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

Wax, Wings, and Swarms: Insects and Their Products as Art Media

Every facet of human culture is in some way affected by our abundant, diverse insect neighbors. Our relationship with insects has been on display throughout the history of art, sometimes explicitly but frequently in inconspicuous ways. This is because artists can depict insects overtly, but they can also allude to insects conceptually or use insect products in a purely utilitarian manner. Insects themselves can serve as art media, and artists have explored or exploited insects for their products (silk, wax, honey, propolis, carmine, shellac, nest material), body parts (e.g., wings), and whole bodies (dead, alive, individually, or as collectives). This review surveys insects and their products used as media in the visual arts and considers the untapped potential for artistic exploration of media derived from insects. The history, value, and ethics of insect media art are relevant topics at a time when the natural world is at unprecedented risk.

First Evidence of "Earth Wax" Inside the Casting Molds from the Roman Era

This research was focused on the analysis of material composition and organic residues present in three molds found in the Moravian region (Czech Republic) belonging to the Roman era. X-ray fluorescence spectroscopy pointed out the possible remelting of Roman objects in Barbarian territory. The analysis of organic residues retrieved from the internal part of mold #2 by pyrolysis-gas chromatography/mass spectrometry proved the presence of ozokerite wax (“earth wax”). Consequent analysis of this organic residue by Atmospheric Solids Analysis Probe–ion mobility spectrometry–high-resolution mass spectrometry (ASAP-IMS-HRMS) confirmed the presence of ceresin, the main component of ozokerite. Ceresin was also detected in a sample of the organic residue from mold #1. Note that this is the first application of ASAP-IMS-HRMS in archaeological research. The remains of earth wax in molds suggest the production of wax models as an intermediate stage for the production of lost-wax ceramic casting molds.

Profiling of high molecular weight esters by flow injection analysis-high resolution mass spectrometry for the characterization of raw and archaeological beeswax and resinous substances

This work presents a method to characterize high molecular esters in beeswax and resinous substances based on the use of microwave-assisted extraction and flow injection analysis-high resolution mass spectrometry that combines the high efficiency of the extraction procedure with the advantages of high resolution mass spectrometry. This approach allows us to identify archaeological beeswax and plant resinous substances by the characterization of the survived intact high molecular weight components. By this way, several raw materials (beeswax, pine resin and pitch, and resin extracted from Euphorbia tirucalli) were studied and used as reference substances. The procedure was then tested on an adhesive dated 44-42 ka BP recovered from Border Cave (KwaZulu-Natal, Africa), allowing us to detect the high molecular weight species even after almost 50,000 years, and then used to chemically investigate unknown archaeological adhesives from Antinoopolis (Egypt), dated to the 4th-5th century AD. The results allowed us to extend our knowledge on the long-term behavior of beeswax and resinous substances.

A multi-analytical study of a wall painting in the Satyr domus in Córdoba, Spain

In this work, we conducted a careful study of the mortar and paint in the Roman wall painting housed by the triclinium of the so-called Domus in the Road Safety Education Park of Córdoba, Spain. A combination of X-ray diffraction, Raman and X-ray fluorescence spectroscopies allowed the different substances used to obtain the pigments present in the painting to be identified. The painting was found to contain five different colours (red, yellow, blue, green and white) in various hues. The red pigment was obtained from hematite and the yellow pigment from goethite. The blue pigment, which was the least abundant, was prepared from Egyptian blue, and the green pigment from green earths. Finally, the white pigment came from lime. The binders used were identified by infrared spectroscopy and gas chromatography with mass spectrometry detection. The painting fragments studied contained vestiges of bee wax or its decomposition products, which suggests that the paint was applied encaustically.

Hafting of Middle Paleolithic tools in Latium (central Italy): New data from Fossellone and Sant'Agostino caves

Hafting of stone tools was an important advance in the technology of the Paleolithic. Evidence of hafting in the Middle Paleolithic is growing and is not limited to points hafted on spears for thrusting or throwing. This article describes the identification of adhesive used for hafting on a variety of stone tools from two Middle Paleolithic caves in Latium, Fossellone Cave and Sant’Agostino Cave. Analysis of the organic residue by gas chromatography/mass spectrometry shows that a conifer resin adhesive was used, in one case mixed with beeswax. Contrary to previous suggestions that the small Middle Paleolithic tools of Latium could be used by hand and that hafting was not needed since it did not improve their functionality, our evidence shows that hafting was used by Neandertals in central Italy. Ethnographic evidence indicates that resin, which dries when exposed to air, is generally warmed by exposure to a small fire thus softened to be molded and pushed in position in the haft. The use of resin at both sites suggests regular fire use, as confirmed by moderate frequencies of burnt lithics in both assemblages. Lithic analysis shows that hafting was applied to a variety of artifacts, irrespective of type, size and technology. Prior to our study evidence of hafting in the Middle Paleolithic of Italy was limited to one case only.

Gas chromatography/mass spectrometry techniques for the characterisation of organic materials in works of art

The power of GC/MS to resolve, characterise and quantify complex mixtures of organic compounds with high sensitivity has made it an indispensable analytical tool to address detailed questions about the chemical constituents of works of art. This paper provides an overview of the technique and its particular suitability to material studies of art and historical artefacts, and reviews its diverse research applications concerning the organic composition of artists’ and conservation materials. Options with regard to sample preparation by chemical derivatisation, pyrolysis techniques, and methods for the analysis of volatile organic compounds are discussed, as well as various approaches to the treatment and interpretation of data. The greatest value is gained from GC/MS when it is used as a complementary technique, informed by and in synergy with other methods of analysis.

A new strategy based on microwave-assisted technology for the extraction and purification of beeswax policosanols for pharmaceutical purposes and beyond

Policosanols (PCs) are a mixture of long chain primary aliphatic alcohols mainly known for their ability to reduce cholesterol level. Due to this property, there is an increasing interest in the extraction process of these compounds. In this context, beeswax, a natural product produced by honey bees of the genus Apis, is a promising source for their extraction and purification. The present research work was aimed at the development of a new procedure for the extraction and purification of PCs from yellow beeswax by using microwave-assisted technology, which hitherto has never been applied to this mixture. The developed process comprises three main steps: 1) microwave-assisted trans-esterification; 2) microwave-assisted hydrolysis; 3) final purification by means of preparative liquid chromatography. The final step is responsible for the increased purity of PCs, thanks to the removal of undesired compounds, such as natural paraffins. The predominant alcohols investigated in this work are tetracosanol (C₂₄OH), hexacosanol (C₂₆OH), octacosanol (C₂₈OH), triacontanol (C₃₀OH) and dotriacontanol (C₃₂OH). Compound identification was performed using GC-EI-MS, while GC-FID analysis was chosen for the quantification of the main fatty alcohols present in the product. This new method represents a useful tool for the production of PCs from beeswax to be used in pharmaceuticals and nutraceuticals for human use, feed and veterinary supplements.

Phytochemical Findings Evidencing Botanical Origin of New Propolis Type from North-West Argentina

Propolis samples from north-west Argentina (Amaicha del Valle, Tucumán) were evaluated by palynology, FT-IR spectra, and RP-HPTLC. In addition, the volatile fraction was studied by HS-SPME-GC/MS. The botanical species most visited by Apis mellifera L. near the apiaries were collected and their RP-HPTLC extracts profiles were compared with propolis samples. In addition, GC/MS was performed for volatile compounds from Zuccagnia punctata Cav. (Fabaceae). FT-IR spectra and RP-HPTLC fingerprints of propolis samples showed similar profiles. In RP-HPTLC analyses, only Z. punctata presented a similar fingerprint to Amaicha propolis. The major volatile compounds present in both were trans-linalool oxide (furanoid), 6-camphenone, linalool, trans-pinocarveol, p-cymen-8-ol, and 2,3,6-trimethylbenzaldehyde. Potential variations for the Amaicha del Valle propolis volatile fraction as consequence of propolis sample preparation were demonstrated.

An Enhanced GC/MS Procedure for the Identification of Proteins in Paint Microsamples

The chemical characterization of materials used in works of art is extremely useful for gaining a better knowledge of the artistic heritage and to guarantee its preservation. A derivatization GC/MS procedure for the identification of proteins in a microsample from painted works of art has been optimized. The amino acid fraction is derivatized using anhydrous dimethylformamide (DMF) as solvent instead of pyridine (Py), commonly used to facilitate the reaction. Although pyridine is often considered a silylation catalyst, there are many instances in which silylation reactions actually are slower in pyridine than other solvents. In addition, pyridine also may have other undesirable effects such as the promotion of secondary products and other chromatographic anomalies. Using DMF, the formation of artifacts is limited and the derivatization yield of hydrophilic amino acids such as proline and hydroxyproline has improved, thus making the identification of organic paint media more straightforward. The method has been validated and successfully applied to identify the binder of the sample taken from the pictorial cycle of the 12th century monastery of Santa Maria delle Cerrate (Lecce, Italy), thus highlighting the use of eggs as a binding medium.

Simultaneous qualitative and quantitative evaluation of Ilex kudingcha C. J. tseng by using UPLC and UHPLC-qTOF-MS/MS

In this study, a systematic method was established for the holistic quality control of Ilex kudingcha C. J. Tseng, a popular functional drink for adjuvant treatment of diabetes, hypertension, obesity and hyperlipidemia. Both qualitative and quantitative analyses were conducted. For qualitative analysis, an ultra high performance liquid chromatography (UHPLC) coupled with an electrospray ionization quadrupole time-of-flight mass spectrometry (ESI-qTOF-MS) method was established for rapid separation and structural identification of the constituents in Ilex kudingcha. Samples were separated on an ACQUITY UPLC HSS T3C₁₈ column (2.1 mm × 100 mm, 1.8 μm) by gradient elution using 0.1% (v/v) formic acid (solvent A) and acetonitrile (solvent B) as mobile phases at a flow rate of 0.25 mL min^-1. The chromatographic profiling of Ilex kudingcha by UHPLC-qTOF-MS/MS resulted in the characterization of 53 compounds, comprising 18 compounds that were unambiguously identified by comparison with reference standards. For quantitative analysis, 18 major compounds from 15 batches of Ilex kudingcha samples were simultaneously detected by UPLC-DAD at wavelengths of 210 nm, 260 nm, and 326 nm. The method was validated with respect to precision, linearity, repeatability, stability, accuracy, and so on. The contents of the 18 target compounds were applied for hierarchical clustering analysis (HCA) and principal component analysis (PCA) to differentiate between the samples. The results of HCA and PCA were consistent with each other. Sample No. 1 differed significantly based on HCA and PCA, and the differentiating components were confirmed to originate from different batches of samples. Phenolic acids and triterpenes were found to be the main ingredients in Ilex kudingcha. This strategy was effective and straightforward, and provided a potential approach for holistic quality control of Ilex kudingcha.

Identification of proteins, drying oils, waxes and resins in the works of art micro-samples by chromatographic and mass spectrometric techniques

Simplified method for simultaneous identification of proteins, drying oils, waxes, and resins in the works-of-art samples was developed. Liquid chromatography with mass spectrometry and gas chromatography with mass spectrometry were used to identify natural materials most frequently encountered in historical paintings. Protein binders were extracted with ammonia and purified using miniaturized solid-phase microextraction (Omix tips) to efficiently suppress matrix interferences. Zwitterionic stationary phase was used for separation of 16 underivatized amino acids analysis with hydrophilic interaction liquid chromatography that was subsequently quantified with liquid chromatography with mass spectrometry. Gas chromatography with mass spectrometry was used to analyze drying oils, waxes, and resins after one-step saponification/transmethylation with (m-trifluoromethylphenyl)trimethylammonium hydroxide (Meth-Prep II). While the drawback of this reagent is low reactivity towards hydroxyl groups, sample pretreatment was much simpler as compared to the other methods. Fatty acids derivatization with the Meth-Prep II reagent was compared with their silylation using N,O-bis(trimethylsilyl) trifluoroacetamide/trimethylchlorosilane mixture. It was concluded that fatty acids analysis as their methyl esters instead of trimethylsilyl esters had a minor impact on the method sensitivity. The developed method was used to analyze samples from 16^th and 17^th century historical paintings.

Preparation of Modified Beeswax and Its Influence on the Surface Properties of Compressed Poplar Wood

Beeswax was modified through the direct blending of nano-TiO₂, chitosan, acid dyes, and neutral dyes. With the varied modified beeswax, hot waxing was conducted on compressed poplar wood. Treated wood surfaces were characterized with scanning electron microscopy and thermogravimetric analysis. Results show that the C, O, N, Au, S, and Ti elements in modified beeswax successfully penetrated into pits of compressed poplar wood, imparting rich colors to the wood surface. The blending of 10% (mass fraction) beeswax, 0.2% chitosan, and 0.05% neutral red was the best treatment for mulation for improving the in-surface staining uniformity, durability, surface gloss, contact angle, and texture conspicuity of compressed poplar.

Analytical Approaches Based on Gas Chromatography Mass Spectrometry (GC/MS) to Study Organic Materials in Artworks and Archaeological Objects

Gas chromatography/mass spectrometry (GC/MS), after appropriate wet chemical sample pre-treatments or pyrolysis, is one of the most commonly adopted analytical techniques in the study of organic materials from cultural heritage objects. Organic materials in archaeological contexts, in classical art objects, or in modern and contemporary works of art may be the same or belong to the same classes, but can also vary considerably, often presenting different ageing pathways and chemical environments. This paper provides an overview of the literature published in the last 10 years on the research based on the use of GC/MS for the analysis of organic materials in artworks and archaeological objects. The latest progresses in advancing analytical approaches, characterising materials and understanding their degradation, and developing methods for monitoring their stability are discussed. Case studies from the literature are presented to examine how the choice of the working conditions and the analytical approaches is driven by the analytical and technical question to be answered, as well as the nature of the object from which the samples are collected.

Method for the determination of natural ester-type gum bases used as food additives via direct analysis of their constituent wax esters using high-temperature GC/MS

Natural ester-type gum bases, which are used worldwide as food additives, mainly consist of wax esters composed of long-chain fatty acids and long-chain fatty alcohols. There are many varieties of ester-type gum bases, and thus a useful method for their discrimination is needed in order to establish official specifications and manage their quality control. Herein is reported a rapid and simple method for the analysis of different ester-type gum bases used as food additives by high-temperature gas chromatography/mass spectrometry (GC/MS). With this method, the constituent wax esters in ester-type gum bases can be detected without hydrolysis and derivatization. The method was applied to the determination of 10 types of gum bases, including beeswax, carnauba wax, lanolin, and jojoba wax, and it was demonstrated that the gum bases derived from identical origins have specific and characteristic total ion chromatogram (TIC) patterns and ester compositions. Food additive gum bases were thus distinguished from one another based on their TIC patterns and then more clearly discriminated using simultaneous monitoring of the fragment ions corresponding to the fatty acid moieties of the individual molecular species of the wax esters. This direct high-temperature GC/MS method was shown to be very useful for the rapid and simple discrimination of varieties of ester-type gum bases used as food additives.

Towards identification of traditional European and indigenous Australian paint binders using pyrolysis gas chromatography mass spectrometry

We report a pyrolysis GC-MS method capable of analysing Indigenous Australian and European binders typically used in the manufacture of culturally important painted works. Eleven different traditional European binders and ten different Indigenous Australian binders were examined. The method allows discrimination between highly complex and impure lipid, resin, polysaccharide, wax, and protein-based binders. Each was found to have characteristic pyrolysis products that were unique to the binder material, demonstrating the potential for differentiation of these binders on Australian Aboriginal artworks towards identification and conservation of cultural heritage.

Mass Spectrometric and Synchrotron Radiation based techniques for the identification and distribution of painting materials in samples from paints of Josep Maria Sert

Background

Establishing the distribution of materials in paintings and that of their degradation products by imaging techniques is fundamental to understand the painting technique and can improve our knowledge on the conservation status of the painting. The combined use of chromatographic-mass spectrometric techniques, such as GC/MS or Py/GC/MS, and the chemical mapping of functional groups by imaging SR FTIR in transmission mode on thin sections and SR XRD line scans will be presented as a suitable approach to have a detailed characterisation of the materials in a paint sample, assuring their localisation in the sample build-up. This analytical approach has been used to study samples from Catalan paintings by Josep Maria Sert y Badía (20^th century), a muralist achieving international recognition whose canvases adorned international buildings.

Results

The pigments used by the painter as well as the organic materials used as binders and varnishes could be identified by means of conventional techniques. The distribution of these materials by means of Synchrotron Radiation based techniques allowed to establish the mixtures used by the painter depending on the purpose.

Conclusions

Results show the suitability of the combined use of SR μFTIR and SR μXRD mapping and conventional techniques to unequivocally identify all the materials present in the sample and their localization in the sample build-up. This kind of approach becomes indispensable to solve the challenge of micro heterogeneous samples. The complementary interpretation of the data obtained with all the different techniques allowed the characterization of both organic and inorganic materials in the samples layer by layer as well as to establish the painting techniques used by Sert in the works-of-art under study.

Chemical investigation on black pigments in the carved decoration of sixteenth century alabaster tombs from Zaragoza (Spain)

An analytical protocol based on optical microscopy (OM), scanning electron microscopy (SEM) observation, energy-dispersive X-ray (EDX) analyses, analytical pyrolysis in the presence of hexamethyldisilazane followed by gas chromatographic/mass spectrometric analysis (Py-silylation-GC/MS) and gas chromatography/mass spectrometry (GC/MS) after alkaline hydrolysis, solvent extraction and trimethylsilylation was used to study the origin and nature of black pigments from the carved inscriptions of several panels of two alabaster tombs dated from the mid-sixteenth century. Optical microscopy and SEM observation showed the presence of an amorphous very dark-brown substance, from translucent to opaque. EDX analyses revealed that the samples were mainly made up of C and O, thus highlighting the organic nature of the material used in the inscriptions. Py-silylation-GC/MS and GC/MS analyses provided detailed molecular compositions, highlighting the presence of a wide range of compound classes including diterpenoid acids, tricyclic abietanes, mid- and long-chain monocarboxylic fatty acids, n-alkanols and nalkanes. The pyrograms, the chromatographic profiles and the presence of characteristic biomarkers indicated that a mixture of pine pitch and beeswax had been used to make the black inscriptions.

Py-GC/MS, GC/MS and FTIR investigations on Late Roman-Egyptian adhesives from opus sectile: new insights into ancient recipes and technologies

An analytical protocol based on optical microscopy, Fourier transforms infrared spectroscopy (FTIR), analytical pyrolysis in the presence of hexamethyldisilazane followed by gas chromatographic/mass spectrometric analysis (Py-GC/MS) and gas chromatography/mass spectrometry after alkaline hydrolysis, solvent extraction and trimethylsilylation (GC/MS) was used in the chemical characterisation of the original adhesives used to fix monochrome and mosaic glass and stone plaques coming from the Late Roman archaeological site of Antinoopolis (Egypt). FTIR analysis demonstrated the presence of calcite fragments, and Py-GC/MS and GC/MS analyses provided detailed molecular compositions, highlighting the presence of a wide range of compound classes including diterpenoid acids, tricyclic abietanes with a high degree of aromatisation, mid- and long-chain monocarboxylic fatty acids, mono- and di-hydroxy acids, alpha,omega-dicaboxylic fatty acids, n-alkanols, and n-alkanes. Characteristic biomarkers and their distribution patterns indicated the presence of pine pitch in all the adhesives, which in some cases was admixed with beeswax and brassicaceae seed oil. The results provided new insights into the complex recipes used by artisans in ancient Egypt in the production of adhesives and in the sophisticated manufacture of opus sectile decorations.

Identification of predominant odorants in thai desserts flavored by smoking with "Tian Op", a traditional Thai scented candle

"Tian Op", a traditional Thai scented candle, is used for the smoking and flavoring of sweets, cakes, and other desserts for the purpose of adding a unique aroma to the final product. Gas chromatography-olfactometry, aroma extract dilution analysis, and GC-MS were applied to identify the potent odorants in two types of traditional Thai desserts ("num dok mai" and "gleep lum duan") prepared using a Tian Op smoking process. On the basis of the results of AEDA and calculated odor-activity values, the predominant odorants in the Tian Op flavored desserts were vinyl ketones (C(5)-C(9)), n-aldehydes (C(5)-C(11)), (E)-2-unsaturated aldehydes (C(8)-C(11)), and omega-1-unsaturated aldehydes (C(8) and C(9)). Sensory studies of model mixtures confirmed the importance of n-aldehydes, omega-1-unsaturated aldehydes, and guaiacol as predominant odorants; however, the results showed that vinyl ketones and (E)-2-unsaturated aldehydes, despite having high odor-activity values, may be of only minor importance in the typical aroma profiles of traditional Tian Op smoked desserts.

Novel analytical methods for characterising binding media and protective coatings in artworks

Since the first reported analytical studies and technical examinations of art and archaeological objects conducted in the late 18th century, analytical techniques and methods applied to the study of artworks have constantly grown. Among the materials composing the art object, organic compounds used as binding media or protective coatings have attracted the attention of the conservation profession given their noticeable ability for undergoing morphological and chemical changes on ageing. Thus, the aim of this paper is to review the most recent advances in the identification and determination of organic compounds present in art and art conservation materials. Immunofluorescence techniques have been proposed in recent decades as an alternative to the classical and simpler microchemical tests. Besides, a variety of instrumental techniques have also been improved in an attempt to enhance the sensitivity, repeatability and accuracy of the analytical results. Spectroscopic techniques, such as UV-vis, FTIR and Raman spectroscopy, have been coupled with light microscopes for these purposes. Synchrotron radiation FTIR microspectroscopy has also been successfully applied to the analysis of artworks. Mass spectrometry has also been increasingly used as a detector system coupled with a chromatographic device. Chromatographic methods have also improved in recent years. Paper and thin layer chromatographic techniques have been progressively replaced with gas chromatography (GC), pyrolysis-GC, high performance liquid chromatography and capillary electrophoresis. More complex proteomics hyphenated techniques, such as nano-liquid chromatography-nano-electrospray ionisation/collision quadrupole time-of-flight tandem mass spectrometry, have been recently applied to the identification and determination of proteinaceous binders. Microbeam analytical techniques have also been incorporated into the list of advanced instrumental techniques for art conservation purposes. Finally, a number of new instrumental techniques have been proposed as a suitable alternative to the conventional microscopy techniques for morphological studies.

Levoglucosan and other cellulose markers in pyrolysates of Miocene lignites: geochemical and environmental implications

Using the pyrolysis-gas chromatography-mass spectrometry and off-line pyrolysis/silylation methods for lignites from three Miocene brown coal basins of Poland resulted in the characterization of many organic compounds, including dominant cellulose degradation products such as levoglucosan, 1,6-anhydro-beta-D-glucofuranose, and 1,4:3,6-dianhydroglucopyranose. Levoglucosan is a general source-specific tracer for wood smoke in the atmosphere and recent sediments. The presence of unusually high levels of this compound in brown coal pyrolysates suggests that a portion of this compound concentration in some airsheds may originate from lignite combustion. On the other hand, nonglucose anhydrosaccharides, in particular, mannosan and galactosan, typical of hemicellulose, are not detected in those lignite pyrolysates investigated. This indicates that mannosan and galactosan are better specific tracers for combustion of contemporary biomass in those regions were the utilization of brown coals containing fossilized cellulose is important.

Calibration of Raman spectroscopy at 1064 nm for beeswax quantification

In the early sixties, coating with molten beeswax was considered a valuable method for preventing the erosive action of weather and/or salinity on the surface of granite sculptures and monuments. This technique had been traditionally employed by the Galician stoneworkers for partial repair of historical monuments. For this purpose, beeswax was applied to the Renaissance Frieze in the Cloister of the Cathedral of Santiago de Compostela in Galicia (Northwest Spain). The beeswax treatment was counterproductive. An intense grain disaggregation of the granite can be observed in the Frieze, owing to the crystallization of salts. As a consequence, the restoration of the Cloister presents many problems. This fact imposes the need for an exhaustive study of the wax-stone system and the demand for a nondestructive method to measure the beeswax thickness at the stone surface. The aim of this contribution is the evaluation of a laser-based method, namely Fourier transform Raman spectroscopy, for analyzing the wax presence in specific rocky material of the Frieze to be restored. To obtain a reliable quantitative calibration, we prepared beeswax films of five different thicknesses on aluminum plates (26.6-97.2 microm). Nylon was selected as external reference to obtain the Raman emission independently from the laser beam power. The ratios of the relative intensities of the Raman bands corresponding to beeswax and nylon were used for the construction of a calibration curve used for the quantitative analysis. The intensities at 2879 cm(-1), I(c2879), and 2880 cm(-1), I(n2880), for beeswax and nylon, respectively, in the Raman spectra of each material were used. A linear dependence was found for the ratio I(c2879)/I(n2880) with the beeswax thickness. The validation of this calibration curve was tested with a second validation set of samples that spans beeswax film thicknesses both inside and outside the calibration range (12.1 to 180 mum), in order to evaluate in addition the accuracy of the model at extrapolation. Without complex sample preparation, near-infrared Raman spectroscopy resulted in an effective technique for localizing the wax with lateral resolution of tens of micrometers, and for determining wax layer thickness in the stone with an uncertainty of a few micrometers.

Analysis of diterpenoic compounds in natural resins applied as binders in museum objects by capillary electrophoresis

The exudates of conifers consist mainly of diterpenoic acids of the abietane and pimarane type (abietic, neoabietic, dehydroabietic, palustric, pimaric, isopimaric, levopimaric and sandaracopimaric acid) and larixol acetate. These natural resins were used as adhesives, coatings, varnishes or plasticizers in artistic and historic works since ancient times. For the purpose of conservation and restoration and for art historic examination of such museum objects the identification of the binding media used is undoubtedly of paramount importance. In the present paper, the characterization of these resins based on the pattern of their diterpenoid constituents is carried out by capillary electrophoresis. For separation a background electrolyte which has been initially introduced for the analysis of chlorinated and natural resin acids in waste water was modified and the experimental conditions were adjusted in terms of resolution and analysis time. Separation was carried out in borate buffer at pH 9.25 (ionic strength 20 mmol L(-1)) with methyl-beta-cyclodextrin and sulfobutylether-beta-cyclodextrin as additives to increase selectivity and enhance the solubility of the analytes. With this electrophoretic system the resin acids of interest and larixol acetate--all as anionic cyclodextrin complexes--were separated within 5 min and detected at 200, 250 and 270 nm with a diode array detector. The electrophoretic patterns served for the characterisation of the relevant diterpenoic resins, balsams and copals. Sample pre-treatment was limited to sonication in methanol at 55 degrees C for 30 min. This enables the identification of the resins in mixtures with other binders like plant gums, animal glues or drying oils, even when these media are present in excess. Colophony was identified as resinous constituent of a modelling mass for gilded frames originating from the 19th century.

Elucidation of molecular and elementary composition of organic and inorganic substances involved in 19th century wax sculptures using an integrated analytical approach

Wax sculptures contain several materials from both organic and inorganic nature. These works of art are particularly fragile. Determining their chemical composition is thus of prime importance for their preservation. The identification of the recipes of waxy pastes used through time also provides valuable information in the field of art history. The aim of the present research was to develop a convenient analytical strategy, as non-invasive as possible, that allows to identify the wide range of materials involved in wax sculptures. A multi-step analytical methodology, based on the use of complementary techniques, either non- or micro-destructive, was elaborated. X-ray fluorescence and micro-Raman spectroscopy were used in a non-invasive way to identify inorganic pigments, opacifiers and extenders. The combination of structural and separative techniques, namely infrared spectroscopy, direct inlet electron ionisation mass spectrometry and high temperature gas chromatography, was shown to be appropriate for unravelling the precise composition of the organic substances. A micro-chemical test was also performed for the detection of starch. From this study it has been possible to elucidate the composition of the waxy pastes used by three different sculptors at the end of the 19th century. Complex and elaborated recipes, in which a large range of natural substances were combined, were highlighted.

Combined GC/MS Analytical Procedure for the Characterization of Glycerolipid, Waxy, Resinous, and Proteinaceous Materials in a Unique Paint Microsample

A novel GC/MS analytical procedure for the identification of lipids, waxes, proteins, and resinous materials in the same microsample from painted works of art has been optimized. It is based on a sample multistep chemical pretreatment (solvent extractions and microwave-assisted chemolysis) that is able to separate the various organic components into different fractions, which are suitably treated and derivatized before analysis. In particular, the procedure allows the complete saponification of wax esters and the completeness of the Cannizzaro type reaction of shellac acids in conditions that are suitable also for glycerides saponification. The method was tested on reference materials for the identification of proteinaceous binders (egg, collagen, casein) on the basis of the quantitative determination of the amino acid profile and the identification of glycerolipids (linseed oil, poppy seed oil, walnut oil, and egg), plant resins (Pinaceae resins, sandarac, mastic, and dammar), animal resins (shellac), tars or pitches, and natural waxes (beeswax, carnauba wax) on the basis of the determination of fatty acid, alcohol, and hydrocarbon profiles and of significant terpenic molecular markers. The procedure was applied to the characterization of three old paint microsamples. Animal glue, egg, linseed oil, beeswax, Pinaceae resin, dammar, and shellac were the identified materials found in mixtures and recognized as original and/or restoration substances.

Multianalytical Study of Laser Pulse Duration Effects in the IR Laser Cleaning of Wall Paintings from the Monumental Cemetery of Pisa

The feasibility of laser cleaning for the removal of a variety of surface deposits from fragments of real wall paintings from the monumental cemetery of Pisa using Nd:YAG at 1064 nm at (μs), (ns), and (ps) regimes is presented. Multianalytical investigations of the samples from irradiated surfaces of fragments were carried out in order to characterize the original and added materials and to detect any laser-induced alterations; analysis included scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), laser-induced breakdown spectroscopy (LIBS), pyrolysis-gas chromatography-mass spectrometry (PY-GC-MS), and gas chromatography-mass spectrometry (GC-MS). The presence of nitrocellulose and pure lead contaminations on the surface of the samples has been identified. Assessment of the laser cleaning has highlighted the importance of the optimization of laser parameters, specifically pulse duration and fluence at the specified wavelength.

Characterisation of wax works of art by gas chromatographic procedures

To identify the various natural and synthetic substances used by sculptors at the end of the 19th century, several contemporary reference samples were investigated by high temperature gas chromatography (HT GC) and HT GC-MS. Using specific chromatographic conditions and minimising sample preparation, we could separate, detect and identify a wide range of biomolecular markers covering a great variety of molecular weights and volatilities, with a minimum amount of sample, in a single run. Beeswax, spermaceti, carnauba, candellila and Japan waxes as well as pine resin derivatives, animal fats, paraffin, ozokerite and stearin, used as additives in wax works of art, were chemically investigated. In the case of low volatile compounds, transbutylation was performed. The structure of long-chain esters of spermaceti was elucidated for the first time by HT GC-MS analysis. Such a method was then carried out on 10 samples collected on a statuette of Junon by Antoine-Louis Barye (Louvre Museum, Paris, France) and on a sculpture by Aimé-Jules Dalou (Musée de la Révolution Française, Vizille, France). The analytical results obtained provide new data on the complex recipes elaborated by sculptors at the end of the 19th century.

Characterization of waxes used in pictorial artworks according to their relative amount of fatty acids and hydrocarbons by gas chromatography

A study attempted to characterize natural waxes used in pictorial works of art was carried out by means of gas chromatography. The analytical treatment requires prior hydrolysis of the waxes to release the fatty acids (FA) (myristic (myr), palmitic (pal), oleic (ole), stearic (ste), araquidic (ara), behenic (beh), lignoceric (lig), cerotic (cer)) from the main esters of the waxes. The formation of volatile derivatives of the fatty acids was carried out by derivatization with ethyl choroformate (ECF). This derivatization reagent was chosen due to the speed, safety and quantitativity of the reaction. The analyzed hydrocarbons were n-eicosane, n-heneicosane, n-docosane, n-tricosane, n-tetracosane, n-pentacosane, n-hexacosane, n-heptacosane, n-octacosane, n-nonacosane, n-tricontane n-hentriacontane, n-dotriacontane, n-tritriacontane, n-tetratriacontane, n-pentatriacontane, main constituents of the waxes. No derivatization is needed to analyze the hydrocarbons. Ethyl ester derivatives and hydrocarbons are adequately separated by gas chromatography, identified by flame ionization detection and confirmed by mass spectrometry. To characterize natural waxes, peak area ratios of each fatty acids with respect to the palmitic acid and peak area ratios of each hydrocarbons with respect to n-heptacosane were calculated. The proposed method provides a good characterization of different waxes most frequently used in artworks, such as beeswax, carnauba wax and ceresin, and has been successfully applied to real samples. This is the first report on the application of ECF to the analysis of fatty acids in wax.