Study of the microbiodegradation of terpenoid resin-based varnishes from easel painting using pyrolysis–gas chromatography–mass spectrometry and gas chromatography–mass spectrometry

The alterations produced by microbiological attack on terpenoid resin-based varnishes from panel and canvas paintings have been evaluated using pyrolysis–gas chromatography–mass spectrometry (Py–GC–MS) and gas chromatography–mass spectrometry (GC–MS). The proposed methods include the on-line derivatisation of drying oils and diterpenoid resins using hexamethyldisilazane during pyrolysis and the application of methyl chloroformate as a derivatisation reagent for triterpenoid resins in GC–MS. Two types of specimens, consisting of model oil medium prepared from linseed oil and model spirit varnishes prepared from colophony and mastic resins dissolved in turpentine, have been used as reference materials. For a series of specimens upon which different genera of bacteria and fungi were inoculated and encouraged to grow, analyses indicated that no mechanisms that commonly occur during the attack of enzymes on drying oils and terpenoid biodegraders were observed to occur in the oil medium and varnishes studied. Thus, the degradation pathways observed in the performed trials usually occur as consequence of natural ageing. Specific trials consisting of the application of biocides to uninoculated colophony varnish resulted in the identification of processes that produce undesirable degradation of the varnish due to interactions between the biocide and the varnish components. Finally, the studied biocides—Biotin, New-Des and Nipagine—generally exhibited good inhibiting effects on the microorganisms studied, although some interesting differences were found between them regarding the application method and type of biocide.     

Excitation emission and time-resolved fluorescence spectroscopy of selected varnishes used in historical musical instruments

The analysis of various varnishes from different origins, which are commonly found on historical musical instruments was carried out for the first time with both fluorescence excitation emission spectroscopy and laser-induced time-resolved fluorescence spectroscopy. Samples studied include varnishes prepared using shellac, and selected diterpenoid and triterpenoid resins from plants, and mixtures of these materials. Fluorescence excitation emission spectra have been collected from films of naturally aged varnishes. In parallel, time-resolved fluorescence spectroscopy of varnishes provides means for discriminating between short- (less than 2.0 ns) and long-lived (greater than 7.5 ns) fluorescence emissions in each of these complex materials. Results suggest that complementary use of the two non destructive techniques allows a better understanding of the main fluorophores responsible for the emission in shellac, and further provides means for distinguishing the main classes of other varnishes based on differences in fluorescence lifetime behaviour. Spectrofluorimetric data and time resolved spectra presented here may form the basis for the interpretation of results from future in situ fluorescence examination and time resolved fluorescence imaging of varnished musical instruments.     

Application of ATR-far-infrared spectroscopy to the analysis of natural resins

This study proposes FTIR spectroscopy in the far-infrared region (FarIR) as an alternative method for the characterisation of natural resins. To this purpose, standards of natural resins belonging to four different categories (sesquiterpenic, i.e. elemi, shellac; diterpenic, i.e. colophony, Venice turpentine; diterpenic with polymerised components, i.e. copal, sandarac; triterpenic, i.e. mastic and dammar) used as paint varnishes have been analysed by FarIR spectroscopy in ATR mode. Discrimination between spectral data and repeatability of measurements have been magnified and verified using principal component analysis, in order to verify the effectiveness of the method in distinguishing the four resin categories. The same samples were analysed in the MidIR range, but the spectral differences between the different categories were not evident. Moreover, the method has been tested on historical samples from the painting “La Battaglia di Cialdiran” (sixteenth century) and from a gilded leather (seventeenth century). In the first case, FarIR spectroscopy allowed confirmation of the results obtained by analytical pyrolysis. In the latter, FarIR spectroscopy proved successfully, effective in the identification of the superficial resin layer that could not be detected with the bulk chromatographic analyses.     

Characterization of bile acids and fatty acids from ox bile in oil paintings by gas chromatography-mass spectrometry

Characterization of ox bile, traditionally used in painting, is of interest in the fields of archaeometry and conservation and restoration of works of art. Bile acids, fatty acids (F), and cholesterol found in ox bile have been identified using a derivatization method that combines the formation of ethyl esters from the carboxylic groups and the trimethylsilyl ethers from hydroxyl groups. This method of analysis is consistent with these others proposed by the authors to analyze drying oils, proteins, and diterpenic resins usually used as binders and varnishes by the painters. Bile acids from binary samples such as animal glue/ox bile, casein/ox bile and Arabic gum/ox bile have been successfully analyzed using the proposed method. Finally, a method of analysis of mixtures of drying oil and ox bile has been also proposed attempting to quantitatively characterize samples in which ox bile was added to the drying oil for increasing the surfactant properties.     

Mass spectrometric techniques for characterizing low-molecular-weight resins used as paint varnishes

The molecular structure of three low-molecular-weight resins used as paint varnishes has been characterized by use of an approach based on three different mass spectrometric techniques. We investigated the ketone resin MS2A, the aldehyde resin Laropal A81, and the hydrocarbon resin Regalrez 1094, now commonly used in restoration. To date, the molecular structures of these resins have not been completely elucidated. To improve current knowledge of the chemical composition of these materials, information obtained by gas chromatography–mass spectrometry (GC/MS), pyrolysis–gas chromatography–mass spectrometry (Py/GC/MS), and electrospray ionization mass spectrometry (ESI–Q–ToF) was combined. Analysis, in solution, of the whole polymeric fraction of the resins by flow-injection ESI–Q–ToF, and of the non-polymeric fraction by GC–MS, enabled us to identify previously unreported features of the polymer structures. In addition, the Py–GC/MS profiles that we obtained will help to enhance the databases currently available in the literature. The proposed approach can be extended to other low-molecular-weight resins used as varnishes in conservation.     

Study of the influencing effect of pigments on the photoageing of terpenoid resins used as pictorial media

Terpenoid resins have been mainly used as components of pictorial varnishes and binding media from ancient times. In such latest instances, the resin is mixed with pigments affecting its physical and chemical properties. A new procedure based on gas chromatography-mass spectrometry (GC/MS) has been applied, in this work, in combination with Fourier transform infrared spectroscopy (FTIR), with the aim of determining the changes undergone by di- and triterpenoid resins employed as components of binding media. The GC/MS method is based on the derivatisation of these resins using trimethylsilylimidazol. Characterization of the main components of the di- and triterpenoid fractions and their oxidised products, occurring in the diterpenoid resin colophony and a triterpenoid Mexical copal (Bursera cuneata (Schl) Engl.), has been achieved. Artificially photoaged specimens of pure resin and binary systems pigment+resin prepared as thin films using lead white, ochre yellow, umber raw and verdigris have also been analysed to study the changes undergone by the di- and triterpenoid components of the resins. Oxidation processes taking place on di- and triterpenoids during photoageing are described. Moreover, the results obtained indicate that pigments have a different effect on the two studied resins. Thus, the presence of pigments induces, in general, a catalysing effect on the oxidative polymerisation reactions in the earliest stages of the natural curing of the paint films whereas a loss of the catalysing effectiveness, in particular, for verdigris containing specimens, is observed during photoageing. Complexation of diterpenoid molecules with copper(II) ions in the earliest stages of the curing has also been evidenced by FTIR analysis.     

Characterization of acrylic resins used for restoration of artworks by pyrolysis-silylation-gas chromatography/mass spectrometry with hexamethyldisilazane

A procedure based on the technique of the pyrolysis-GC/MS has been applied, in this work, in order to determine the composition of synthetic acrylic resins employed in artworks. The method is based on the on line derivatization of these resins using hexamethyldisilazane (HMDS). Results obtained have been compared with those others from direct pyrolysis and in situ thermally assisted hydrolysis and methylation with tetramethylammonium hydroxide (TMAH). Sensitivity using HMDS as derivatising reagent is found similar to that from direct pyrolysis and methylation with TMAH. Better resolution of the most representative peaks has been also obtained. Additionally, this method reduces the formation of free acrylic acid molecules during the pyrolysis process and, in consequence, more simplified and well-resolved chromatograms are obtained. Finally, the reported procedure has been successfully used for characterizing several acrylic-based varnishes and binding media currently used in Fine Arts and real pictorial samples from graffiti performed on a Middle Ages bridge.     

Adhesives and coatings from phenol-formaldehyde/resorcinol-formaldehyde resins

Resole phenol-formaldehyde resins were prepared and modified with the prepared resorcinol-formaldehyde resins. The optimum conditions of formulation and curing processes were studied to obtain modified wood adhesives characterized by high-tensile shear strength values. This study indicated that the more suitable conditions are equal weight ratios of phenol-formaldehyde to resorcinol-formaldehyde resins in the presence of paraformaldehyde (10 or 15 wt%) of the resin content as a curing agent at 80 or 25°C for 40 min or 100–110 days, respectively. The activation energies of the curing reactions for phenol-formaldehyde/resorcinol-formaldehyde resin samples were determined. Metallic and glass coatings from the previous pure resins and their formulated cured mixtures were prepared and evaluated as varnishes or paints. Copyright © 1998 John Wiley & Sons, Ltd.     

Artificial Photoaging of Triterpenes Studied by Graphite‐Assisted Laser Desorption/Ionization Mass Spectrometry

Seven triterpenes were selected for study of their photoaging behavior by graphite‐assisted laser‐desorption/ionization mass spectrometry as the primary analytical tool. The triterpenes serve as simplified reference systems for complex triterpenoid resins, which are used as varnishes on paintings. Some of the triterpenes are main components of such natural resins; others were chosen for their particular functional groups or carbon skeleton to evaluate specific influences on the aging process. Progressive aging resulted in incorporation of oxygen and simultaneous loss of hydrogen, recognizable in the mass spectra by the appearance of signals with mass increments of 14 and 16 Da. Degradation of aging products also led to compounds with lower masses than the initial triterpenes. The general aging behavior of the triterpenes studied was found to be rather similar, although differences in reactivity, and, therefore, in the extent of oxidation were found, depending on the functional groups. Compounds with aliphatic ketone groups were much more reactive under the test conditions than others. A mixture of five triterpenes showed the highest reactivity. Yellowing, an important aspect of aging with regard to varnishes on paintings, was found to be related to a general breakdown of the initial triterpenes and was not caused by a single compound.     

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.     

Adhesives and coatings based on phenolic/epoxy resins

Low molecular weight epoxy resin based on bis (4‐hydroxy phenyl) 1,1 cyclohexane was prepared and modified with various types of the prepared phenolic resins. Phenol–, cresol–, resorcinol–and salicylic acid–formaldehyde resins were used. The optimum conditions of formulation and curing process were studied to obtain modified wood adhesives characterized by high tensile shear strength values. This study indicated that the more suitable conditions are 1:2 weight ratio of phenol–or cresol–formaldehyde to epoxy resin in the presence of phthalic anhydride (20 wt%) of the resin content as a curing agent at 150°C for 80 min. Resorcinol–or salicylic acid–formaldehyde/epoxy resins formulated at 1:2 weight ratio were cured in the presence of paraformaldehyde (20 wt%) at 150°C for 60 min. The effect of the structure of phenolic resins on the tensile shear strength values of formulated resin samples, when mixed with the epoxy resins and cured under the previously mentioned optimum conditions for different times, was investigated. Metallic and glass coatings from the previous resins were also prepared and evaluated as varnishes or paints. Copyright © 1999 John Wiley & Sons, Ltd.     

Spatially resolved element analysis of historical violin varnishes by use of μPIXE

External μPIXE has been used for characterisation of small samples of varnish from historical violins, and pieces of varnished wood from historical and modern stringed instruments. To obtain spatially resolved information about the distribution of elements across the varnish layers single-spot analysis, line-scans, and area-mapping were performed. Local resolution of approximately 20 μm was obtained from the 3 MeV, 1 nA proton micro-probe. Results from simultaneous multi-element determination of Na, Mg, Al, Si, P, S, K, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Br, Rb, Sr, Ag, Cd, Sn, Ba, and Pb in historical varnishes are presented. Semi-quantitative evaluation of line-scans recorded on diverse historical varnishes is reported. The applied method is discussed in detail and the results obtained are critically reviewed and compared with those in the literature.      

Characterisation of varnishes used in violins by pyrolysis-gas chromatography/mass spectrometry

The correct characterisation and a detailed knowledge of the materials originally used in violin varnishes, like natural resins, is crucial for the conservation in museums and for a suitable restoration technique. The study presented here reports on the potential of pyrolysis (Py) coupled with gas chromatography (GC) and mass spectrometry (MS) for the identification of chemical markers of each resin; this technique is very sensitive and selective, it needs a small quantity of sample and does not require chemical treatments. To improve the chromatographic behaviour of polar compounds the derivatising agent tetramethylammonium hydroxide (TMAH) in combination with pyrolysis has been used, in the so-called TMAH thermochemolysis or thermally assisted hydrolysis and methylation (THM), or more simply pyrolysis-methylation. The natural resins studied were colophony, sandarac, manila copal, elemi, amber and benzoin, mainly composed of terpenic compounds, with the exception of the latter, composed of aromatic compounds. Many compounds were identified; in particular, methyl esters of resinous acids that, individually or in a group, can be used as chemical markers. However, through this technique it was not possible to distinguish between the sandarac and manila copal resins because their chromatographic behaviour is very similar. Finally, the procedure applied has been employed in the characterisation of original varnish samples.     

Dewatering of crude oil emulsions 2. Interfacial properties of the asphaltic constituents of crude oil

The importance of the interfacial rheology in determining the stability of water-in-Buchan crude oil emulsions has been demonstrated in part 1 of this series of papers (R.A. Mohammed, A.I. Bailey, P.F. Luckham and S.E. Taylor, Colloids Surfaces A: Physicochem. Eng. Aspects, 80(1993)223). In part 2, interfacial tensions of crude oil, and solutions of asphaltenes and resins in a model oil have been investigated. Surface pressure vs. area (Π—A) curves of monolayers of asphaltenes, resins and their mixtures have been established. In its dependence on the ratio of resins to asphaltenes, the pseudostatic dilatational modulus has high values for low resin-to-asphaltene ratios and low values for high resin-to-asphaltene ratios. This is expected to throw light on the cause of the enhanced stability of water-in-crude oil emulsions.     

Use of NIR spectroscopy in the production of modified industrial resins

Natural resins are scarcely used, but after appropriate modification processes they acquire characteristics of viscosity, point of softening, stability, etc. that facilitate their application in fields such as paintings, varnishes, cosmetic, etc. The complexity of resins makes it very difficult to monitor the reactions involved in their modification, the extent of which is usually determined via more experimentally accessible parameters. However, the methods typically used to determine such parameters are slow and produce environmentally unfriendly waste.In this work, we assessed the potential of NIR spectroscopy, as an alternative to the traditional analytical methods, for monitoring the industrial processes involved in the production of modified resins. To this end, we developed PLS calibration models that were used to quantify physical (viscosity and cloud point) and chemical parameters (acid and hydroxyl numbers), with a view to characterize the evolution of the resins during the reaction that take place throughout the fabrication process.Samples were withdrawn at different times stages of the process for analysis with the proposed quantitation models; the data thus obtained were compared with those provided by reference methods. Based on the results, NIR spectroscopy is an effective choice for the accurate, expeditious monitoring of industrial resin modification processes.     

Performance of methylphenyl hydrogen-containing silicone oils for LED encapsulation

Three-dimensional light-emitting diodes (LEDs) are the preferred light source for bulb lamps due to their 360° illumination. Addition curing silicone resins have usually been used to encapsulate LEDs. LED-filament encapsulation needs silicone resins having high thermal performance and thixotropy. Herein, a low refractive index and highly anti-thermal aging silicone oil was synthesized by hydrolysis and co-condensation method, and used to prepare an encapsulation material for high-power LED-filament. The cured silicone materials were characterized by thermogravimetric analysis (TGA) and thermal aging test under 180°C and 250°C. The results demonstrated that the thermal stability of the cured silicone resins with short-chain phenyl silicone as a crosslinker was higher than that with long-chain methyl silicone oil crosslinker. Owing to the excellent thermal stability, appropriate hardness, high transparency and photoelectric efficiency, this LED encapsulation material is a promising candidate for high-power LED package.     

Synthesis of high oil‐absorption resins of poly(methyl methacrylate‐butyl methacrylate) by suspended emulsion polymerization

The synthesis of high oil‐absorption resins by suspended emulsion polymerization process for the first time with butyl methacrylate (BMA) and short‐chain methyl methacrylate (MMA) as the monomers was studied. And the effects of different polymerization technological parameters, such as the comonomer, initiator, crosslinker, emulsifier, dispersant agent, and the agitation rate, on the oil absorbency of high oil‐absorption resins were discussed in detail. The optimum polymerization conditions were obtained. With the increasing contents of these factors, the oil absorbency increased first, and then decreased. The highest oil absorbency to toluene was 17.6 g/g. The particle morphology of the high oil‐absorption resins was observed by scanning electron microscopy (SEM). The resins were determined by FTIR spectrometry. Compared with the high oil‐absorption resins prepared by suspension polymerization process and emulsion polymerization process, the high oil‐absorption resins prepared by suspended emulsion polymerization process had the higher oil absorbency, faster oil‐adsorbing rate, better oil‐retention, and regeneration property. Copyright © 2010 John Wiley & Sons, Ltd.     

Analytical characterization of diterpenoid resins present in pictorial varnishes using pyrolysis-gas chromatography-mass spectrometry with on line trimethylsilylation

A procedure based on the technique of the pyrolysis-gas chromatography-mass spectrometry (Py-GC-MS) has been applied, in this work, in order to determine the composition of diterpenoid resin employed in art works. The method is based on the on line derivatization of these resins using hexamethyldisilazane (HMDS). Results obtained were compared with those previously reported in literature from Venice turpentine, Strasbourg turpentine, colophony, sandarac and Manila copal using this same method and with those others from in situ thermally assisted hydrolysis and methylation with tetramethylammonium hydroxide (TMAH). Canada balsam, copper resinate and Copaiba balsam have been also analyzed extending the scope of this method in the field of the analysis of artwork materials. Several non-reported trimethylsilylated derivatives of compounds present in the diterpenoid resins have been identified. An improvement in sensitivity has been obtained by using HMDS as derivatizing reagent, together with a better resolution of the most representative peaks. Additionally, this method reduces the number of pyrolytic fragmentation, recombination, dehydration and isomerization products formed during the pyrolysis process and, in consequence, more simplified chromatograms are obtained. Finally, the reported procedure has been successfully used for characterizing two diterpenoid resin-based varnishes present in the canvas painting "The Betrothal of the Virgin" (Anonymous, 17th century) which is included in the pictorial collection of Saint Joseph Church in Taormina (Italy) and the Magdalena Tryptich (Master of Alzira, 16th century, Valencia, Spain).     

Study of ageing of ketone resins used as picture varnishes by pyrolysis–silylation–gas chromatography–mass spectrometry

This contribution presents a research aimed at the study of the commercial products Laropal K80, Keton N and MS2A, ascribed to ketone resins prepared as thin films, in an attempt to reproduce the pictorial layers and protective finishes that are commonplace in contemporary paintings. For this purpose, a new method based on “online” silylation–pyrolysis using hexamethyldisilazane as a derivatisation reagent in pyrolysis–gas chromatography–mass spectrometry (Py–GC–MS) has been proposed. This procedure leads to the unambiguous identification of such varnishes and improves direct Py–GC–MS. Chemical changes due to the degradation effect of environmental agents have been especially considered. To that end, three different accelerated ageing processes were applied to a series of specimens prepared from the studied commercial products: thermal, UV light and ageing in an SO₂-polluted chamber. Chemical changes due to UV light ageing of Keton N resin are in good agreement with those previously reported in the literature.     

Modified coatings based on chlorosulfonated polyethylene

The results of investigations of the effect of solid petroleum resins, epoxide oligomers, and type of curing agent upon the properties of varnishes and coatings based on chlorosulfonated polyethylene are given. It is shown that the use of cycloaliphatic isocyanates and amine-containing organic silicon compounds allows one to obtain coatings with a complex of high processing and operating characteristics.