analysis of the alloy of samples 01 (body) and 02 (bale of cloth) from the Western eagle. References [35][36][37][38][39][40][41][42][43][44][45][46][47][48] Data Availability Statement: The datasets used and analyzed during the current study are available from the corresponding author upon reasonable request. ...
The gilded bronze eagles that stand upon the summit of the Tabernacle by Michelozzo in the Abbey of San Miniato al Monte, Florence (Italy) are an exquisite example of Italian Renaissance sculpture. Commissioned by Piero di Cosimo de Medici, the two eagles, representing the ancient Arte di Calimala, were cast and decorated by Maso di Bartolomeo in the 1448–1449 period. A multi-analytical approach was set up to characterize the state of conservation, materials used, and artistic technique of the eagles. Non-invasive methods were used and integrated with micro-invasive analyses, such as X-ray fluorescence (XRF) and Fourier-transform infrared (FTIR) spectroscopy, X-ray diffractometry on powders (XRPD), scanning electron microscopy coupled with EDS (SEM-EDS), and metallographic investigation. The results depict shiny-looking eagles, suggesting the use of oil gilding on almost all surfaces and revealing the presence of polychromies, which is almost unusual in XV-century bronze statuary and is initially hidden by deposits and corrosion products. Indeed, the paws were originally painted with azurite, while the use of cinnabar imparted a vivid red color to the tongue. A black paint containing mercury was found on the eyes and talons. The bales of cloth were decorated with silver, which is now almost completely lost and whose remains are not visible due to being tarnished, while fine details in gold were detected on the lanyard.
... Various types of metal carboxylates were found as highlighted by the characteristic spectral features observed in some of the registered spectra. The peak around 1516 cm −1 can be ascribed to lead soaps [56] while the peak at 1320 cm −1 is characteristic for calcium oxalates [45] that typically also display a sharp peak within the 1620-1580 cm −1 region, this last one overlapping in this case with the amide I band. Zinc carboxylates, related to the presence of a zinc based compound (possible use of zinc white), may also be present as inferred via the sharp peak at 1539 cm −1 (zinc palmitate) (Figure 7b,c) and the peak at 1454 cm −1 (zinc oleate) [56]. ...
... The peak around 1516 cm −1 can be ascribed to lead soaps [56] while the peak at 1320 cm −1 is characteristic for calcium oxalates [45] that typically also display a sharp peak within the 1620-1580 cm −1 region, this last one overlapping in this case with the amide I band. Zinc carboxylates, related to the presence of a zinc based compound (possible use of zinc white), may also be present as inferred via the sharp peak at 1539 cm −1 (zinc palmitate) (Figure 7b,c) and the peak at 1454 cm −1 (zinc oleate) [56]. Although the zinc oleate absorption at 1454 cm −1 overlaps with the C-H bend absorption given by the protein binder, the sharp peak suggests that zinc soaps are present as well. ...
... The hypothesis on the presence of a zinc-based compound is also sustained by registered XRF data that highlighted high concentration of Zn on sample S4, extracted from the dark brown background of the icon. The presence of copper soaps can also be inferred by the shoulder band observed at 1588 cm −1 [56]. ...
As part of a detailed investigation project focused on the painting materials and technical features used in Wallachia during the 17th and 18th century, the imperial icon “Mother of God with Child” from the Orthodox Church of the “Annunciation” in Râmnicu Vâlcea, Romania, was investigated before the restoration intervention. A minimally invasive multi-analytical approach consisting of high-resolution digital radiography, hyperspectral imaging, UV fluorescence imaging, portable X-ray fluorescence, and Fourier transform infrared spectroscopy was used. The results emphasized several key features, such as: the structure of the wooden panel, the nature of pigments and of the painting technique frequently used at that time, and various defects of the pictorial layer including traces of previous restoration works, most probably made at the end of the 18th century.
... Infrared spectroscopy has been highly successful in investigating metal soaps and distinguishing them from their fatty acid precursors [45][46][47]. The most important infrared feature of carboxylates is the symmetric and antisymmetric stretching vibrations of the carboxylate ion, generally occurring at 1600-1500 and 1420-1380 cm −1 . ...
... The most important infrared feature of carboxylates is the symmetric and antisymmetric stretching vibrations of the carboxylate ion, generally occurring at 1600-1500 and 1420-1380 cm −1 . The actual maxima primarily depend on the metal cations and the type of coordination, while no significant dependence of carboxylate maxima on the fatty alkyl chain lengths has been observed [11,13,[47][48][49]. ...
... Unidentate coordination assumes the highest Δ values, bridging geometries its lowest, while chelates and ionic Fig. 1 Consecutive spectra of caproic acid (C6) after deposition on copper-zinc alloy surface a full spectra; b zooming in the region 1800-1350 cm −1 from the same spectra. Ambient temperature was recorded at 23 °C and RH at 37%; time is given in hours:minutes structures (or salts) show intermediate values [47,52,53]. Besides, copper forms binuclear coordination complexes [54,55] with v as approx. ...
The reactivities of various fatty monoacids and diacids on copper metal-containing surfaces were investigated through reflection–absorption infrared spectroscopy. The formation of copper carboxylates is detected on pure copper surfaces, while copper and zinc carboxylates are simultaneously formed on brass surfaces. Following the decrease of acid carbonyl and the formation of carboxylate infrared bands, it is shown that fatty monoacids C8 and C10 react with clean/polished copper and its zinc alloy within 2–4 h, while those with chains > C12 react within days. At the end of the processes, only the corresponding metal carboxylates are detected in all cases. An explanation for the above is offered on a molecular mobility and acidity basis, where the lower monoacids (liquids in room temperature), also having lower pKa values, favor higher reaction rates. Furthermore, it is argued that longer-chain fatty monoacids, when deposited from their solutions, allow for favorable orientation resulting in self-assembled monolayer-type molecular packing on the copper surface, which may additionally rationalize the slower reaction. Interestingly, fatty diacids do not form any carboxylate products under the same conditions, as it is argued that their molecules may efficiently pack as self-assembled multilayers on copper and ultimately protect it. The possible implications of the fatty monoacid and diacid behavior on the archaeological organic residues level and regarding the stability of copper alloys are discussed.
... Infrared spectroscopy has been highly successful in investigating metal soaps and distinguishing them from their fatty acid precursors [42][43][44]. The most important infrared feature of carboxylates is the symmetric and antisymmetric stretching vibrations of the carboxylate ion, generally occurring at 1600 − 1500 and 1420 − 1380 cm − 1 . ...
... The most important infrared feature of carboxylates is the symmetric and antisymmetric stretching vibrations of the carboxylate ion, generally occurring at 1600 − 1500 and 1420 − 1380 cm − 1 . The actual maxima primarily depend on the metal cations and the type of coordination, while no signi cant dependence of carboxylate maxima on the fatty alkyl chain lengths has been observed [11,13,[44][45][46]]. ...
... An interesting vibrational feature associated with the symmetry of the metal-carboxylate coordination is the difference between the antisymmetric (v as ) and symmetric (v s ) bands (often called the 'delta', Δ), rst introduced by Deacon and Phillips [47]; the higher the coordination symmetry, the lower the distance between the antisymmetric and symmetric maxima [48,49]. Unidentate coordination assumes the highest Δ values, bridging geometries its lowest, while chelates and ionic structures (or salts) show intermediate values [44,49,50]. Besides, copper forms binuclear coordination complexes [51,52] with v as approx. ...
The reactivities of various fatty monoacids and diacids on copper metal-containing surfaces were investigated through reflection-absorption infrared spectroscopy. The formation of copper soaps is detected on pure copper surfaces, while copper and zinc soaps are simultaneously formed as mixtures on brass surfaces. Following the changes of acidic carbonyl and carboxylate infrared bands, it is shown that fatty monoacids C8, and C10 react with clean/polished copper and its zinc alloy within 2–4 hours, while those with chains > C12 react within 15–40 days. An explanation for the above results is offered on a molecular mobility basis, where liquid monoacids at room temperature favour higher reaction rates. Furthermore, it is argued that longer-chain FMAs allow for favourable orientation resulting in self-assembled monolayer (SAM)-type molecular packing on Cu surface, may explain the slower reaction. Fatty diacids, on the other hand, do not form any carboxylate products under these conditions. In light of this interesting result, it is argued that dicarboxylic acids may also pack as self-assembled layers on Cu and ultimately protect it. The implications for fatty organic remains in copper containers are discussed, with emphasis on the stability of archaeological copper metal and carboxylates serving as molecular markers for the presence of fatty monoacids as residues in archaeological containers. Besides, the utilization of fatty acids, based on the above behaviour in copper-based dosimeters, such as those used in the Oddy test, is suggested.
... The following materials were used as Raman and infrared material references: pure cellulose nitrate membranes (Amersham Protran, 0.2 µm), camphor (96 %, Sigma-Aldrich), pure microcrystalline cellulose powder (Sigma-Aldrich), pure castor oil (Soft & Co), barium sulfate (99 %, Alfa Aesar), palmitic acid (98 %, Panreac) and zinc palmitate [35]. ...
... Infrared vibration bands found in sheets 3, 5 and 6 at 1539 cm -1 The challenge of cellulose nitrate-coated fabrics: molecular characterization of celluloid detachable collars and Fabrikoid suggested the presence of metal carboxylates, namely zinc palmitate and stearate. This was confirmed by μRaman that detected peaks related to zinc carboxylates [35] (Figure 4). The list of pigments that give color to the Fabrikoid sheets is shown in Table 2. Two pigments reported in 1922 to accelerate degradation were found in Fabrikoid sheets 3, 5 and 6: Prussian Blue (Fe4[Fe(CN)6]3) and Chrome Yellow (PbCrO4). ...
In the 19th century, significant linen and leather imitation products were invented using cellulose nitrate-coated fabrics, including celluloid detachable collars and Fabrikoid artificial leather, now preserved in the Hagley Museum and Library, USA. Using optical microscopy, µRaman, and µFourier Transformed Infrared spectroscopies, this study highlights the need for characterizing the heterogeneity of these materials at the microscale. While the detachable collars have well-preserved fabric coatings composed of cellulose nitrate, camphor, anatase (TiO2), and carbon-based particles, Fabrikoid’s pigmented cellulose nitrate-castor oil systems show problems. Our molecular data align with a 1922 report on Fabrikoid degradation, revealing free fatty acids and carboxylates formed due to oil oxidation. This is concerning as these materials were used until the 1960s, demonstrated by the analysis of objects from the National Museum of Costumes in Portugal. Future studies should address the compatibility of cellulose nitrate with fatty acids and the reactivity of additives in these systems.
... The ATR-FTIR spectrum of fragment S13 ( Figure S3a) did not show the protein-related bands; on the contrary, characteristic bands ascribed to an oily binder are present at 2920, 2850, and 1418 cm À1 due to ν as CH 2 , ν s CH 2 , and δCH 2 from the aliphatic chain; 1714 and 1629 cm À1 due to νC=O from carboxyls and residual Amide I; 1557 cm À1 from residual Amide II; 1453 cm À1 due to CH bending and νC-O in carbonates; 1318 cm À1 due to νC-O (Iorio et al., 2019). More punctual analysis by ER-FTIR ( Figure S3b) suggested the presence of metal soaps aggregates (calcium stearate): bands at 1575 and 1540 cm À1 are assigned to ν as COO À whereas the band at 1465 cm À1 is related to ν s COO À (Otero et al., 2014;Vichi et al., 2018). Generally, metal soaps are degradation products in painting since they originate from the reaction between metal cations of inorganic pigments and fatty acid fractions of drying oils used as binders (Centeno & Mahon, 2019;Cotte et al., 2017;Iorio et al., 2019Iorio et al., , 2021Noble, 2005;Otero et al., 2014;Sodo et al., 2018). ...
... More punctual analysis by ER-FTIR ( Figure S3b) suggested the presence of metal soaps aggregates (calcium stearate): bands at 1575 and 1540 cm À1 are assigned to ν as COO À whereas the band at 1465 cm À1 is related to ν s COO À (Otero et al., 2014;Vichi et al., 2018). Generally, metal soaps are degradation products in painting since they originate from the reaction between metal cations of inorganic pigments and fatty acid fractions of drying oils used as binders (Centeno & Mahon, 2019;Cotte et al., 2017;Iorio et al., 2019Iorio et al., , 2021Noble, 2005;Otero et al., 2014;Sodo et al., 2018). Calcium could arise from the underlying preparatory layer. ...
A painted wooden shield from the 16th century, commonly traced back to the famous Lepanto Battle (1571), was investigated by a multi-analytical approach to identify its manufacturing process and shed light on its cultural provenance. The typology is coherent with both the Christian and Ottoman armies and does not allow for an attribution. Radiocarbon dated the shield to two time intervals (1470-1525, 1580-1625, at 68% level of probability), compatible with the date of the Battle of Lepanto. Optical and Scanning Electron Microscopy, Attenuated Total Reflectance, External Reflection Fourier Transform Infrared, micro-Raman and Energy Dispersive X-ray Spectroscopy, and histo-chemical and shrinking temperature tests were used to characterize the artefact. The shield resulted to be made of softwood panels, covered by a stratigraphy of flax fibres, cattle skin, and a painting preparation layer of hydromagnesite. Adhesion was ensured by bone glue. Oblique, red, and cinnabar stripes alternating on the white preparation are visible on the front of the shield, whereas a homogeneous dark paint covers the back. None of the raw materials was informative by themselves, but the unusual presence of the hydro-magnesite could be crossed with the geographical context , resulting in a promising outcome for future isotopic and trace element studies.
... This is the case for pigment characterization [17,18], conservation-induced weathering/degradation processes of cultural heritage [17,19], palaeontology/prehistoric art [20,21], or forensic applications and authenticity research [22,23]. However, at the same time, the use of chemometrics within these fields is rare and when it is applied, it is limited to classical mathematical approaches such as Principal Component Analysis (PCA) [22,24], hierarchical clustering [25,26], Gaussian/Lorentzian regression [27,28] or other conventional statistical tools [29]. Nevertheless, the richness of archaeological samples and our desire to delve deeper into our inquiries now necessitate the development and/or the implementation of much more advanced methods [14,30] capable of addressing the scientific issues of both communities. ...
... A normalization constraint is then used, but only for spectra. These constraints are applied in order to exclude some solutions during the MCR-ALS optimisation and thus reduce the rotational ambiguity inherent to these types of matrix decomposition calculations [24,31]. The MCR-ALS Matlab code is available free on the website: http ://www.mcrals.info/. ...
... In the µ-FTIR spectrum from Tree of Paradise, this was deduced by the presence of a sharp ν(−COO − ) asymmetric stretching modes ca. 1549 and 1530 (in addition to peaks at 1594, 1465, 1457, 1415, and 1319 cm −1 ) characteristic of crystalline zinc soaps of fatty acids, particularly zinc oleate (zinc 9-octadecenoic acid, C 36 H 66 O 4 Zn) (Fig. 17) [15,65]. The single sharp ν(−COO − ) asymmetric stretching mode observed ca. ...
... The single sharp ν(−COO − ) asymmetric stretching mode observed ca. 1539 in the spectrum from L'arbre du Paradis could be indicative of a zinc palmitate (zinc hexadecanoate) or stearate (zinc octadecanoate) [65]. However, in other spectra, a broad, rounded ν(− COO − ) peak centered ca. ...
The richly decorative and imaginative works by French artist Séraphine Louis (1864-1942) have long elicited fascination , and her working methods have often eluded art historians and conservators alike. Working in secret and outside established art circles, Séraphine employed materials such as natural resin varnishes and was said to have used household paints in addition to traditional artists' oil paints. In this study of six works in the collections of the Musée d' Art et d' Archéologie, Senlis (MAA), The Museum of Modern Art, New York (MoMA), and The Metropolitan Museum of Art, New York (MMA), attention was given to Séraphine's choice of colors and paints, in addition to identifying possible additions to or manipulations of painting media by the artist. Technical imaging was carried out using UVF to visualize the extent of Séraphine's use of natural resins. Analysis of the palette relied on XRF techniques and limited sampling for analysis by Raman and µ-FTIR spectroscopies. Overall, the following pigments were identified: lead white, zinc white, carbon-based black, red and brown ochres, umber, vermilion, alizarin lake, rhodamine B lake, Prussian blue, cobalt blue, ultramarine blue, chrome green, emerald green, viridian, cadmium yellow, and lead chromates, including chrome yellow deep and light, zinc yellow, and chrome orange. THM-Py-GCMS analysis of selected samples supported the documentary evidence of Séraphine's use of household oil paints; a single instance of a cellulose nitrate enamel paint was additionally determined by µ-FTIR. The chromatographic analysis also indicated a natural plant resin in her varnishes, probably dammar in combination with pine resin. Overall, this material investigation, accompanied by the art historical record, better reveals the techniques of an experimental painter whose works have come to epitomize French outsider artists of the early twentieth century.
... Only in one sample, GSM6 corresponding to the priming layer, cerussite (CO 3 2− asym stretch at 1438 cm −1 and 1405 cm −1 , CO 3 2− sym stretch at 1052 cm −1 , and in plane CO 3 2− bending at 680 cm −1 ) [31] and lead white (OH stretch at 3538 cm −1 , CO 3 2− asym stretch at 1397 cm −1 CO 3 2− sym stretch at 1046 cm −1 , and out-of-plane and in plane CO 3 2− bending at 840 and 683 cm −1 , respectively) [32] were detected together with esters of carboxylic acids, lead carboxylates and traces of gypsum (Figure 2a). Esters of carboxylic acids (oils) and lead carboxylates can be inferred from the signals at 2926-2929 and 2850 −2 cm −1 (CH 2 stretch), 1728 cm −1 (C=O stretch of esters of carboxylic acids) [33], and 1524 cm −1 (asym stretch of carboxylates) [34]. However, due to the non-homogeneity of the substrate and the selectivity of the sampling, the substances identified in each spectrum can be slightly different, both in composition and concentration. ...
... The green color has been identified as verdigris basic (chemical formula Cu(CH 3 )COO) 2 [Cu(OH) 2 ] 3 ·2H 2 O) for the characteristic peaks at 1568 and 1415 cm −1 (asym and sym stretch of copper carboxylate, respectively) and at 3371 cm −1 (OH stretch) [47,48]. The use of oil as a binding medium is supported by the peaks at 2926, 2855 and 1740 cm −1 , as well as by the presence of other peaks due to CO stretch of carboxylic acids (1713 cm −1 ), and COO − stretch of copper carboxylates (1586-1587 cm −1 and 1417-1421 cm −1 ), partially covered by the signals of copper acetate (verdigris basic) [34]. ...
After a huge non-invasive diagnostic campaign performed on the corpus of Giovanni Santi’s artworks, three paintings were selected and investigated: the Martyrdom of Saint Sebastian panel, the Visitation altarpiece and the canvas with Tobias and the Archangel Raphael (c. 1487 and 1494). Micro-invasive investigations including optical microscopy, ESEM-EDX, micro-Raman spectroscopy, FTIR and FTIR-ATR spectroscopy and GC-MS were carried out on selected micro samples. The results of the integrated analyses confirmed the use of a Renaissance palette with oil and, only in a few cases, tempera techniques. Some significant peculiarities emerged in Santi’s practice, as he used localized off-white priming and colorless powdered glass with a siccative oil—in red, flesh, pinkish and green hues—confirming the influence of the Flemish painters in Urbino and, possibly, also in western central Italy. This innovative technical expedient compared to the traditional Italian painting technique was identified also in red and bluish samples collected from the Communion of the Apostles panel painted by Justus of Ghent around 1473–1474 for Urbino Corpus Domini Confraternity. The Flemish master was called to the court of Duke Federico to paint in oil and his presence at the ‘Urbino workshop’ probably contributed to the diffusion of this technique. Both in Giovanni Santi’s paintings and the Communion of the Apostles, the glass particles are related to a soda-lime glass typical of the Italian area, widely detected in Italian paintings from the late 15th and 16th centuries.
... The following materials were used as Raman and infrared material references: Pure cellulose nitrate membranes (Amersham ™ Protran ® , 0.2 µm), camphor (96%, Sigma-Aldrich), zinc oxide (ZnO, Sennelier), vermilion (α-HgS, May & Baker LTD), PMMA sheet (unknown supplier), phenol-formaldehyde billiard ball (Aramith), 87% PVC-13% PVAc copolymer (Aldrich Condensed Phase library, CAS number 9003-22-9) and calcium stearate [64]. ...
... Figure S13. Infrared spectrum of a calcium stearate reference, for more details on this reference preparation and characterization please see Otero et al. (2014). Figure S14. ...
In the 1870s, dentures were one of the first products made with celluloid, the first semi-synthetic plastic. Despite the significance of denture development in the history of celluloid and plastics, the chemical characterization of dentures in museum collections has never been attempted. It is urgent to assess the extent of celluloid heritage in denture collections due to the high degradation risk that this material imposes. In this work, 21 dentures from the National Museum of American History and from the Dr. Samuel D. Harris National Museum of Dentistry were characterized using a multi-analytical methodology using handheld Raman, X-Ray fluorescence, and micro-Fourier transformed infrared spectroscopies. All dentures were successfully characterized: 12 are made of celluloid, 4 of vulcanized rubber, 2 of phenol–formaldehyde, 2 of polyvinyl chloride—polyvinyl acetate copolymer (PVC-PVAc) and 1 of polymethyl methacrylate (PMMA). The identification of the dentures’ base materials allowed a better understanding of their history and posed new questions about their conservation. Handheld Raman was demonstrated as an excellent in-situ tool for the study of polymeric materials.
... As an example, lead, calcium, and copper carboxylates from 15th century paintings were identified by ν as (CO) frequencies 1540 and 1513, 1576 and 1539, and 1585 cm −1 . Metal soap chains can also be identified by Raman spectroscopy [32]. Last, but not least, the elemental distribution of metals and the new formed metal carboxylates can be obtained by X-ray fluorescence (XRF) [33] and, respectively, by X-ray diffraction (XRD) [34,35]. ...
... According to FTIR spectra, gypsum from the painting can be identified (1627 cm −1 and 1126 cm −1 ) and the proof of its application has been shown above, by visual photo taken from the church. Quartz is generally indicated by the typical doublet at 779-800 cm −1 [32]. ...
Currently, approximately 70% of paintings in museum collections are affected by the presence of metallic soaps, evidenced by spherical globules visible on the surface of the paintings. They are responsible for altering the paintings’ surface through processes such as exfoliation and cracking, or even in the form of surface “skins” that appear in the pictorial layers. The objective of this study is the investigation of the icon paintings from Saint Mary Monastery, Techirghiol, Romania, which underwent some restoration procedures. This study is so important/significant, due to the presence of efflorescence that is correlated with the conversion of some fatty acids, as palmitic acid, stearic acid and azelaic acid, in the so-called metallic soaps through the reaction of the metals contained in the pigments from the painting layer and the binder. The investigated paintings are strongly affected by zinc carboxylate aggregation, and for this, the sample was embedded in polyester resin and the obtained cross-section, after polishing, was investigated by microscopic techniques (optical microscopy (OM), stereomicroscopy, and scanning electron microscopy with electronic dispersion spectroscopy (SEM-EDS), Fourier-transform infrared spectroscopy (FTIR), Raman spectroscopy, and gas-chromatography with mass spectrometry (GC-MS) in good agreement with data from the literature. The potential result of this study is the identification and quantification of the metallic soap generated as a white deposit (probably salts, a kind of white efflorescence), from the binding medium of the metal carboxylate ionomer, by the crystallization of saturated fatty acids, through polymerization in oil. Six pigments (calcite, lithopone, carbon black, red ochre, vermilion, and ultramarine), present in the sublayers of the samples were identified.
... The use of soap, however, is mostly dependent on empirical information, and the choice of soap for a given purpose is influenced by economic considerations. These metal soaps can be synthesized through processes like double decomposition (metathesis), direct reaction of carboxylic acid with metal oxides, hydroxides, and carbonates, or direct reaction of metals with molten fatty acid (Smith, 2019;Arend, et al., 2011;Baij, et al., 2018;Otero, et al., 2014;Hermans, et al., 2015;Meilunas, Bentsen, & Steinberg, 1990;Neonufa, et al., 2018;Margaret, et al., 2016;Dwivedi, Gangwar, & Sharma, 2014;Gupta, et al., 2012;Gabrieli, et al., 2017;Nelson, & Taylor, 2014;Singh, Poonia, & Shukla, 2024;Bhutra, Sharma, & Sharma, 2018). ...
The physicochemical properties of cobalt and praseodymium (Caprate) soaps in their solid forms using infrared (IR) spectroscopy, thermal analysis, and X-ray diffraction provide intricate insights into their molecular organization, thermal characteristics, and crystalline structures. IR analysis reveals the presence of fatty acids in a dimeric state due to hydrogen bonding, contributing to the partial ionic nature observed in the soaps. X-ray diffraction measurements confirm the double-layer structure in both cobalt and praseodymium soaps by calculating long spacings. Thermal analysis demonstrates that the decomposition reaction follows zero-order kinetics, with activation energies of 0.00 kJ/mol in both cobalt and praseodymium (Caprate). Thus, exploring the solid-state physicochemical attributes of these soaps offers valuable insights into their structural, thermal, and crystalline properties.
... Pristine particles and weathered particles exhibited similar FTIR spectra looking at the full spectrum range (Fig. 1A). However in the wavenumber range between 1000 cm −1 and 1800 cm −1 (Fig. 1B), a broadband peak around 1094 cm −1 , associated with the C-O carboxyl group can be seen for SGF-treated particles, 67 and a minor peak at 1716 cm −1 , corresponding to the CO carbonyl group can be seen for DI water-weathered and seawater-weathered particles. 68 The formation of these chemical functional groups has been frequently reported as indicative of the chemical transformations that polymers undergo during photooxidation weathering. ...
Microplastics pose a growing environmental threat with complex implications for human health. Despite the extensive research on the cytotoxicities of microplastics, gaps remain in understanding cellular responses to the interplay...
... Caratage (K) is, instead, estimated by calculating the ratio of pure gold to the total weight of the alloy, determining the percentage of gold in the gold leaf, with higher caratages indicating a higher proportion of gold over copper or silver [26,27]. Moreover, thanks to the possibility of scanning large areas with an XRF spectrometer (Macro Area XRF or MA-XRF), we can determine the foil size, which is assessed thanks to the increased thickness derived from the overlapping areas [15,[28][29][30]. ...
This study investigates the practices and rules of Genoese gilding, drawing insights from a 16th-century manuscript containing regulations for gold leaf production. Employing X-ray and ion beam techniques, we quantitatively assess the manuscript’s gold leaf thickness without destructive sampling. Artisanal goldbeater-produced leaves of different thicknesses, applied with a guazzo or mordant technique, served as standards. Further analysis of samples with unknown thickness from the furniture of Palazzo Spinola di Pellicceria in Genoa (Italy) has confirmed the method’s applicability to practical cases. External beam Rutherford backscattering spectrometry (RBS) and particle-induced X-ray emission (PIXE) analyses were carried out using 3 MeV protons at the LABEC accelerator laboratory in Florence. A linear relationship between Gold Lα peak yield and leaf thickness, as measured by RBS, has been established for optimal calibration of portable or hand-held X-Ray fluorescence (XRF) instrumentation for in situ measurements. Moreover, the caratage of the gold foil preserved in the manuscript has been assessed.
... A micro-FTIR spectrum performed on a sample taken from the dark blue layer reveals the presence of lipid content (2920, 2850, 1720, 1450 and 711 cm −1 ) [43], proteins (1650, 1550, and 1450 cm −1 ) [42], calcium oxalate (1320 cm −1 ) [44], metal-carboxylates (1570 and 1540 cm −1 , attributed to COO − stretching mode) [44,54], calcium carbonate (1406 and 870 cm −1 ) [48], and aluminosilicates (995 cm −1 attributed to the O-Si-O anti-symmetric stretching mode) [55], as depicted in Figure 8. The results suggest that the pictorial layer is composed of a lipid binder (i.e., oil) and aluminosilicates (i.e., ultramarine blue) as the pigment. ...
The removal of non-original superimposed layers covering the original pictorial layer in paintings is a common practice to restore the authentic appearance of surfaces and mitigate potential risks to artwork preservation. Contemporary assessments of the effectiveness of such cleaning treatments often employ non-destructive analytical methods. However, many existing techniques face limitations, either lacking specificity in compound identification or analyzing very limited areas (<millimeters) through a point-by-point approach. This study introduces the application of a macro Fourier transform infrared scanner, in reflection mode (MA-rFTIR), as an effective tool for supporting restorers during cleaning processes. This method proved successful in addressing challenges related to the removal of calcium oxalate films and non-original superimposed layers on two ancient paintings.
... The characteristic stretching modes of the carboxyl groups, both symmetric ν s (CO 2 ) and asymmetric ν a (CO 2 ), correspond to the frequency ranges of 1300 to 1400 cm − 1 and 1500 to 1600 cm − 1 , respectively [48]. These frequency ranges are within the broad range of 1300 to 1600 cm − 1 for the metal carboxyl stretching vibrations [49]. Fig. 7 presents the Raman and IR spectra (observed and calculated) in the range of 1200 to 1700 cm − 1 . ...
In this work, bis(L-alaninate)copper(II) crystals were obtained by the slow solvent evaporation method. X-ray diffraction patterns, Raman and infrared spectra were recorded under ambient conditions. The initial geometry of bis(L-alaninate)copper(II) was optimized and the structural properties (lengths and angles between atoms) were analyzed and discussed using Rietveld and plane-wave methods. This work perhaps is one of the first to compare the results of the geometric structure using both methods. The results obtained show a good correspondence between the two methods, despite the complexity of the system. The optimized geometric parameters were used in the Density Functional Theory calculations. The calculated spectra and obtained vibrational frequencies were compared with experimental data. The assignment of vibrational modes was made in terms of the Potential Energy Distribution technique, as well as reinforced by classifications known in the literature for similar systems.
... | Friction carboxylate salts, which are tribochemically generated [34,37,38,40]. The carboxylate-related peaks can appear at slightly different wavenumbers depending on the metal it bonds to and the bonding configuration [41][42][43][44][45]. Interestingly, carboxylates are found on the transfer film from all environments, even though both oxygen and water are necessary to form carboxylic acids on PTFE [46][47][48]. ...
Carbon fiber reinforced polytetrafluoroethylene (CF/PTFE) composites are known for their exceptional tribological performance when sliding against steel or cast iron in inert gas environments. Compared to experiments in humid air, about an order of magnitude lower wear rate and several times lower coefficient of friction have been reported for tests conducted in dry nitrogen and hydrogen. Moreover, trace moisture has been shown to affect the friction and wear significantly of this tribosystem, although a possible effect of oxygen cannot be ruled out due to uncertainties regarding the oxygen concentrations. While several studies have pointed out the environmental sensitivity of CF/PTFE, the understanding of the underlying mechanisms are very limited. The objective of this research is to investigate the individual and combined effect of oxygen and moisture on the tribological behavior of CF/PTFE sliding against steel. Additionally, this study aims to elucidate the underlying mechanisms that govern the environmental sensitivity of the system. Climate-controlled three-pin-on-disc experiments were conducted in nitrogen atmospheres at various concentrations of oxygen and moisture. The tribological results clearly demonstrate that both moisture and oxygen contribute to increased friction and wear. However, the adverse effect was much more pronounced for oxygen than moisture. A qualitative method was developed to estimate the tribofilm coverage on the CF/PTFE surface. Results showed strong correlation between high coverage of strongly adhered tribofilm and low wear rate. Moreover, a loosely adhered tribofilm was observed on top of the CF/PTFE surface in presence of moisture. FTIR analysis indicated that the loosely adhered tribofilm found in the moisture-enriched environment contained a significant amount of adsorbed water, which may explain the lower coefficient of friction in presence of moisture compared to oxygen. The adsorbed water in the loosely adhered tribofilm could be an indication of moisture-driven lubrication by the non-graphitic carbon in the tribofilm.
... Metal carboxylates (metal soaps) commonly present in oil paintings were also detected. The peaks centered around 1538, 1513, 1460 and 1416 cm -1 can be ascribed to lead carboxylates (Otero et al. 2014). Calcium oxalates formed in the surface layers (peak at 1320 cm -1 ) can be related to the atmospheric exposure of old varnish. ...
This work presents the results of a complementary diagnostic investigation carried out on a late wooden panel painting attributed to world-famous Renaissance painter Lucas Cranach the Elder. The aim of this study was to characterize the pigments, ground layers and painting technique used in Cranach’s painting Madonna and Child by means of an integrated nondestructive approach that included Hyperspectral Imaging (HSI), portable X-ray fluorescence
(XRF) and Fourier Transform Infrared Spectroscopy (FTIR). Combined XRF and FTIR data allowed identification of a vibrant color palette, with lead white, verdigris, smalt, vermilion, red
earth, yellow ochre, and a zinc-rich brown earth among the used pigments. Hyperspectral imaging showed no underdrawings, but various technical features and past restoration interventions were
possible to document. The findings provide valuable artistic and technical information regarding the painting materials and style used by this influential 16th-century master, as well as key information that can support the conservation strategy of this remarkable artwork.
... The presence of C-C stretching was indicated by a peak at 1131 cm −1 , while a peak at 1066 cm −1 denotes C-C stretching vibration. Moreover, CH 2 rocking vibration was evidenced by a peak at 903 cm −1 [63,64]. ...
This study investigated the effects of incorporating stearic acid (SAC) in candelilla wax (CW) and groundnut oil (GO) oleogel with potential health benefits as an alternative to saturated fats in processed foods. Results showed that SAC possesses crystal habit-modifying properties on the oleogels, causing its average crystallite size to increase, as observed through polarized light microscopy and XRD analysis. Additionally, SAC caused an increase in ordering within the crystallite network as a result of the decrease in d-spacing. Interestingly, the firmness of the oleogels remained unaffected, even at a higher fraction of SAC. It is believed to be due to the interference caused by the crystallization of high-melting SAC within the fine crystal network of CW-GO oleogel. However, adding 3 mg of SAC significantly increased the work of the shear of the oleogel (SAC3), which decreased the spreadability. As observed through colorimetric analysis, SAC3 showed a dense and uniform distribution of prominent bright crystals with minimal amorphous regions, leading to a high whiteness index. SAC3 also demonstrated the highest compactness and dislocation density among the oleogels, likely due to the formation of prominent crystals. However, SAC did not affect the overall oleogel crystallization rate. SAC3 had delayed secondary crystallization and thermal equilibrium by having a prolonged crystallization time of CW crystals. In the case of controlled delivery studies, the addition of SAC improved CPCR. On the other hand, CPCR decreased with the increase in SAC amount, where SAC3 showed a moderate curcumin release ability among the oleogels.
... 22 The maxima at 400 cm −1 belong to the metal−carboxylate (M−COO) bonds, implying that the organic linker in the AgCo-MOF structure is 1,4-benzene dicarboxylate. 23 The presence of Ag nanoparticles can be observed from the vibrational modes at 633 and 1295 cm −1 , 24 while the peaks at 1355 cm −1 suggest the D band of Co metal. 25 The existence of metal−sulfur (M−S) bond stretching vibrations in the MnS phase was suggested by a peak at 321 cm −1 . ...
... Metal carboxylates (metal soaps) commonly present in oil paintings were also detected. The peaks centered around 1538, 1513, 1460 and 1416 cm -1 can be ascribed to lead carboxylates (Otero et al. 2014). Calcium oxalates formed in the surface layers (peak at 1320 cm -1 ) can be related to the atmospheric exposure of old varnish. ...
This is an original manuscript of an article published by CRC Press in Lasers in the Conservation of Artworks XIII on 3 November 2023 available online: https://doi.org/10.1201/9781003386872-3
... The main characteristic Raman bands of the metal carboxylates as a degradation product are around 1470 cm −1 , which were accurately evaluated using the second derivative. The C-O stretching and CH 2 /CH 3 bending vibrations associated with metal carboxylates were observed approximately at 1465 cm −1 [43,44]. ...
In recent years, the expansion of non-invasive methods has been a trend in identifying historical pigments. Accordingly, this study aimed to identify the pigments used in three Iranian historical manuscripts from the Qajar era by utilizing a non-invasive and multi-analytical approach. A combination of various multi-band imaging methods, along with µ-XRF, Raman and FORS spectroscopy, were employed to identify pigments. The results revealed that emerald green, cochineal, ultramarine, orpiment, and red lead were used as pigments for green, red, blue, yellow, and orange colors on a golden leaf made of brass alloy. The study also demonstrated the mixtures of lead-barite white, lead white-ultramarine and lead white-red lead-indigo-cochineal in the white, light blue, and pink sections. While multi-band imaging was found to be a suitable tool for the primary classification of pigments, relying solely on this method without a complete pigment database is not advisable, as differences in underlying paint layers and mixed pigments can affect imaging results. Overall, the combination of imaging and spectroscopic techniques provides a reliable and non-invasive approach to identifying historical pigments and their alterations.
... FTIR spectra from the paint fragments and cross-sections (Additional file 1: Fig. S6) show the typical peaks associated with fatty acids at ca. 2920, 2850 [v(CH)], and 1710-1730 [ν(CO)] cm −1 , suggesting a lipid-containing binding medium [39]. In most of the samples, IR bands at 1560-1530 cm −1 were also detected, ascribed to the presence of metal carboxylates (Cd and Zn ones [40,41]), formed as a consequence of the reaction of free fatty acids with metal cations or intentionally added to the paint tube formulation as additives [42,43]. Magnesium carbonate (ca 1450, 1415, 875, 820 cm −1 ) was also detected in Mir paint tubes (samples A3 and A6). ...
The deterioration of cadmium yellow paints in artworks by Joan Miró (1893–1983) and in painting materials from his studios in Mallorca (Spain) was investigated. Analysis of samples from Miró’s paintings and from paint tubes and palettes showed that degraded paints are composed of poorly crystalline cadmium sulfide/zinc cadmium sulfide (CdS/Cd1−xZnxS) with a low percentage of zinc, in an oil binding medium. Cadmium sulfates were identified as the main deterioration products, forming superficial white crusts detected using SR µXANES and µXRD techniques. Time-resolved photoluminescence measurements demonstrated that highly degraded samples display a pink/orange emission from the paint surface with a microsecond lifetime, a phenomenon observed in other degraded cadmium yellow paints. In agreement with recent studies on altered cadmium paints, these results suggest that the stability of the paint is related to its manufacturing method, which affects the degree of crystallinity of the resulting pigment. This, together with the environmental conditions in which artworks have been exposed, have induced the degradation of yellow paints in Miró’s artworks. It was finally noted that the paints exhibiting alteration in the analysed Miró artworks have a chemical composition that is very similar to the tube paint ‘Cadmium Yellow Lemon No. 1’ produced by Lucien Lefebvre-Foinet. Indeed, paint tubes from this brand were found in the studio, linking the use of this product with Miro’s degraded artworks.
... It could be suggested that the peaks responded to the presence of fatty acid metal soap. Fatty acid metal soap formation on the painting layers of oil paintings on canvas, and their effect on their preservation, is a known research issue [43][44][45][46][47][48][49][50]. Metal soap formation occurs during the neutralisation of the fatty acids produced by the hydrolytic degradation of oil binders, when the latter react with metal ions in metal hydroxides, oxides, and mixed hydroxide salts, creating an ionomeric-like structure [27,43,44]. ...
Previous works of the authors have presented the changes in the optical, mechanical, and chemical properties of the oiled areas of the supports that occur upon ageing due to oil-binder absorption in works of art on paper and printed material. In this framework, transmittance FTIR analysis has indicated that the presence of linseed oil induces the conditions to promote the deterioration of the oil-impregnated areas of the paper supports. However, the analysis of oil-impregnated mock-ups did not provide detailed information about the input of linseed oil formulations and the different types of paper support on the chemical changes that occur upon ageing. This work presents the results of ATR-FTIR and reflectance FTIR, which were used for compensating the previous results, proving indications on the effect of different materials (linseed oil formulations, and cellulosic and lignocellulosic papers) on the development of chemical changes, thus, on the condition of the oiled areas upon ageing. Although linseed oil formulations have a determining effect on the condition of the oiled areas of the support, the paper pulp content appears to have an input to the chemical changes that occur in the system of paper–linseed oil upon ageing. The results presented are more focused on the oil-impregnated mock-ups with cold-pressed linseed oil since results have indicated that this causes more extended changes upon ageing.
... 57 On the other hand, the sum frequency spectra also show direct evidence for the deprotonated form, primarily through the asymmetric carboxylate stretches centred at ⁓1545 cm -1 and ⁓1590 cm -1 , but also the symmetric carboxylate stretch at ⁓1420 cm -1 . [58][59] Consequently, the headgroup of the vapour deposited stearic acid can be found in both deprotonated (formation of stronger COOˉ … calcium contact ion pairs), and protonated forms (i.e. C=O … calcium ionic interaction). ...
A fundamental understanding of the interactions between mineral surfaces and amphiphilic surface modification agents is needed for better control over production and uses of mineral fillers. Here, we controlled the carboxylic acid layer formation conditions on calcite surfaces with high precision via vapour deposition. The properties of the resulting carboxylic acid layers were analyzed using surface sensitive techniques such as atomic force microscopy (AFM), contact angle measurements, angle resolved X-ray photoelectron spectroscopy (XPS) and vibrational sum-frequency spectroscopy. A low wettability was achieved with long hydrocarbon chain carboxylic acids, such as stearic acid. The stearic acid layer formed by vapour deposition is initially patchy, but with increasing vapour exposure time, the patches grow and condense into a homogeneous layer with a thickness close to that expected for a monolayer as evaluated by AFM and XPS. The build-up process of the layer occurs more rapidly at higher temperatures due to the higher vapour pressure. The stability of the deposited fatty acid layer in the presence of a water droplet increases with chain length and packing density in the adsorbed layer. Vibrational sum frequency spectroscopy data demonstrate that the stearic acid monolayers on calcite have their alkyl chains in an all-trans conformation and are anisotropically distributed on the plane of the surface, forming epitaxial monolayers. The vibrational spectra also show that the stearic acid molecules interact with the calcite surface through the carboxylic acid headgroup in both its protonated and deprotonated forms. The results presented provide new molecular insights into the properties of adsorbed carboxylic acid layers on calcite.
... The FTIR spectrum of sample S-6 showed infrared bands at 1629, 1320 and 782 cm −1 , suggesting the presence of low amounts of calcium oxalates (Frost et al., 2003), in accordance with the XRD analysis above. The presence of calcium stearate/palmitate could be confirmed in sample S-6, as evidenced from the absorption bands at 1576 cm −1 , 1541 cm −1 (asymmetric stretching of COO − ), 1470 cm −1 (in-plane bending of CH 2 ) and 1420 cm −1 (symmetric stretching of COO − ) (Otero et al., 2014;Vichi et al., 2018). With a characteristic absorption band at 3694 cm −1 , a very low amount of brucite (Mg(OH) 2 ) could be discerned as a shoulder peak in the spectra of samples S-1, S-4, S-5 and S-7. ...
Lime mortars have taken an important role in constructing ancient Chinese masonry structures, including city walls, buildings, and tombs. A tomb built with lime mortars and stones belonging a Ming high-rank official Xu Jie was discovered in Huzhou City of China. Eight different samples from Xu Jie’s tomb, representing four types of lime-mortar based materials: joint mortar between stone bricks, bedding mortar, grouting mortar, and plaster mortars were collected for analysis and comparison. The characterization of the construction materials has therefore become of primary importance. The function of each mortar was reported and studies into the micro-textural features and mineralogical compositions of those mortars were performed via a multi-analytical approach. The joint mortars were all found to be aerial lime mortars with predominately lime. The bedding mortar was found to consist of lime, soil and sand, typical of a tabia mortar. The grouting mortar was found to consist of lime and ground contact metamorphosed limestone. Analysis of plaster sample taken from the roof of the main tomb identified the presence of calcium stearate/palmitate, indicating the usage of plant-based Tung oil as an additive. The analytical results will promote our understanding of Ming architectural technology and craftsmanship, and provide critical information for the conservation of Xu Jie’s tomb.
... Beside these bands, other peaks were detected at 1587, 1468, 1450, 1419 and 1316 cm −1 (Figure 4a). Such peaks can be assigned to copper carboxylates, namely palmitates or stearates [27,28]. The same signals were also observed by micro-FTIR spectroscopy on the small green fragment already analyzed by SEM-EDX. ...
Literature reports on Lucio Fontana’s work have focused on the study of the pictorial surface of his paintings. Consequently, to the best of our knowledge, this paper presents the first scientific investigation of gypsum objects made by this artist. These are the gypsum plaster casts made for the construction of the fifth door of the Milan Cathedral, Italy, which were discovered after 60 years, and which showed a green patina and chromatic discolorations. With the aim of understanding the microbiological or chemical nature of the stains, the surfaces of the tiles were investigated by microbiological analysis and analytical techniques including observations by optical, fluorescence and electron microscopy and spectroscopy. The investigated samples showed that the amount of microbiological cells in the stained area was negligible. Chemical analyses allowed the identification of compounds responsible for the chromatic alterations.
... On the contrary, the LIBS analysis revealed that Zn lines (Zn I at 481.1 nm) were more intense at higher pulses (Fig. 4) suggesting that it might be an additive in the preparation layer of MD. The appearance of Zn in the pictorial layer was confirmed via FTIR as well by the detection of zinc carboxylates (degradation products of the interaction of Znbased pigment with the drying oil) via a sharp band ranging between 1537 and 1554 cm -1 for the different samples [27]. Zinc white has been used as a pigment since 1834 [28] which follows the initial estimation that the icons were manufactured in the second half of the 19 th century. ...
This paper studies two 19th century wooden icons from the "Annunciation"
church in Galați, Romania. The artistic materials of the paintings, investigated
through optical microscopy, XRF, LIBS, and FTIR, comprised shellac varnish,
metallic and earth pigments in oil binder in the pictorial layers, and calcite, lipid
binder, gypsum, zinc and lead whites in the preparation layers. One of the icons had
golden embellishment attached to the ground through lead-enriched adhesive of
protein and resin.
These findings shed light on the painting techniques used in Eastern Orthodox
art in the 19th century and also support the restoration process of both icons.
Jean Dunand (1877–1942) was a European artist internationally appreciated at his time for his innovative Art Déco housewares made of hammer‐beaten copper‐based alloys, known as dinanderie . Still uncertain was the nature of the constituting materials; therefore, for the first time, three objects, namely, a bowl, a trinket bowl and a vase, were the target of a multi‐modal work of characterisation. Mobile or benchtop X‐ray fluorescence, Fourier‐transform infrared (FTIR) and Raman spectroscopies were used to adapt the analyses to the shape and size of the artefacts. Elemental analysis verified that the vase consisted of brass Cu 70 Zn 30 , whereas the bowl and the trinket bowl were made of nickel silver Cu 70 Zn 19 Ni 11 . The black finishing present on all the artefacts was related to tenorite by Raman spectroscopy, ascribing the patina to an intentional artist's willing and not to spontaneous tarnishing processes. Metal soaps of copper and zinc were documented as degradation products by FTIR spectroscopy. The drawings adorning the vase and the trinket bowl were identified as silver‐based, contrary to what was hypothesised by conservators (i.e., tin‐based) due to conventional Dunand's inlaying technique. Besides single‐point analysis, Raman mapping was performed in‐situ, applying for the first time a Virsa™ Raman Analyser (Renishaw) in the field of cultural heritage. The fibre‐optic‐coupled instrument allowed to comply constantly with the artefacts' geometry thanks to the modular probe and the motorised focus‐tracking stand. The synergic combination of elemental and vibrational analyses resulted successful, providing new and unique information on artist's technique in view of possible restoration interventions.
With our electrochemical microreactor and the use of an aqueous electrolyte it was possible to realize continuous Kolbe electrolysis including separation of the organic product phase, recycling of the aqueous electrolyte, and automated reconcentration of fatty acids based on inline Raman measurements. Electrolysis experiments revealed that the addition of aqueous KOH is essential to decrease the KHCO 3 concentration and to stabilize the pH value of the electrolyte. Stable conversion (63–58 %) and Kolbe selectivity (90–92 %) could be achieved within 75 min. Removal of KHCO 3 before reconcentration was provided as possible solution to maintain performance for increased electrolysis times.
Superparamagnetic nanoparticles (MNPs) are utilized for magnetic fluid hyperthermia (MFH)-based cancer therapeutics, where the MNPs are surface functionalized to impart desired stability and biological properties. In this study, the MFH properties of palmitic (PA) and stearic (SA) acid-coated superparamagnetic Fe3O4 MNPs, with similar sizes (~ 10 ± 0.8 nm and 11 ± 0.7 nm, respectively), and saturation magnetizations (~ 40.8 emu/g, and ~ 41 emu/g, respectively), are systematically probed to understand the role of the thermo-physical properties of the coating moieties on the MFH efficiency. PA and SA-coated MNPs are prepared using a one-step microwave-assisted co-precipitation technique, and the presence of the surface coatings is confirmed using Fourier transform infrared spectroscopy and thermogravimetric analyses. Magneto-calorimetric studies show a high induction heating efficiency, surpassing the threshold of MFH for a biologically relevant field-frequency range. The maximum heating efficiencies are found to be ~ 164.5 ± 5.4 W/gFe and ~ 223.9 ± 6.4 W/gFe for the PA and SA-coated MNPs, respectively. This indicates ~ 36.1 % higher specific absorption rate (SAR) for the SA-coated MNPs under similar experimental conditions, even though the magneto-structural properties are identical for the PA and SA-coated MNPs. Further, finite element modelling is utilized to investigate the thermal transport from the magnetic core to the surrounding medium, where the thermo-physical properties of the coating moieties are considered. Finite element simulations indicate ~ 32.6 % higher SAR for the SA-coated MNPs, which is consistent with the experimental findings. The higher SAR for the SA-coated MNPs is attributed to the ~ 1.7 times higher thermal diffusivity of SA. The proposed model is experimentally validated using a third system consisting of lauric acid-coated Fe3O4 MNPs with comparable magneto-structural properties. Further, significant temperature rise in a tissue-equivalent agar medium and good bio-compatibility, as indicated by in vitro cyto-toxicity studies, make the prepared MNPs potential candidates for MFH applications. The obtained results provide deeper insight into the role of the thermo-physical properties of the coating moieties on the induction heating efficiency of superparamagnetic MNPs.
Core (Co)/shell (Co-oxide) nanoparticles assembly exhibit interesting magnetic properties that depend on the inorganic shell characteristic (composition and crystalline structure). Assemblies of pure and partially oxidized cobalt (core/shell) nanoparticles, ~9 nm in diameter, were prepared and analyzed by techniques probing the matter at macro- to nano-scale: UV-Visible-NIR transmission, FTIR, Raman microspectroscopy and TEM. Attention is paid to compare non-oxidized and (partially) oxidized Co nanoparticles, coated with lauric acid as stabilizing agent (ligands). The approximately 1 nm disordered inorganic coating is perfectly detected by TEM, UV-visible-NIR, IR and Raman spectroscopy. The Raman spectrum is sensitive to laser wavelength and power due to the local heating induced by the laser, which modifies the interaction between the organic chains and the nanoparticle inorganic shell. For comparison, nanoparticle films were analyzed under heating from room temperature to 300 °C. The "fusion" (dynamic disorder) of lauric (dodecanoic) chains is observed concomitantly with the merging of very low wavenumber Lambs’ modes into a Rayleigh wing, which is consistent with an increase in the topological nanoparticle disorder. Hydroxylation or water adsorption is observed for Co film. The UV-visible-NIR and Raman spectra of the Co-oxide shell do not correspond to that of CoO (rock salt), nor to that of Co3O4 (spinel) but has some similarity to that of 2D delafossite (CoOOH) phase.
In this introduction to the Journal of Raman Spectroscopy special issue “Advanced Raman procedures applied to natural/cultural heritage and forensic questions: Mobile set‐up, data treatment and associated techniques,” the aim is to assess the state of the art in the field and to highlight potential new perspectives. The novel approaches employed in the published papers are described and can be grouped as such: application of multivariate statistical analysis to Raman spectra, use of mobile instrumentations directly in situ for both cultural and forensic contexts, tackling with optics and spectral range issues, and coupling with mobile instrumentations based on different analytical techniques.
The present overview answers the need of assessing the current state of the art concerning the application of principal components analysis (PCA) to Raman spectroscopy investigations of cultural heritage and related materials. An increment of the employment of this multivariate statistic technique to Raman results in the mentioned field began between 15 and 10 years ago, after a very slow start at the turn of the millennium. A delay of about a decade was observed with respect to PCA applied to elemental quantitative data of archaeometric analyses, likely a consequence of the required spectral pre‐treatment and to results of complex interpretation. Therefore, it is by now the time to summarize this evolution in a comprehensive, yet very specific way. In this overview, painting constituents were considered, both colouring materials and binders, in addition to natural and synthetic glasses, and biogenic and mineral gemmological materials. A marked unbalance between the studies pertaining to the different sections has been noticed, revealing a concentration of the work mainly on painting materials, including the study of ageing and alteration. The different aims of PCA application to Raman spectra, the various approaches and the achievable results, with the possible arising problems, were underlined, too. Special attention was given to the pre‐treatment of the spectra, which was observed to be essential to overcome the influence of several issues concerning bands intensity, spectral noise, background, fluorescence and so on.
A fundamental understanding of the interactions between mineral surfaces and amphiphilic surface modification agents is needed for better control over the production and uses of mineral fillers. Here, we controlled the carboxylic acid layer formation conditions on calcite surfaces with high precision via vapor deposition. The properties of the resulting carboxylic acid layers were analyzed using surface-sensitive techniques, such as atomic force microscopy (AFM), contact angle measurements, angle resolved X-ray photoelectron spectroscopy (XPS), and vibrational sum-frequency spectroscopy. A low wettability was achieved with long hydrocarbon chain carboxylic acids such as stearic acid. The stearic acid layer formed by vapor deposition is initially patchy, but with increasing vapor exposure time, the patches grow and condense into a homogeneous layer with a thickness close to that expected for a monolayer as evaluated by AFM and XPS. The build-up process of the layer occurs more rapidly at higher temperatures due to the higher vapor pressure. The stability of the deposited fatty acid layer in the presence of a water droplet increases with the chain length and packing density in the adsorbed layer. Vibrational sum frequency spectroscopy data demonstrate that the stearic acid monolayers on calcite have their alkyl chains in an all-trans conformation and are anisotropically distributed on the plane of the surface, forming epitaxial monolayers. Vibrational spectra also show that the stearic acid molecules interact with the calcite surface through the carboxylic acid headgroup in both its protonated and deprotonated forms. The results presented provide new molecular insights into the properties of adsorbed carboxylic acid layers on calcite.
Relevant virulence traits in Candida spp. are associated with dimorphic change and biofilm formation, which became an important target to reduce antifungal resistance. In this work, Co(II) complexes containing a benzotriazole derivative ligand showed a promising capacity of reducing these virulence traits. These complexes exhibited higher antifungal activities than the free ligands against all the Candida albicans and non-albicans strains tested, where compounds 2 and 4 showed minimum inhibitory concentration values between 15.62 and 125 μg mL⁻¹. Moreover, four complexes (2–5) of Co(II) and Cu(II) with benzotriazole ligand were synthesized. These compounds were obtained as air-stable solids and characterized by melting point, thermogravimetric analysis, infrared, Raman and ultraviolet/visible spectroscopy. The analysis of the characterization data allowed us to identify that all the complexes had 1:1 (M:L) stoichiometries. Additionally, Density Functional Theory calculations were carried out for 2 and 3 to propose a probable geometry of both compounds. The conformer Da of 2 was the most stable conformer according to the Energy Decomposition Analysis; while the conformers of 3 have a fluxional behavior in this analysis that did not allow us to determine the most probable conformer. These results provide an important platform for the design of new compounds with antifungal activities and the capacity to attack other target of relevance to reduce antimicrobial resistance.
Supplementary Information
The online version contains supplementary material available at 10.1186/s13065-023-01037-7.
Using cytotoxic reducing and stabilizing agents in the synthesis of gold nanoparticles (AuNPs) limits their use in biomedical applications. One strategy to overcome this problem is using "green" synthesis methodologies using polysaccharides. In the present study, we propose a green methodology for synthetizing AuNPs with mesquite gum (MG) as a reducing agent and steric stabilizer in Gold(III) chloride trihydrate aqueous solutions to obtain biocompatible nanoparticles that can be used for biomedical applications. Through this method, AuNPs can be produced without using elevated temperatures or pressures. For synthetizing gold nanoparticles coated with mesquite gum (AuNPs@MG), Gold(III) chloride trihydrate was used as a precursor, and mesquite gum was used as a stabilizing and reducing agent. The AuNPs obtained were characterized using UV-Vis spectroscopy, dynamic light scattering, transmission electron microscopy, scanning transmission electron microscopy, and FT-IR spectroscopy. The stability in biological media (phosphate buffer solution), cytotoxicity (MTT assay, hematoxylin, and eosin staining), and hemocompatibility (He-molysis assay) were measured at different concentrations and exposure times. The results showed the successful synthesis of AuNPs@MG with sizes ranging from 3 to 30 nm and a zeta potential of −31 mV. The AuNPs@MG showed good colloidal stability in PBS (pH 7.4) for up to 24 h. Finally, cytotoxicity assays showed no changes in cell metabolism or cell morphology. These results suggest that these gold nanoparticles have potential biomedical applications because of their low cytotoxi-city and hemotoxicity and improved stability at a physiological pH.
The presence of carboxyl groups in a molecule delivers an affinity to metal cations and a sensitivity to the chemical environment, especially for an environment that can give rise to intermolecular hydrogen bonds. Carboxylate groups can also induce intramolecular interactions, such as the formation of hydrogen bonds with donor groups, leading to an impact on the conformational space of biomolecules. In the latter case, the protonation state of the amino groups plays an important role. In order to provide an accurate description of the modifications induced in a carboxylated molecule by the formation of hydrogen bonds, one needs a compromise between a quantum chemical description of the system and the necessity to take into account explicit solvent molecules. In this work, we propose a bottom-up approach to study the conformational space and the carboxylate stretching band of (bio)organic anions. Starting from the anions in a continuum solvent, we then move to calculations using a microsolvation approach including one explicit water molecule per polar group, immersed in a continuum. Finally, we run QM/MM molecular dynamics simulations to analyze the solvation properties and to explore the anions conformational space. The results thus obtained are in good agreement with the description given by the microsolvation approach and they bring a more detailed description of the solvation shell and of the intermolecular hydrogen bonds.
This paper demonstrates the efficacy of portable mid-infrared spectroscopy as a diagnostic tool for revealing the presence of lead carboxylates on artworks, in situ, without sampling. Samples of cerussite and hydrocerussite - the main components of lead white - were separately mixed with linseed oil, and artificially aged in two steps. Their compositional changes have been monitored over time by infrared spectroscopy in two investigation modes: absorption (benchtop instrument) and reflection (portable instrument), and by XRD spectroscopy. Each component of lead white showed different behavior depending on aging conditions, giving important information about the degradation products which are found in real cases. The accordance of results obtained in both modalities demonstrates that portable FT-MIR is a reliable technique for individuating and identifying lead carboxylates directly on paintings. Examples of the efficacy of this application are provided, by studying paintings from the 17th and 18th centuries.
Utilizing carbon dioxide (CO2 ) to make polycarbonates through the ring-opening copolymerization (ROCOP) of CO2 and epoxides valorizes and recycles CO2 and reduces pollution in polymer manufacturing. Recent developments in catalysis provide access to polycarbonates with well-defined structures and allow for copolymerization with biomass-derived monomers; however, the resulting material properties are under-investigated. Here, new types of CO2 -derived thermoplastic elastomers (TPEs) are described together with a generally applicable method to augment tensile mechanical strength and Young's modulus without requiring material re-design. These TPEs combine high glass transition temperature (Tg ) amorphous blocks comprising CO2 -derived poly(carbonates) (A-block), with low Tg poly(ε-decalactone), from castor oil, (B-block) in ABA structures. The poly(carbonate) blocks are selectively functionalized with metal-carboxylates, where the metals are Na(I), Mg(II), Ca(II), Zn(II) and Al(III). The colorless polymers, featuring <1 wt% metal, show tunable thermal (Tg ), and mechanical (elongation at break, elasticity, creep-resistance) properties. The best elastomers show >50-fold higher Young's modulus and 21-times greater tensile strength, without compromise to elastic recovery, compared with the starting block polymers. They have wide operating temperatures (-20 to 200 ˚C), high creep-resistance and yet remain recyclable. In future, these materials could substitute high-volume petrochemical elastomers and be utilized in high-growth fields like medicine, robotics and electronics. This article is protected by copyright. All rights reserved.
The deterioration of cadmium yellow paints in artworks by Joan Miró (1893–1983) and from painting materials from his studios in Mallorca (Spain) was investigated for the first time. Artworks showed discolouration and chalking of paints containing cadmium yellow, altering the colour balance of the works. Analysis of samples from these artworks and from tube paints and palettes containing degraded and non-degraded cadmium yellow paints showed that degraded paints are composed of poorly crystalline CdS/Cd 1 − x Zn x S with a low percentage of Zn in an oil binding medium. Cadmium sulfates were identified as the main deterioration products and their distribution in the paint layers was mapped using SR µXANES and µXRD techniques. Time-resolved photoluminescence measurements demonstrated that highly degraded samples display a peculiar pink/orange emission with microsecond lifetime. In agreement with recent studies on altered cadmium paints, these evidences suggest that the cause of the chemical change of the paint should be related with its manufacturing method, which affects the degree of crystallinity of the resulting pigment and includes the presence of zinc, besides the environmental conditions in which artworks have been exposed. Finally, it is worth noting that the degraded paints in the analysed Miró artworks have a chemical composition very similar to the one of the paint in the tube Cadmium Yellow Lemon No. 1 by Lucien Lefebvre-Foinet . Indeed, paint tubes of this brand were found in the studio, linking the use of this product with Miro’s degraded artworks.
Precise knowledge of the palette employed by historic painters is fundamental to preserving their works of art and can help pinpoint the period in which their paintings were created, their provenance and authorship. Raman and IR spectroscopy is successful in identifying pigments via their molecular spectrum, nevertheless, to distinguish the pigments in a binary mixture is challenging, particularly when the mixed pigments are the same colour and Cu-containing. This is precisely the aim of the current research: to evaluate the effectiveness of the molecular spectroscopy techniques µRS and µFTIR-ATR to discriminate binary mixtures of three green pigments, all containing copper, specifically copper resinate, malachite and verdigris. To that end, two sets of model samples were prepared with pure pigments and their binary mixtures in variable weight concentrations from 20% to 80% for each component. The 15 model samples obtained were mixed with linseed oil in the fixed proportion of 3:1 (w/w) of powdered pigment to binder and spread in a homogeneous layer on a support of commercial grade canvas. Five replicates of µFTIR-ATR and µRS spectra, respectively, were recorded after 0 h, 24 h, 48 h, 72 h and 144 h of exposure within the controlled conditions of a climatic chamber. The aim is to establish the minimum percentage of a Cu-containing pigment in a binary mixture that can be detected by µRS and/or µFTIR-ATR spectroscopy. The product of this ample study is a database of the spectroscopic signature of each pigment in the specific mixtures (in the given proportions and artificial ageing times) for reference purposes in the study of the green areas of selected masterpieces. The oil paintings used in the research (The Nativity, The Visitation, and The Assumption) are of Alonso Cano's work, a well-known artist of the Spanish Golden Age (the Siglo de Oro in Spanish). With this study, the knowledge of the mixture of green pigments employed in Cano's palette was expanded, making considerable progress in the ambitious National Projects in which our Research Group, ever since 2003, has been attempting to understand Cano's technique.
In this thesis, geometry is used as a basis for conducting experiments aimed at growing and arranging inorganic minerals on curved interfaces. Mineralisation is directed using crystalline and liquid-crystalline metallic soaps and surfactant/water systems as templates.¶ A review of the history, syntheses, structure and liquid crystallinity of metallic soaps and other amphiphiles is presented as a foundation to understanding the interfacial architectures in mesostructured template systems in general. ...
Descente des vaches (1836) by Théodore Rousseau in the Mesdag Collection in The Hague is barely readable and its paint layers are in poor condition. The surface of the painting is strongly deformed and cracked, the whole painting has darkened and especially the greens have lost all or most of their colour resulting in brown passages. Large passages of the painting that were painted with multiple thick and medium-rich layers have darkened dramatically. This paper proposes that the degradation of Emerald green (Cu(C2H3O2)2·3Cu(AsO2)2, copperacetoarsenite) – the main green pigment used in this painting – is a significant factor in the cause of the darkening. Electron backscatter images reveal that the Emerald green particles are shown different degrees of degradation: from partially to completely disintegrated. Elemental maps show that arsenic is distributed throughout the paint cross section, with relatively higher concentrations around iron- and aluminium-containing particles, and in the varnish layer. Imaging-Fourier-transform infrared microscopy detects copper soaps in the degraded Emerald green-containing layers. Analytical data from four paint cross sections strongly suggest that Emerald green reacts with free fatty acids derived from the binding medium forming copper soaps and mobile arsenic-based species. Chemical laboratory experiments fully support this hypothesis. Emerald green and palmitic acid in chloroform form copper palmitate and arsenic trioxide (arsenolite, cubic) under room temperature and normal light conditions. The degradation of Emerald green particles in Descente des vaches has resulted in a loss of light-reflecting surfaces and in newly formed compounds in the paint, both contribute to the colour change from green to brown.
This study describes the changes in the infrared spectra of oil paint as a result of aging. The focus is on the influence of pigments on the long-term changes in the oil binding medium. Several naturally aged paints made with different pigments were analysed using Fourier-transform infrared spectroscopy (FTIR). One of the most pronounced effects observed in the infrared spectra of aging paint is the shifting and broadening of the carbonyl band due to the formation of carboxylic acids. Another effect of pigments on the oil binding medium is the catalysis of the hydrolysis of triglycerides, as indicated by the decreasing intensity of the ester absorption. Finally, the nature of the pigment included has a profound effect on the CH stretch absorptions. From these results it is clear that pigments can significantly alter the infrared spectra of drying oil, and should therefore be identified to ensure the correct assessment of the infrared spectra in drying oil paint.
Lead soap aggregateshave been-found in lead-containing oil paint layers in paintings from the thirteenth to the twentieth century. They severely affect the stability of the paint layers and disturb the surface of the paintings. Paint cross-sectionsfrom five paintings affected by lead soaps were selected to illustrate and investigate this degradation phenomenon with the analytical imaging techniques of Fourier transform infrared spectroscopy, secondary ion mass spectrometry and scanning electron microscopy combined with X-ray analysis. Examples aregiven of lead soapsforming in a mature paint system or, alternatively, in the early drying stage of the oil; lead soapsforming from various types of lead-containing pigments or driers; lead soapsforming in multiple paint layers; and lead-containing crystallization products inside aggregates. The phenomenon of lead soap aggregatesis multifaceted, and one general scenario describing theformation of lead soap aggregatescannot explain all aspects. However, the integration of the chemical information and its distribution among the paint layers leads to the proposal that reactivefree monocarboxylicfatty acids playa key role in lead soap aggregateformation. The availability and release of thesefatty acids depends on the original paint composition, the build-up of the layers, and the conservation/environmental exposure history of the painting.
We report for the first time the formation of calcium soaps in paintings. These were characterised by multiple analytical techniques namely FTIR, CI-DTMS and GCMS. A mechanism of formation is proposed based on evidence gathered by 2D and 3D correlative microscopy using light microscopy, SEM-EDX and SRXTM. We propose that the extreme porosity of the clay mineral/chalk/glue ground promotes the absorption of triglycerides from the oil paint binding medium into the ground layer. The presence of clay slightly lowers the pH of the ground layer promoting the instability of the calcium carbonate and facilitating the formation of calcium soaps.
The curing of drying oils at 60°C has been investigated by Fourier transform infrared spectroscopy and Fourier transform Raman
analysis of linseed oil and poppyseed oil. In the first step, hydroperoxides are formed (broad vibration band centered around
3425 cm−1) with concomitant conjugation and cis-trans isomerization of the double bonds (disappearance of cis bands at 3011 and 716 cm−1, appearance of trans conjugated and trans nonconjugated bands at 987 and 970 cm−1). The subsequent decomposition of hydroperoxides in the presence of oxygen leads to the formation of alcohols (nitrite band
at 779 cm−1 after nitrogen monoxide treatment), aldehydes (bands at 2810 and 2717 cm−1 in gas phase), ketones (saturated and unsaturated at 1720 and 1698 cm−1, respectively), carboxylic acids (saturated and unsaturated acid fluorides identified at 1843 and 1810 cm−1 after SF4 treatment), and peresters or γ-lactones (near 1770 cm−1). A rapid decrease in the double-bond concentration is recorded when curing continues, and the formation of epoxides, characterized
by a vibration band at 885 cm−1, is observed. Thermolysis experiments have suggested the proposal of a reaction of addition of peroxyl radicals on the conjugated
double bonds as a probable mechanism. This mechanism explains both the rapid disappearance of conjugated double bonds and
the formation of epoxides as intermediate products observed in the initial step of curing.
The interaction of pigments and binding media may result in the production of metal soaps on the surface of paintings which modifies their visible appearance and state of conservation. To characterise more fully the metal soaps found on paintings, several historically accurate oil and egg yolk tempera paint reconstructions made with different pigments and naturally aged for 10 years were submitted to attenuated total reflectance Fourier transform infrared (ATR FTIR) microspectroscopic analyses. Standard metal palmitates were synthesised and their ATR spectra recorded in order to help the identification of metal soaps. Among the different lead-based pigments, red lead and litharge seemed to produce a larger amount of carboxylates compared with lead white, Naples yellow and lead tin yellow paints. Oil and egg tempera litharge and red lead paints appeared to be degraded into lead carbonate, a phenomenon which has been observed for the first time. The formation of metal soaps was confirmed on both oil and egg tempera paints based on zinc, manganese and copper and in particular on azurite paints. ATR mapping analyses showed how the areas where copper carboxylates were present coincided with those in which azurite was converted into malachite. Furthermore, the key role played by manganese in the production of metals soaps on burnt and raw sienna and burnt and raw umber paints has been observed for the first time. The formation of copper, lead, manganese, cadmium and zinc metal soaps was also identified on egg tempera paint reconstructions even though, in this case, the overlapping of the spectral region of the amide II band with that of metal carboxylates made their identification difficult.
Figure
FTIR false colour plot of the azurite distribution on a selected area of the azurite oil paint reconstruction
General results of the metal soap aggregation survey done between 2002 and 2005 are presented. From the data collected, it is clear there are several degradative phenomena associated with metal soap formation: aggregate formation, efflorescence and changes in transparency. We present a case study of localised darkening due to increased transparency as a result of metal soap formation on the wood grain in a leadwhite-
containing imprimatura layer in a panel painting. Reduced scattering, as a result of the dissolution of the lead
white particles, explains the darkening observed.
To characterize more fully the metal soaps found in paint films or on metal surfaces, several metal soaps were synthesized and their X-ray diffraction pattern and Fourier transform infrared (FTIR) and Raman spectra measured. Metal soaps were obtained from four different fatty acids found in drying oils - two saturated (palmitic and stearic acids) and two unsaturated (oleic and linoleic acids) - and from copper, zinc and lead, three metals that are typically found in metal alloys and paint systems. Data are reported for the following compounds: palmitic acid, stearic acid, oleic acid, linoleic acid, zinc palmitate, zinc stearate, zinc oleate, zinc linoleate, copper palmitate, copper stearate, copper oleate, lead palmitate, lead stearate and lead oleate. Features that are characteristics of specific compounds were observed. Soaps obtained from different fatty acids with the same metal ion show differences, as do soaps obtained with the same fatty acid but with different metal ions. Identification is key to understanding how and why metal soaps form on actual objects, and this may lead to preventive measures.
Chapter 8 is entirely devoted to discussions of the vibrational frequencies of the carbonyl functional group (>CO). Fortunately, the stretching mode of the carbonyl possesses all of the characteristics that give rise to an excellent group frequency. Those factors that perturb the location of the carbonyl in the spectrum are now well understood in terms of theoretical organic chemistry. They are identified as mass, geometric, electronic, and interaction effects. Both first-order and second-order coupling of carbonyls are considered. Also described are examples of intramolecular and intermolecular H-bonding. Field effects and transannular interactions are also examined. The chapter ends with the consideration of amide carbonyl systems.
In order to distinguish aged paint media by FTIR spectroscopy we have focussed on (1) the natural aging of well-defined macroscopic samples of paint media; (2) the modifying effects of typical artists' pigments on the aging of these media; and (3) the utility of these findings in the characterization of unknown media samples. Our key findings are that samples of linseed oil, egg yolk and an emulsion of linseed oil and egg yolk, prepared by R. J. Gettens in the 1930s, exhibit diagnostic IR spectral features well resolved from common inorganic pigment absorptions, thus enabling us to distinguish between these materials and also to detect their presence in authentic, renaissance paintings. Moreover, thermally accelerated aging of freshly prepared linseed oil films yields FTIR spectral features that agree closely with those obtained for the naturally aged Gettens samples of similar initial composition. Our results further demonstrate that the chemical changes associated with either natural or thermally accelerated aging of oil films vary widely with the choice of the inorganic pigment present. Results presented here serve to provide a spectroscopic characterization of the drastic, pigment-dependent chemical changes that have previously hampered the identification of linseed oil on aged paint samples. Successful extension of these results to the spectroscopic analysis of dimensionally resolved layers of paint will be addressed in subsequent publications.
This study demonstrates that resin and fatty acids are able to extract copper (II) ions from verdigris (copper acetate) and verditer (basic copper carbonate). Ligand exchange reactions of basic copper carbonate with fatty acids and resin acids are much slower than is the case with copper acetate. The browning of paint layers is closely correlated with the relative ease of copper extraction; the copper diffuses in the form of fatty acid or resin carboxylic acid complexes. These complexes are formed in the painting layer during grinding of the pigment with binding media containing oleoresin acids, as well as being formed at the interface of this layer and organic upper layers, such as varnishes.
In order to better characterize metal soaps found in paint films or on metal surfaces, several metal soaps were synthesized and their X-ray powder diffraction patterns measured. Metal soaps were obtained from four different fatty acids found in drying oils, two saturated (palmitic and stearic acids) and two unsaturated (oleic and linoleic acids), and from copper, zinc, and lead, three metals that are typically found in metal alloys and paint systems. X-ray powder diffraction data are reported for the following compounds: palmitic acid, stearic acid, zinc palmitate, zinc stearate, zinc oleate, zinc linoleate, copper palmitate, copper stearate, copper oleate, lead palmitate, lead stearate, and lead oleate. Features that are characteristic of specific compounds were observed. Soaps obtained from different fatty acids with the same metal ion show differences, as do soaps obtained with the same fatty acid but with different metal ions. Differences were observed when X-ray powder diffraction data obtained for stearic acid and zinc stearate were compared to published data for these two compounds (PDF 38-1923 and 5-0079, respectively). In the case of stearic acid, differences could be explained by the fact that the specimen reported previously in PDF 38-1923 was likely contaminated with palmitic acid. In the case of zinc stearate, low angle data were missing from the original pattern PDF 5-0079 and peaks that were reported in other angular regions in fact consisted in more peaks that were not resolved due to broadening.
This work describes the application of infrared spectroscopy combined with chemometric tools for the characterization of the proteinaceous binding media used in medieval paints. Historically accurate reconstructions of the most common binders and binder mixtures used in medieval illuminations (egg white, egg yolk, parchment glue and casein glue) were made. Red and blue colors based on vermilion and lapis lazuli were selected as reference paint samples. These two colors were very widely used in medieval illuminations. Different chemometrics methods (supervised and unsupervised), applied to infrared spectral data, were evaluated in terms of their accuracy in the characterization and quantification of complex binding media formulations of the red and blue paints. Principal components analysis and hierarchical cluster analysis revealed that the CH stretching absorption region (3000–2840 cm− 1) and the ester-amides region (1760–1495 cm−1 ) were the best wavenumber region for discriminating the different proteinaceous binders. A regression analysis using classical least squares and partial least squares regression allowed the quantification of binder composition in red and blue paint reconstructions. The restriction to the ester-amide absorption region presented the best spectral reconstruction error and the lowest binder composition reconstruction error.
The infrared spectra of divalent metal tribromoacetates have been measured in the solid state between 4000-400 cm−1. The metal ions are coordinated to the carboxylate group in a manner similar to that found for divalent metal trichloroacetates. However, a significant frequency lowering observed for CC stretch in comparison with the chloroacetates has been attributed to the mass and steric effects of the CBr3 group.
Lead compounds or pigments alter the drying behavior and physical properties of oil paints and varnishes, enabling artists and craftsmen to tailor the properties most suited for their purposes. Investigations into the mechanism of these changes have, however, often been contradictory or misleading. Using modern theories of driers, the behavior of lead additives or pigments can be interpreted or classified.
Publisher Summary
This chapter reviews the group frequencies in terms of the spectral regions in which they occur. The first part of the chapter outlines an orderly procedure for the initial interpretation of an unknown infrared radiation (IR) spectrum by regions. Then, spectra-structure correlations are shown in a chart form where one can look for the groups that absorb in a given region or the regions where a given group absorbs. One of the useful features of infrared spectroscopy is its ability to give information about mixtures. When more than one component is present, the spectra tend to be additive but not completely so because of possible mutual interaction, such as hydrogen bonding for example. If the main component in the spectrum has been identified, a comparison with a reference spectrum may reveal some extra bands in the sample spectrum not in the reference. The chapter also presents some selected Infrared spectra and Raman spectra and illustrates their functional group frequencies.
Lead(II) carboxylate soaps of two fatty acids, palmitic (C15H31COOH) and stearic acids (C17H35COOH), and a dicarboxylic acid, azelaic acid (HOOCC7H14COOH), have been synthesised and characterised by FTIR spectroscopy. These acids are all encountered in aged traditional oil paint, the azelaic acid resulting from the oxidative degradation of unsaturated fatty acids in the oil. Lead(II) azelate synthesised by hydrothermal methods was characterised by single crystal structure determination. This has a 3D polymeric structure with lead(II) ions linked by carboxylate bridges to form an infinite stack of (PbO4)n units. These layers are connected to adjacent layers by an infinite number of parallel C(CH2)7C chains arranged perpendicularly to the stacks. The lead(II) ions display an unusual 7-fold coordination. The first direct evidence that the ‘protrusions’ encountered in aged traditional lead-containing oil paints contain lead soaps is reported. Their mechanism of formation is discussed.
The IR spectra between 1800 and 700 cm−1 of zinc, cadmium and lead carboxylates of even numbered chain length from C6 to C18 inclusive, have been measured as a function of temperature from ambient temperature to a few degrees above the melting point. From the COO− stretching frequencies it is deduced that the coordination of the carboxylate group to the metal ions is unsymmetric chelating bidentate. The only significant change observed prior to the transition point is a decrease in the intensity and a broadening of the progression of the narrow bands between 1350 and 1150 cm− and the band at ca. 720 cm−, most of which virtually disappear in the melt. Above the melting point there is an abrupt change in the shape of the COO − stretching bands. A new band at 1634 cm− is observed in zinc salts. This band has been attributed to the chelating bidentate structure acquiring some monodentate character as the temperature increases. It is found that the spectral changes due to thermal effects are reversible.
The infrared spectra of a series of sodium soaps have been obtained in the range 1800-650 cm.-1 and various features of the spectra from acetate to stearate are discussed. The effect of heat on anhydrous sodium stearate and palmitate has been investigated. The liquid-crystalline form of these soaps is discussed.
Inorganic molecules (ions) and ligands are classified into diatomic, triatomic, four-atomic, five-atomic, six-atomic, and seven-atomic types, and their normal modes of vibration are illustrated and the corresponding vibrational frequencies are listed for each type. Molecules of other types are grouped into compounds of boron, carbon, silicon, nitrogen, phosphorus, and sulfur, and the structures and infrared (IR)/Raman spectra of select examples are shown for each group. Group frequency charts including band assignments are shown for phosphorus and sulfur compounds. Other group frequency charts include hydrogen stretching frequencies, halogen stretching frequencies, oxygen stretching and bending frequencies, inorganic ions, and metal complexes containing simple coordinating ligands.
Raman spectra of biological materials are very complex, because they consist of signals from all molecules present in cells. In order to obtain chemical information from these spectra, it is necessary to know the Raman patterns of the possible components of a cell. In this paper, we present a collection of Raman spectra of biomolecules that can serve as references for the interpretation of Raman spectra of biological materials. We included the most important components present in a cell: (1) DNA and RNA bases (adenine, cytosine, guanine, thymine and uracil), (2) amino acids (glycine, L-alanine, L-valine, L-serine, L-glutamic acid, L-arginine, L-phenylalanine, L-tyrosine, L-tryptophan, L-histidine, L-proline), (3) fatty acids and fats (lauric acid, myristic acid, palmitic acid, stearic acid, 12-methyltetradecanoic acid, 13-methylmyristic acid, 14-methylpentadecanoic acid, 14-methylhexadecanoic acid, 15-methylpalmitic acid, oleic acid, vaccenic acid, glycerol, triolein, trilinolein, trilinolenin), (4) saccharides (β-D-glucose, lactose, cellulose, D-(+)-dextrose, D-(+)-trehalose, amylose, amylopectine, D-(+)-mannose, D-(+)-fucose, D-(−)-arabinose, D-(+)-xylose, D-(−)-fructose, D-(+)-galactosamine, N-acetyl-D-glucosamine, chitin), (5) primary metabolites (citric acid, succinic acid, fumarate, malic acid, pyruvate, phosphoenolpyruvate, coenzyme A, acetyl coenzyme A, acetoacetate, D-fructose-6-phosphate) and (6) others (β-carotene, ascorbic acid, riboflavin, glutathione). Examples of Raman spectra of bacteria and fungal spores are shown, together with band assignments to the reference products. Copyright © 2007 John Wiley & Sons, Ltd.
Oil paintings are complex hybrid materials, made of organic binders associated with inorganic minerals, susceptible to evolving
over centuries. In particular, interactions of oil with lead compounds may give rise to the formation of lead soap aggregates,
so-called protrusions. This phenomenon is studied here via X-ray and FTIR micro-analysis of an ancient painting dated from
1610. In complement, the synthesis of modern preparations, reconstructed from ancient recipes was assessed. Molecular and
atomic images are obtained by combining synchrotron-based FTIR and X-ray fluorescence microscopies. Protrusions are identified
in both ancient and modern samples, more particularly, in the ground layer of the paintings, below the colored layer. These
observations imply that lead oxide, introduced as a siccative and not as a pigment, may be the element mainly responsible
for the protrusions formation, and that this degradation may appear very rapidly on paintings.
The interaction between metals or metallic compounds and polymers is inevitable in the practical use of polymeric articles, and the stability of the polymers is often modified by these materials. Furthermore, the effect of the metallic compounds on the degradation of the polymers is extremely complicated, and is influenced by various factors.This contribution deals with the possible role of metals or metallic compounds in the degradation of polymers, and this is followed by some typical examples of degradation by metallic compounds, mostly commercial pigments and transition metal compounds of stearic acid and acetylacetone, in typical commercial polymers. Recent studies of the inhibition of the copper-catalyzed thermo-oxidative degradation of polyolefins by deactivators, both commercial reagents and novel products, are discussed.
The drying and oxidative degradation of linseed oil have been investigated through exposition of samples in form of thin films to indoor laboratory conditions, or treated at a constant temperature of 80°C, or with irradiation at wavelengths >295 mm. Structure and property changes resulted almost independent of the different treatments and were followed by Fourier transform infrared analysis (FTIR), thermogravimetry (TG), differential scanning calorimetry (DSC), insoluble determination and size exclusion chromatography (SEC). The initial phase of drying consists of the autoxidation phenomenon of the unsaturated fatty acid components with the development of extensive cross-linking, together with formation of conjugated unsaturations. The following stage of slow consumption of labile cross-links gives rise to a highly stable network, which contains small amounts of low molecular weight molecules, either formed by fragmentation or still present as unreacted triglycerides. The oxidative degradation of linseed oil consists of the continuation of the hardening process, and only for long periods of artificial ageing, corresponding to years of natural ageing, the oxidation also takes place on the alkylic segments, leading to partial fragmentation of the structure.
Lead soaps can be found in archaeological cosmetics as well as in oil paintings, as product of interactions of lead salts with oil. In this context, a better understanding of the formation of lead soaps allows a follow-up of the historical evolution of preparation recipes and provides new insights into conservation conditions. First, ancient recipes of both pharmaceutical lead plasters and painting lead mediums, mixtures of oil and lead salts, were reconstructed. The ester saponification by lead salts is determined by the preparation parameters which were quantified by FT-IR spectrometry. In particular, ATR/FT-IR spectrometer was calibrated by the standard addition method to quantitatively follow the kinetics of this reaction. The influence of different parameters such as temperature, presence of water and choice of lead salts was assessed: the saponification is clearly accelerated by water and heating. This analysis provides chemical explanations to the historical evolution of cosmetic and painting preparation recipes.
This work presents Raman spectra obtained from thin films of protein materials which are commonly used as binding media in painted works of art. Spectra were recorded over the spectral range of 3250-250 cm(-1), using an excitation wavelength of 785 nm, and several bands have been identified in the fingerprint region that correspond to the various proteins examined. Differences in the C-H vibrations located between 3200 and 2700 cm(-1) can be accounted for with reference to the amino acid composition of the protein-based binding media as well as the presence of fatty acid esters, in the case of egg yolk. In addition, the discrimination of different proteins on the basis of variations in spectra between 3200 and 2700 cm(-1) can be achieved following multivariate analysis of a large data set of spectra, providing a novel and nondestructive alternative based on Raman spectroscopy to other methods commonly used for the analysis of proteins.
The potential of attenuated total reflection Fourier transform infrared (ATR-FTIR) imaging for the characterisation of the chemical components of paint cross sections from old master paintings was investigated. Three cross sections were chosen to cover a variety of the analytical problems encountered in samples from paintings. The binding medium and degradation products in a green paint sample from a fifteenth-century Florentine painting were imaged, as well as a thin layer within a cross-section from a fifteenth-century German painting, and multiple thin surface coatings on a painting of the 1760s by Peter Romney. The application of chemometric methods for further analysis of the large data set generated for each sample was also explored. The study demonstrated the advantages of ATR-FTIR imaging, which allowed images to be obtained with high spatial resolution (ca. 3-4 microm) without the need to microtome the sample. The gain in sensitivity in detecting trace materials and the information derived from the location of these compounds in the sample was especially valuable, improving interpretation of the FTIR analysis and extending knowledge of the sample composition beyond that obtainable with other analytical techniques.
The Hague, The Netherlands
- J J Boon
J. J. Boon, in Reporting Highlights of the De Mayerne Programme (Eds: J. J. Boon, E. S. B. Ferreira), Netherlands Organisation for Scientific Research (NWO), The Hague, The Netherlands, 2006, pp. 21–32.
Rainford Molecular aspects of mobile and stationary phases in ageing tempera and oil paint films in Early Italian Paintings Techniques and Analysis Symposium Maastricht
- J J Boon
- S Peulvé
- O F Van Denbrink
- M C Duursma
J. J. Boon, S. Peulvé, O. F. van den Brink, M. C. Duursma, D. Rainford, Molecular aspects of mobile and stationary phases in ageing tem-pera and oil paint films in Early Italian Paintings, Techniques and Analysis Symposium, Maastricht, 1997.
The Artist's Assistant: Oil Painting Instruction Manuals and Handbooks in Britain 1800-1900 with Reference to Selected Eighteenth-Century Sources
- L Carlyle
L. Carlyle, The Artist's Assistant: Oil Painting Instruction Manuals and
Handbooks in Britain 1800-1900 with Reference to Selected
Eighteenth-Century Sources, Archetype Publications, London, 2001.
The effects of lead and zinc white saponification on surface appear-ance of paint, ICOM-CC Triennial 15th Conference
- Y Shimadzu
- K Keune
- J J Boon
- J H Townsend
- K J Van
- Berg
Y. Shimadzu, K. Keune, J. J. Boon, J. H. Townsend, K. J. van den Berg, The effects of lead and zinc white saponification on surface appear-ance of paint, ICOM-CC Triennial 15th Conference, New Delhi, 2008.
Changing Pictures: Discoloration in 15th–17th Century Oil Paintings Supporting information Additional supporting information may be found in the online version of this article at the publisher's web site
- M Van Eikema Hommes
M. van Eikema Hommes, Changing Pictures: Discoloration in 15th–17th Century Oil Paintings, Archetype Publications, London, 2004. Supporting information Additional supporting information may be found in the online version of this article at the publisher's web site. V. Otero et al. wileyonlinelibrary.com/journal/jrs Copyright © 2014 John Wiley & Sons, Ltd. J. Raman Spectrosc. (2014)
Keune Chemical processes in aged oil paints affecting metal soap migration and aggregation AIC paintings specialty group postprints Washington
- J J Boon
- F G Hoogland
J. J. Boon, F. G. Hoogland, K. Keune, Chemical processes in aged oil
paints affecting metal soap migration and aggregation, AIC paintings
specialty group postprints, Washington, 2007.