Preliminary study on analysis and removal of wax from a Carrara marble statue

Abstract

This preliminary study has mainly focused on the wax identification by nuclear magnetic resonance (NMR) and removal. Wax is used for many purposes in the field of art as protective coatings on wooden, stone or metal objects. From the comparison of the spectra H NMR and in particular with the correspondence of the resonance peaks of the samples taken from the statue and beeswax and paraffin, we can conclude that the wax applied on the statue surface is beeswax. From our data, it can be concluded that, to remove the beeswax, from any stone support, the more effective solvent is the mixture of cyclohexane/ethyl acetate. The removal percentages ranged from 19 to 99%. Lower percentages of removal have been observed in the case of yellow marble, probably because of its high porosity. We can affirm that, this solvent mixture can be employed in real art objects using cotton swabs to remove protective wax.     

Characterization of wax manufactures of historical and artistic interest

Purpose of this scientific research is the physic and chemical characterization of two historical wax manufactures, made at the end of XIX century by Francesco Bianchi, a papal engraver. The chemical and analytical investigation was necessary to complete and to confirm the restorer's work. The IR Spectroscopy, X-Ray and GC-MS, the best technique to characterise wax, allowed us to obtain the following results. The two manufactures were made with commercial beeswax: in fact, the relative chromatograms showed unchanged peaks about esters of palmitic acid with C24 to C32 alcohol molecules; using standard beeswax we determined the same amount of hydrocarbons present in the wax manufactures. We found several hydrocarbons in these beeswax materials so that it is reasonable to think about successive modifications. ZnO (white zinc), a pigment, was added, probably due to its colour and covering capacity. Sb2S3, Anthimoniun vermilion, a red-orange pigment, was added to these manufactures to give them a soft pink-orange colour. By all used techniques we determined some modifications in the original beeswax; surely they were made to get a more malleable, mouldable, and then more able to be modelled wax.     

Application of surface analysis methods to nanomaterials: summary of ISO/TC 201 technical report: ISO 14187:2011 – surface chemical analysis – characterization of nanomaterials

The ISO technical report 14187 provides an introduction to (and examples of) the information that can be obtained about nanostructured materials by using surface analysis tools. In addition, both general issues and challenges associated with characterizing nanostructured materials and the specific opportunities and challenges associated with individual analytical methods are identified. As the size of objects or components of materials approaches a few nanometers, the distinctions among ‘bulk’, ‘surface’, and ‘particle’ analysis blur. This technical report focuses on issues specifically relevant to surface chemical analysis of nanostructured materials. The report considers a variety of analysis methods but focuses on techniques that are in the domain of ISO/TC 201 including Auger electron spectroscopy, X‐ray photoelectron spectroscopy, secondary ion mass spectrometry, and scanning probe microscopy. Measurements of nanoparticle surface properties such as surface potential that are often made in a solution are not discussed. Copyright © 2012 John Wiley & Sons, Ltd.     

Exploiting the Structural Metamorphosis of Polymers to ‘Wrap’ Micron-Sized Spherical Objects

There is growing interest in developing methods to ‘wrap’ nano- and micron-sized biological objects within films that may offer protection, enhance their stability or improve performance. We describe the successful ‘wrapping’ of lectin-decorated microspheres, which serve as appealing model micron-sized objects, within cross-linked polymer film. This approach utilizes polymer chains able to undergo a structural metamorphosis, from being intramolecularly cross-linked to intermolecularly cross-linked, a process that is triggered by polymer concentration upon the particle surface. Experiments demonstrate that both complementary molecular recognition and the dynamic covalent nature of the crosslinker are required for successful ‘wrapping’ to occur. This work is significant as it suggests that nano- and micron-sized biological objects such as virus-like particles, bacteria or mammalian cells—all of which may benefit from additional environmental protection or stabilization in emerging applications—may also be ‘wrapped’ by this approach.     

Lipidic Matrixes Containing Clove Essential Oil: Biological Activity,Microstructural and Textural Studies

Clove essential oil (CEO) is known for having excellent antioxidant and antimicrobial properties, but the poor stability of its components to light and temperature compromise this activity. The aim of this study is to evaluate the textural, antioxidant, antimicrobial and microstructural properties of matrixes produced with representative natural waxes and CEO. Thus, waxy emulsifiers, such as beeswax, candelilla wax, carnauba wax, and ozokerite wax, were employed to create such matrixes. The thermal, microstructural, textural, wetting, antioxidant, antimicrobial and infrared characteristics of the matrixes were then studied. The diverse chemical composition (long-chain wax esters in carnauba wax and short-chain fatty acids and hydrocarbons in beeswax and ozokerite wax, respectively) explained the differences in wetting, texture, melting, and crystallization characteristics. Crystal forms of these matrix systems varied from grainy, oval, to needle-like shape, but keeping an orthorhombic allomorph. The alignment and reorganization of beeswax and ozokerite wax into needle-like crystals increased the matrix strength and adhesion force compared to those of carnauba and candelilla matrixes, which showed weak strength and grainy morphology. The former two waxes and their matrixes also showed the largest plasticity. These lipidic matrixes show potential use for topical applications having acceptable antioxidant and textural properties.     

Self‐Replenishable Anti‐Waxing Organogel Materials

Solid deposition, such as the formation of ice on outdoor facilities, the deposition of scale in water reservoirs, the sedimentation of fat, oil, and grease (FOG) in sewer systems, and the precipitation of wax in petroleum pipelines, cause a serious waste of resources and irreversible environmental pollution. Inspired by fish and pitcher plants, we present a self‐replenishable organogel material which shows ultra‐low adhesion to solidified paraffin wax and crude oil by absorption of low‐molar‐mass oil from its crude‐oil environment. Adhesion of wax on the organogel surface was over 500 times lower than adhesion to conventional material surfaces and the wax was found to slide off under the force of gravity. This design concept of a gel with decreased adhesion to wax and oil can be extended to deal with other solid deposition problems.     

First results on headspace-solid phase microextraction-gas chromatography/mass spectrometry of volatile organic compounds emitted by wax objects in museums

Sampling volatile organic compounds (VOCs) emitted by a large variety of materials is nowadays a very useful technique for analytical purpose. In the field of cultural heritage, it can be applied to identify some constituents of museum artefacts off-gassing VOCs without sampling on the object itself. In this study, we focused on objects made of wax. First volatiles emitted by a reference beeswax were trapped and identified by headspace-solid phase microextraction (HS-SPME)-gas chromatography and mass spectrometry (GC/MS). This allowed to identify numerous volatile biomarkers, namely saturated n-alkanes from C(10) to C(21), saturated n-carboxylic acids containing 6-12 carbon atoms, benzene and cinnamic derivatives that may be considered as volatile biomarkers of beeswax. The SPME strategy was then performed at the Orsay museum (Paris) in a showcase containing a wax sculpture "Le Mineur de la Loire" by J.-J. Carriès. The use of beeswax in this sculpture was unequivocally confirmed by the VOCs concentrated in the showcase, together with a set of characteristic molecular compounds identified by HT-GC/MS. HS-SPME-GC/MS thus appears to be a powerful in situ and non-invasive analytical technique that allows to identify natural substances in the field of cultural heritage without any sampling of solid matter from the object. The results obtained are promising for orientating the strategy of preventive conservation related to works of art characterised by important emission of VOCs.     

Resolving the Differences Between the 1.9 Å and 1.95 Å Crystal Structures of Photosystem II: A Single Proton Relocation Defines Two Tautomeric Forms of the Water‐Oxidizing Complex

Great progress has been made in characterizing the water‐oxidizing complex (WOC) in photosystem II (PSII) with the publication of a 1.9 Å resolution X‐ray diffraction (XRD) and recently a 1.95 Å X‐ray free‐electron laser (XFEL) structure. However, these achievements are under threat because of perceived conflicts with other experimental data. For the earlier 1.9 Å structure, lack of agreement with extended X‐ray absorption fine structure (EXAFS) data led to the notion that the WOC suffered from X‐ray photoreduction. In the recent 1.95 Å structure, Mn photoreduction is not an issue, but poor agreement with computational models which adopt the ‘high’ oxidation state paradigm, has again resulted in criticism of the structure on the basis of contamination with lower S states of the WOC. Here we use DFT modeling to show that the distinct WOC geometries in the 1.9 and 1.95 Å structures can be straightforwardly accounted for when the Mn oxidation states are consistent with the ‘low’ oxidation state paradigm. Remarkably, our calculations show that the two structures are tautomers, related by a single proton relocation.     

Matrix suppression and analyte suppression effects of quaternary ammonium salts in matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry: an investigation of suppression mechanism

In the matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry (MALDI TOF MS) analysis of some quaternary ammonium salts (QASs), very clean spectra of the quaternary ammonium ions were recorded with a strong matrix suppression effect (MSE). The QASs also showed a considerable analyte suppression effect (ASE). It was demonstrated that the MSE and ASE of the QASs can be explained well by the cluster ionization model. According to this model, MALDI ions are formed from charged matrix/analyte clusters. Various analyte ions and matrix ions might coexist in the cluster, and they will compete for the limited number of net charges available. If enough quaternary ammonium ions are present in the cluster, they will take away the net charges, thus resulting in the MSE and ASE. Our results also suggest that ‘the cluster ionization model’ is not in conflict with ‘the theory of ionization via secondary gas‐phase reactions’. The initial MALDI ions produced from charged matrix/analyte clusters will collide with other molecules or ions in the MALDI plume. Depending on the properties of the initial ions and the composition of the MALDI plume, secondary gas‐phase reactions might result from these collisions. The final ions observed are the combined results of ‘cluster ionization’ and ‘ionization via secondary gas‐phase reactions’. Copyright © 2009 John Wiley & Sons, Ltd.     

Determination of beeswax and some impurities by IR spectroscopy

Summary Analysis of the IR spectra of waxes isolated from samples of paints from paintings dating from the Ist to VIIth centuries of our era and fragments of archaeological antique murals has shown that in some cases the wax isolated is pure beeswax and in others it contains as impurities what are presumably resin acids, and also salts of fatty acids. The IR spectrum of pure beeswax extracted from a fragment buried for 2000 yr is absolutely identical with the spectrum of modern beeswax, which shows the extreme chemical stability of the wax.All-Union Central Scientific-Research Laboratory for Conservation and Restoration, Moscow. Scientific-Research Institute of Organic Intermediates and Dyes, Moscow. Translated from Khimiya Prirodnykh Soedinenii, No. 2, pp. 271–275, March–April, 1977.     

MS2 and Qβ bacteriophages reveal the contribution of surface hydrophobicity on the mobility of non‐enveloped icosahedral viruses in SDS‐based capillary zone electrophoresis

SDS is commonly employed as BGE additive in CZE analysis of non‐enveloped icosahedral viruses. But the way by which SDS interacts with the surface of such viruses remains to date poorly known, making complicate to understand their behavior during a run. In this article, two related bacteriophages, MS2 and Qβ, are used as model to investigate the migration mechanism of non‐enveloped icosahedral viruses in SDS‐based CZE. Both phages are characterized by similar size and surface charge but significantly different surface hydrophobicity (Qβ > MS2, where ‘>’ means ‘more hydrophobic than’). By comparing their electrophoretic mobility in the presence or not of SDS on both sides of the CMC, we show that surface hydrophobicity of phages is a key factor influencing their mobility and that SDS‐virus association is driven by hydrophobic interactions at the surface of virions. The CZE analyses of heated MS2 particles, which over‐express hydrophobic domains at their surface, confirm this finding. The correlations between the present results and others from the literature suggest that the proposed mechanism might not be exclusive to the bacteriophages examined here.     

Transmetalation in the Suzuki–Miyaura Coupling: The Fork in the Trail

The Suzuki–Miyaura coupling is one of the few transition‐metal‐catalyzed C? C bond‐forming reactions that have been used in applications ranging from discovery chemistry to manufacturing processes. Although coupling proceeds through the generic three‐stage ‘oxidative addition, transmetalation, reductive elimination’ sequence, there are a number of features that differentiate the Suzuki–Miyaura process from other transition‐metal‐catalyzed cross‐couplings. Most of these features are centered around, or are a consequence of, activation of the boron reagent for transmetalation through one or both of two distinct pathways. This review focuses on the evidence that has been presented for this ‘fork in the trail′, and the potential to apply such mechanistic insight to the design of reaction conditions.     

Determination of spinosad at trace levels in bee pollen and beeswax with solid–liquid extraction and LC–ESI‐MS

This paper reports the use of a new LC method with a fused‐core analytical column coupled to ESI‐MS to determine residues of the biopesticide spinosad in bee pollen and beeswax. The method analyzes the active ingredients, spinosyns A and D, with a simple and efficient sample treatment (recovery between 90 and 105%) consisting of a solid–liquid extraction with acetone (bee pollen) or acetonitrile (beeswax). The method was validated in terms of selectivity, LOD, LOQ, linearity, and precision. The LOD and LOQ values ranged between 0.1–0.2 and 0.4–0.7 μg/kg, respectively. Moreover, the precision obtained within the linear concentration range (LOQ 500 μg/kg) was satisfactory (RSD lower than 5%). Finally, the proposed method was applied to analyze bee pollen and beeswax samples collected from apiaries located close to fruit orchards in two Spanish regions.     

Oral cancer diagnostics based on infrared spectral markers and wax physisorption kinetics

Infrared microspectroscopy is an emerging approach for disease analysis owing to its capability for in situ chemical characterization of pathological processes. Synchrotron-based infrared microspectroscopy (SR-IMS) provides ultra-high spatial resolution for profiling biochemical events associated with disease progression. Spectral alterations were observed in cultured oral cells derived from healthy, precancerous, primary, and metastatic cancers. An innovative wax-physisorption-based kinetic FTIR imaging method for the detection of oral precancer and cancer was demonstrated successfully. The approach is based on determining the residual amount of paraffin wax (C₂₅H₅₂) or beeswax (C₄₆H₉₂O₂) on a sample surface after xylene washing. This amount is used as a signpost of the degree of physisorption that altered during malignant transformation. The results of linear discriminant analysis (LDA) of oral cell lines indicated that the methylene (CH₂) and methyl group (CH₃) stretching vibrations in the range of 3,000–2,800 cm^?1 have the highest accuracy rate (89.6 %) to discriminate the healthy keratinocytes (NHOK) from cancer cells. The results of wax-physisorption-based FTIR imaging showed a stronger physisorption with beeswax in oral precancerous and cancer cells as compared with that of NHOK, which showed a strong capability with paraffin wax. The infrared kinetic study of oral cavity tissue showed a consistency in the wax physisorption of the cell lines. On the basis of our findings, these results show the potential use of wax-physisorption-based kinetic FTIR imaging for the early screening of oral cancer lesions and the chemical changes during oral carcinogenesis.

One‐Pot ‘On‐solvent’ Multicomponent Protocol for the Synthesis of Medicinally Relevant 4H‐Pyrano[3,2‐c]quinoline Scaffold

‘One‐pot’ AcONa‐catalyzed transformation of salicylaldehydes, malononitrile and 4‐hydroxy‐1‐methylquinolin‐2(1H)‐one in the presence of a minimal quantity of EtOH results in fast (3 min) and efficient formation of unknown 2‐amino‐4‐(2‐hydroxyaryl)‐6‐methyl‐5‐oxo‐5,6‐dihydro‐4H‐pyrano[3,2‐c]quinoline‐3‐carbonitriles in 85–98% yields, which are potential pharmaceutical agents for treating disorders responsive to the induction of apoptosis, antiproliferation, or vascular disruption. This efficient ‘on‐solvent’ approach to the 4H‐pyrano[3,2‐c]quinoline scaffold represents a novel synthetic concept for multicomponent reaction (MCR) strategy and allows to combine the synthetic virtues of conventional MCR with ecological benefits and convenience of facile ‘on‐solvent’ procedure.     

Raman spectroscopic analysis of Mexican natural artists' materials

This work represents the Raman spectra of 15 natural artists' materials that were obtained from local market in Mexico. Some of these products are not endemic to the region, but are often used in local conservation practice. Other materials are of local origin and have been used for centuries by local craftsmen. The Raman spectra that are reported here are: Chia oil, linseed oil, Campeche wax, beeswax, white copal, dammar, colophony, mastic, pixoy, chapopote, chucum, aje gum, gutta gum, peach gum and gum Arabic. The sample of pixoy was mixed with TiO(2), although it was not clear whether this was done intentionally or not. The Raman spectrum of chapopote, the local name for bitumen, contained features of carbonaceous and terpenoid matter. The Raman spectra of chapopote and chucum suffered severely from fluorescence, resulting in noisy Raman spectra. Aje gum and gutta gum are not gums, since they are resinous (terpenoid) in nature. Aje is a rare animal resin originating from Coccus axin.     

Identification and structural characterization of the synthetic cannabinoid 3‐(1‐adamantoyl)‐1‐pentylindole as an additive in ‘herbal incense’

Since the end of 2010, more than 20 synthetic cannabimimetics have been identified in ‘Spice’ products, demonstrating the enormous dynamic in this field. In an effort to cope with the problem, many countries have already undertaken legal measures by putting some of these compounds under control. Nevertheless, once a number of compounds were scheduled, they were soon replaced by other synthetic cannabinoids. In this article, we report the identification of a new – and due to its substitution pattern rather uncommon – cannabimimetic found in several ‘herbal incense’ products. The GC–EI mass spectrum first led to misidentification as the alpha‐methyl‐derivative of JWH‐250. However, since both substances show different retention indices, thin‐layer chromatography was used to isolate the unknown compound. After application of nuclear magnetic resonance spectroscopy, high‐resolution MS and GC–MS/MS techniques, the compound was identified as 3‐(1‐adamantoyl)‐1‐pentylindole, a derivative of JWH‐018 carrying an adamantoyl moiety instead of a naphthoyl group. This finding supports that the listing of synthetic cannabinoids as prohibited substances triggers the appearance of compounds with uncommon substituents. Moreover, it emphasizes the necessity of being aware of the risk of misidentification when using techniques sometimes providing only limited structural information like GC–MS. Copyright © 2012 John Wiley & Sons, Ltd.     

Analytical characterization of natural waxes employing pyrolysis–gas chromatography–mass spectrometry

Three natural waxes (bleached beeswax, lanolin, yellow carnauba wax) were investigated by means of pyrolysis–gas chromatography–mass spectrometry (Py–GC–MS). Pyrograms were obtained showing very characteristic signal patterns. Mass spectrometric detection enabled the structural identification of the pyrolytically formed fragments. For a more detailed investigation of the thermal degradation behaviour of waxy materials, relevant model compounds were selected. Hexadecylpalmitate, cholesterylstearate, heptadecanoic acid and 1-hexacosanol were examined under identical Py–GC–MS conditions. From the resulting product distribution general statements were able to be derived according to the thermal degradation pathways of typical wax constituents. The findings obtained from the model compounds were then applied to the interpretation of the real wax pyrograms. As a result, conclusions according to their origin from corresponding wax constituents were drawn for the majority of pyrolysis products. Thus, the extended potential of the method for the compositional analysis of natural waxes is demonstrated.     

Characterisation of beeswax in works of art by gas chromatography-mass spectrometry and pyrolysis-gas chromatography-mass spectrometry procedures

Pyrolysis (Py) with in situ derivatisation with hexamethyldisilazane-gas chroma-break tography-mass spectrometry (GC-MS) and a gas chromatography-mass spectrometry procedure based on microwave-assisted saponification were used to identify the organic components in small sized beeswax samples. With the latter procedure quantitative recoveries can be made and hydrocarbons, alcohols and omega-1-diols in the neutral fraction, and fatty acids and omega-1-hydroxy acids in the acidic fraction can be efficiently separated and detected. Both procedures were used to characterise a wax anatomic sculpture "The Plague" (1691-1694) by Gaetano Zumbo, resulting in the identification of beeswax and a Pinaceae resin. The GC-MS analysis brought to light some essential differences in beeswax composition between the raw material and the old modelled wax thus giving some clear indications about the recipe used by the sculptor.     

Analytical characterization of corrosion products of copper and its alloys on stained stone surfaces

Monuments, where stone and metals or metallic alloys are used together, are very frequently met in all historical periods and in all countries. In the case of bronze and other copper alloys, their corrosion products can be dissolved by the action of acid rain and thus reach the porous building materials in contact with (or near to) the metallic structures. Once absorbed by the stone, they precipitate on the external stone surface and inside its porous space. As the majority of these products are coloured, their precipitates may produce stains, which are perceived as unpleasant alterations of the original ‘values’ of the stone monuments. The removal of stains is therefore required on the occasion of conservation treatments. The paper reports on the characterisation of copper corrosion products found on two, very different, monuments in Rome: ‘Fontana delle Tartarughe’ (by T. Landini, last quarter of the 16th century) and ‘Statua dello Studente’ (by A. Cataldi, 1920). To identify the speciation of copper compounds in their carbonate matrices, different techniques [X‐ray diffraction, X‐ray fluorescence, SEM/energy‐dispersive X‐ray spectroscopy (EDS), micro‐Raman and XPS] had to be employed. To further confirm the identification of the chemical species, SEM/EDS data were also processed by principal component analysis. Copyright © 2013 John Wiley & Sons, Ltd.