GC-MS characterisation and identification of natural terpenic resins employed in works of art

Natural resins were frequently employed in the past as adhesives or as components of oleo-resinous media in paintings. The identification of vegetable resins is still an open problem. The aim of this paper is to analyse by GC-MS some vegetable resins frequently employed in paintings, such as Venice turpentine, dammar, copal, elemi, in order to identify their main components in samples both raw and aged. Some molecules are proposed as chemical markers to identify these natural resins. Two samples scraped off from XV and XVII century paintings were used to test the reliability of proposed method.     

Natural products such as adhesives in oil paintings

Abstract

The study and analysis of the materials employed in artistic paintings provide deeper knowledge about the history of the work of art, including restoration efforts made in the past, and the development of painting techniques through the centuries. Gas chromatography coupled to mass spectrometry is the main analytical technique employed, as it proved to be the most suitable technique for the analysis of complex mixtures, thanks to its combination of sensitivity, wide range of applicability and versatility. Further, μFT-IR technique has also been employed to get a preliminary screening of the samples taken from paintings. In this paper, the analytical protocol based on these two techniques has been applied for analysing natural terpenic resins; its performance has been tested on microsamples collected from paintings of valuable artistic interest.     

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.     

Study of Burseraceae resins used in binding media and varnishes from artworks by gas chromatography-mass spectrometry and pyrolysis-gas chromatography-mass spectrometry

In the present work, a study attempting to characterize the Manila elemi and Mexican copal resins from the Burseraceae family, which are used as components of varnishes and binding media of artworks, has been carried out. A new GC-MS method involving the use of methyl chloroformate as derivatisation reagent has been proposed. A second method which uses pyrolysis-GC-MS and hexamethyldisilazane as derivatization reagent has also been applied. Characterization of the main components of the mono-, sesqui- and triterpenoid fractions occurring in the raw materials has been achieved. Both alpha- and beta-amyrin have been established as the major triterpenoid compounds occurring in these resins together with hop-22(29)-en-3beta-ol, found only in the Mexican copal. Artificially aged samples of Manila elemi and Mexican copal have also been analysed in order to study the stability of the triterpenoid components of the resins and their possible use as marker molecules. The results obtained indicate that these molecules, in particular, alpha- and beta-amyrin undergo oxidation processes during both artificial and natural ageing. Nevertheless, hop-22(29)-en-3beta-ol could be selected as marker compound for Mexican copal. The proposed methods of analysis have been applied to real paint samples extracted from paintings in which Mexican copal was present as the main component of an "oleoresin" binding medium to assess their ability for identifying this product when used in artworks. Satisfactory identification of this resin is obtained by means of GC-MS whereas Py-GC-MS provides, in general, weaker signals for the components of the resin. Additionally, the influence of the pigments present in real samples on the resin ageing process has been considered.     

Study of Complex Organic Binding Media Systems on Artworks Applying GC-MS Analysis: Selected Examples from the Kunsthistorisches Museum,Vienna

Within the Kunsthistorisches Museum (KHM), Vienna, three off-line GC-MS analytical procedures for the identification of natural organic media have been refined, tested, and validated for the use in investigating original, historic works of art. The analysis of a sample from a Greek terracotta statue suggested that the white ground layer of the polychromy, still partly present today, contained a gum-based binding medium. Furthermore, a procedure for the simultaneous analysis of oils, waxes and resins was applied to the identification of the composition of the varnish layer from the 16^th century painting “Lucretia” by Jacopo Negretti (1480–1528). In addition, in a collaboration with the Department for Conservation and Restoration, University of Applied Arts, Vienna, a series of samples from paintings on wooden panels from the Buddhist temple complex in Nako, Himachal Pradesh, India, was investigated for the presence of proteinaceous binding media.     

Fourier transform infrared spectroscopy and the analytical study of works of art for purposes of diagnosis and conservation

This paper is a study of the analytical capacity of Fourier transform infrared spectroscopy (FT-IR) for any type of samples from works of art. The analytical information obtained with this technique on organic and inorganic compounds is extremely useful in the preliminary studies necessary for diagnosis and to decide on the conservation process. This paper reports the analysis and study with FT-IR on samples extracted from the microlayers in several works of art from different periods (16th to 18th century) comprising wall paintings and canvas. The most outstanding of these being the frescoes by A. Palomino from two ceilings in the Santos Juanes church. The analytical procedures for the different components of the works studied such as

1. (a) varnish applied to wood panels and canvas paintings,

2. (b) binding media and pigments used by the artists,

3. (c) inerts, mortars, stuccos and grounds have been optimized. The FT-IR technique offers a quick analysis of microsamples (less than 0.5 mg) and is able to characterise the different molecular groups which provide information on the nature of the different materials of organic and inorganic origin used by the artist and thus permits the diagnosis of pathologies requiring conservation treatment.

Methodology and application of gc-ms to study altered organic binding media from objects of the Kunsthistorisches Museum, Vienna

Within the Kunsthistorisches Museum (KHM), Vienna, three off-line GC-MS analytical procedures for the identification of natural organic media have been refined, tested, and validated on a series of reference materials (partly artificially aged) to apply this knowledge for investigations of original, historic works of art from the museum's collections. At first, a set of artificially aged mockups has been prepared and a reference database has been built up for the identification of drying oils, resins, waxes, proteins and polysaccharides. Some interesting observations concerning the alteration of the composition of these organic media during different ageing steps are presented in the following text. In addition, some selected examples for the application of the refined techniques for the analysis of real samples from various museum objects are shown.     

Identification and differentiation of dragon's blood in works of art using gas chromatography/mass spectrometry

Dragon's blood is a common but non-specific name for red-coloured resins that are produced by various plants, particularly exudations from plant species belonging to the genera Dracaena and Daemonorops. Although dragon's blood is mentioned in historic sources as a colourant, it has hardly ever been identified in real artworks. This paper reports the identification and discrimination of dragon's blood produced by Dracaena cinnabari, Dracaena draco as well as Daemonorops draco and Daemonorops micracantha by means of gas chromatography/mass spectrometry (GC/MS) within the context of a routine analysis of binding media used in works of art. The detection of specific flavonoid marker compounds in both underivatised and methylated methanol extracts provided the first evidence for the use of dragon's blood from all four species in various works of art from the fifteenth to nineteenth centuries. Dragon's blood was mainly used as a red colourant in gold lacquers as well as translucent glazes and paints, e.g. in reverse-glass paintings (Hinterglasmalerei).     

Voltammetric methods applied to identification, speciation, and quantification of analytes from works of art: an overview

Voltammetry of microparticles, an electrochemical methodology based on the record of the voltammetric response of sparingly soluble solids mechanically transferred to the surface of inert electrodes in contact with suitable electrolytes, is able to provide significant analytical information in the fields of conservation and restoration of cultural goods. Using this methodology, identification, speciation, and relative and absolute quantification of analytes from works of art samples can be achieved. Applications to the analysis of organic and inorganic pigments in paints, fibbers, ceramic materials as well as alteration compounds in paintings and metallic artifacts are reviewed.     

Chromatographic,Microscopic, and Spectroscopic Characterization of a Wooden Architectural Painting from the Summer Palace,Beijing, China

The wooden construction painting is a type of an ancient decorative art on Chinese ancient structures. Comprehensive reports concerning the composition of these materials are rather limited. Here multiple analytical methods were applied to systematically explore the morphology and materials. Several paintings were characterized using a morphological microscope. Scanning electron microscopy–energy dispersive spectrometry (SEM-EDS), X-ray fluorescence (XRF), and X-ray diffraction (XRD) detected emerald green and ultramarine in the paint layers. Gas chromatography–mass spectrometry (GC-MS) indicated that the binding medium in the first layer was composed of blood. Our study helps to comprehensively understand the preparation of the wooden construction paintings in the renowned Summer Palace and provide a scientific basis for its restoration and related archeology work.     

Detecting art forgeries using LA-ICP-MS incorporating the in situ application of laser-based collection technology

The nature of art lends itself to forgery as a skilled and determined forger can mimic the techniques and styles of an artist to a level where even an expert can be duped. The authentication of paintings is a subjective process, but modern techniques may provide the means to provenance artist pigments based on elemental composition. This study applies laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) to the analysis of artist paints from different manufacturers to identify variation between the elemental association patterns of these materials. The technique facilitates comparison of the paints used by an artist with produced works of art to assist provenancing initiatives of questioned materials. The effects of the trace element profiles of the backing substrate and binder on analytical data were also identified. By applying the technique to paint scraped from real paintings, a limited database was created to allow comparison to be made with some of Australian artist, Kathleen O’Connor's artworks and assist in determining production chronology. Data from this study were able to facilitate comparison of blue paints from two different paintings and confirm their co-provenance consequently determining the relative production date of a separate painting of previously unknown age.Preliminary trials of a prototype collection device designed to reduce damage and allow for in situ sampling of artworks were also undertaken. The device, which allows direct laser-based sampling of a complete painting, was tested using a Francis Ryan painting. The prototype allows for the collection of debris directly generated by LA-ICP-MS of a predefined area of a painting prior to subsequent analysis using direct LA-ICP-MS. This collection method significantly minimizes the amount of damage produced by conventional sampling methods. Analyses of the debris collected, using the prototype, were found to be comparable to the scrapings of equivalent paint analysed using direct LA-ICP-MS analysis.     

Advanced combined application of μ-X-ray diffraction/μ-X-ray fluorescence with conventional techniques for the identification of pictorial materials from Baroque Andalusia paintings

The process of investigating paintings includes the identification of materials to solve technical and historical art questions, to aid in the deduction of the original appearance, and in the establishment of the chemical and physical conditions for adequate restoration and conservation. In particular, we have focused on the identification of several samples taken from six famous canvases painted by Pedro Atanasio Bocanegra, who created a very special collection depicting the life of San Ignacio, which is located in the church of San Justo y Pastor of Granada, Spain. The characterization of the inorganic and organic compounds of the textiles, preparation layers, and pictorial layers have been carried out using an XRD diffractometer, SEM observations, EDX spectrometry, FT-IR spectrometry (both in reflection and transmission mode), pyrolysis/gas chromatography/mass spectrometry and synchrotron-based μ-X-ray techniques. In this work, the advantages over conventional X-ray diffraction of using combined synchrotron-based μ-X-ray diffraction and μ-X-ray fluorescence in the identification of multi-layer paintings is demonstrated.     

Electrochemistry for conservation science

Voltammetry of microparticles, an electrochemical methodology based on the record of the voltammetric response of sparingly soluble solids mechanically transferred to the surface of inert electrodes in contact with suitable electrolytes, is able to provide significant analytical information in the fields of conservation and restoration of cultural goods. Using this methodology, identification, speciation, and relative and absolute quantification of analytes from works of art samples can be achieved. Applications to the analysis of organic and inorganic pigments in paints, fibbers, ceramic materials as well as alteration compounds in paintings and metallic artifacts are reviewed.     

Characterization of polyvinyl resins used as binding media in paintings by pyrolysis–silylation–gas chromatography–mass spectrometry

Polyvinyl resins, in particular poly(vinyl acetate) emulsions (PVA), are widely used in contemporary paintings as binding media, because of the optimum mechanical and optical properties these polymers confer on the paint layers. A study has been carried out to chemically characterize samples of PVA resins prepared as coating films from commercial products currently available from fine arts suppliers. For this purpose, a new method has been based on "on-line" silylation-pyrolysis using hexamethyldisilazane as derivatisation reagent in pyrolysis-gas chromatography-mass spectrometry (Py-GC-MS). This proposed procedure leads to unambiguous identification of this type of binder and improves conventional direct Py-GC-MS. PVA media used in three contemporary paintings from a private collection and from the Museum of Fine Arts of Málaga (Spain) have been successfully identified with this procedure. As a second step of this work, a study devoted to the characterization of changes in the chemical composition of the PVA commercial products studied has been carried out. Effects induced in the specimens by three different types of artificial accelerated ageing process--thermal, UV light, and in an SO(2)-polluted chamber--were compared.     

Natural resins and balsams from an eighteenth-century pharmaceutical collection analysed by gas chromatography/mass spectrometry

Historical nomenclature has not always been unequivocally associated with the botanical origin of natural resins. The availability of natural resins has changed throughout the centuries and so have their trade names. Furthermore, adulterations and lack of knowledge have led to variations in the composition of the products traded under the same name. This investigation aims at a new understanding of the interrelation between the historical and modern terms for natural resins. Different Pinaceae and Pistacia resins, mastic, sandarac, copaiba balm and burgundy pitch from Vigani’s Cabinet, a 300-year-old pharmaceutical collection owned by Queens’ College, Cambridge (UK) were investigated. Related reference materials from modern collections were analysed together with natural resins derived from reliable botanical sources. The analytical method was gas chromatography/mass spectrometry (GC-MS) with and without derivatisation with trimethylsulfonium hydroxide. This technique provided detailed molecular compositions of the studied materials, which in turn led to particular data profiles of the materials. Marker molecules of Copaifera, Pinaceae, Cupressaceae and Pistacia resins were identified. By comparing the GC-MS data profiles to the reference samples, a clearer picture of the connection between nomenclature and botanical origin was obtained. With the aid of the marker molecules and data profiles, it was then possible to clarify the nomenclature of the aged resins sampled from Vigani’s Cabinet.     

Archaeological resinous samples from Asian wrecks: Taxonomic characterization by GC-MS

Plant resins, and particularly dammars from the Dipterocarpaceae family, were widely used in the past, notably as part of caulking material. The organic composition of resins, already complicated, is not always preserved over time and can be considerably affected by ageing. Hence, their occurrence in archaeological items leads to the necessity to identify them taxonomically with precision. Resinous organic materials collected near and/or on wrecks discovered in South China Sea, supposed to contain dammar resins because of their geographical excavation context, were investigated by gas chromatography-mass spectrometry (GC-MS), together with freshly collected dammars, to establish taxonomic and alteration parameters allowing to identify dammar even in very altered samples or in mixtures together with other organic materials. This study specially focuses on three samples collected within or close to the M1J wreck, a Portuguese wreck lost in the Straight of Malacca during the 16th century. Our analyses establish that all three are made of dammar, two of them in association with pitch and bitumen. In addition, biodegradation biomarkers were detected in all these three samples, indicating that they were submitted to microbial degradation processes during their ageing.     

Tracing the biological origin of animal glues used in paintings through mitochondrial DNA analysis

We report the development of a suitable protocol for the identification of the biological origin of binding media on tiny samples from ancient paintings, by exploitation of the high specificity and high sensitivity offered by the state-of-the art DNA analysis. In particular, our aim was to molecularly characterize mitochondrial regions of the animal species traditionally employed for obtaining glues. The model has been developed using aged painting models and then tested to analyze the organic components in samples from the polychrome terracotta Madonna of Citerna by Donatello (1415-1420), where, by GC-MS and FTIR spectroscopy, animal glues and siccative oils were identified. The results obtained are good in terms of both sensibility and specificity of the method. First of all, it was possible to confirm that Donatello used animal glue for the preparation of the painted layers of the Madonna of Citerna and, specifically, glue derived from Bos taurus. Data obtained from sequencing confirm that each sample contains animal glue, revealing that it was mostly prepared from two common European taurine lineages called T2 and T3. There is one remarkable exception represented by one sample which falls into a surviving lineage of the now extinct European aurochs.     

Classification of ancient proteinaceous painting media by the joint use of pattern recognition and factor analysis on GC/MS data

Reference proteinaceous binding media of the kinds historically used in painting (specially prepared for this study) and samples collected from ancient polychrome works of art were analysed by gas chromatography – mass spectrometry. The data have been processed by several multivariate chemometric techniques, such as cluster analysis, principal component analysis, factor analysis and SIMCA technique in order to classify the binding media of the ancient works of art on the basis of the proteinaceous material used. The characterisation of ancient samples was possible by the joint use of SIMCA technique and factor analysis. The latter, in particular, has made it possible to point into evidence the presence of at least two latent factors. The first factor seems to be connected with the chemical composition of the painting media, while the second factor is likely to be connected with ageing processes. Received: 14 October 1998 / Revised: 23 April 1999 / Accepted: 20 May 1999     

Classification of ancient proteinaceous painting media by the joint use of pattern recognition and factor analysis on GC/MS data

Reference proteinaceous binding media of the kinds historically used in painting (specially prepared for this study) and samples collected from ancient polychrome works of art were analysed by gas chromatography – mass spectrometry. The data have been processed by several multivariate chemometric techniques, such as cluster analysis, principal component analysis, factor analysis and SIMCA technique in order to classify the binding media of the ancient works of art on the basis of the proteinaceous material used. The characterisation of ancient samples was possible by the joint use of SIMCA technique and factor analysis. The latter, in particular, has made it possible to point into evidence the presence of at least two latent factors. The first factor seems to be connected with the chemical composition of the painting media, while the second factor is likely to be connected with ageing processes. Received: 14 October 1998 / Revised: 23 April 1999 / Accepted: 20 May 1999     

Stratigraphic analysis of organic materials in wall painting samples using micro-FTIR attenuated total reflectance and a novel sample preparation technique

Wall paintings typically contain low concentrations of organic materials within a largely inorganic matrix and are characterised by their high porosity and long-term exposure to severe environmental conditions. The identification of organic materials within specific paint or plaster layers is challenging and the inherent characteristics of wall painting samples present further complications. Embedding materials (such as epoxy, polyester and acrylic-based resins) used to produce cross-sections often infiltrate porous and leanly bound samples, and compromise the interpretation of Fourier transform infrared attenuated total reflectance (FTIR-ATR) spectra and the qualitative identification of natural organic materials. An alternative method for the preparation of cross-sections of wall painting samples was developed using cyclododecane (C(12)H(24)) as a temporary consolidant and barrier coating to encapsulate the sample, and to provide necessary support to produce a cross-section through microtoming. Impacts of traditional and novel sample preparation techniques on the identification of organic materials with micro-FTIR-ATR were examined for both replica and real wall painting samples.