Aviva Burnstock

The use of microspectrofluorimetry for the characterization of lake pigments

In this paper, the potential of confocal microfluorescence spectroscopy is explored for the characterization of selected red lake pigments and paints based on alizarin, purpurin and eosin (weak, medium and strong emitters). The anthraquinone pigments have been used since ancient times by artists, and eosin lakes were used by impressionist painters. Reconstructions of artists paints based on 19th century recipes are examined. The paints were made using the lake pigments bound in a range of binding media including gum arabic, collagen, a vinyl emulsion and linseed oil. The acquisition of the spectra is rapid, with high spatial resolution and the data reliable and reproducible. Together with full emission spectra, it was possible to acquire well-resolved excitation spectra for purpurin, alizarin and eosin based colors. The present investigation suggests that micro-emission fluorescence can also be used as a semi-quantitative method for madder lake pigments, enabling the determination of purpurin lake ratio in a mixture of purpurin and alizarin, which is important for provenance studies. The data obtained with microfluorescence emission with those acquired with fiber-optic fluorimetry are compared. The spatial resolution used, 8microm, is appropriate for the analysis of individual pigments particles or aggregates in a paint film. Micro-emission molecular fluorescence proved to be a promising analytical tool to identify the presence of selected red lake pigments combined with a range of binding media.

An Investigation of Parameters for the Use of Citrate Solutions for Surface Cleaning Unvarnished Paintings

Abstract This study investigates the surface cleaning of an unvarnished painting using citrate solutions at a range of pH. Cleaning tests followed a similar method to that used for cleaning paintings. The effects of the reagents were examined with light microscopy (LM) and scanning electron microscopy (SEM), and an assay for assessing clearance of residual citrate was carried out using gas chromatography–mass spectrometry (GC-MS). The results are used to evaluate the effects that might be observed when using these cleaning reagents, with the aim of improving risk assessment for surface dirt removal from unvarnished paintings. At low acceleration voltages, SEM allowed detailed examination of paint from the same location before and after sequential cleaning treatments, and the results are interpreted in combination with LM and visual assessment. Paint samples treated with solutions at selected concentrations were assessed by semi-quantitative GC-MS analysis. Clearance of the paint surface with water removed the reagent from the surface, and a detection limit of 1 ng is postulated for the method used.

Analysis of Protein-Based Media Commonly Found in Paintings Using Synchronous Fluorescence Spectroscopy Combined with Multivariate Statistical Analysis

The spectrofluorimetric analysis of protein-based binding media, which are commonly found as painting materials, is based on the detection of emissions from amino acids, as well as fluorescent degradation products that develop with aging. Laser-induced fluorescence spectroscopy, fluorescence excitation emission spectroscopy, and time-resolved fluorescence spectroscopy have all been employed in efforts to discriminate between commonly found proteinaceous binding media, including egg white, egg yolk, milk, and casein, as well as collagen-based glues from rabbit skin, ox bone, parchment, and fish. However, synchronous fluorescence spectroscopy (SFS), a rapid means of recording fluorescence properties of samples, has not been reported for the differentiation between binding media. This work focuses on the analysis of a large set of naturally aged films of different protein-based binding media using SFS with a range of different offsets between excitation and emission monochromators between 30–60 nm. An interpretation of synchronous fluorescence spectra of binding media is presented and is followed by an assessment and classification of a database of recorded spectra using multivariate analysis. Importantly, following SFS analysis of films of binding media, principal component analysis is used to differentiate among all the proteinaceous media considered on the basis of clustering of data. This application is thus a novel and nondestructive means for differentiation between protein-based binding media.

A study of the mechanical and surface properties of oil paint films treated with organic solvents and water

Mechanical and surface properties of paint films treated with organic solvents and water have been investigated using a range of thermomechanical and dielectric techniques together with Fourier transform infrared spectroscopy and scanning electron microscopy. Changes in the nature of the surface after treatment were observed. The effect of water, propan-2-ol and propanone (acetone) immersion for 24 hours, and swabbing for a few minutes, on naturally aged 12 years old samples of lead white/linseed oil and burnt sienna/linseed oil could be measured directly in terms of change in the shear modulus of the paint films together with the accompanying change in the ratio of viscous to elastic components present in each system. Generally, the solvent-treated films became harder and showed reduced viscous components, whereas the water-treated samples became softer. There was a change in the dielectric properties of the leached films which pointed to the polar nature of the leachings. FTIR diffuse reflectance spectra supported this conclusion.ZusammenfassungMittels einer Reihe von thermomechanischen und dielektrischen Verfahren sowie FT-IR-Spektroskopie und Scanning-Elektronenmikroskopie wurden die mechanischen und OberflÄcheneigenschaften von mit organischen Lösungsmitteln und Wasser behandelten Anstrichfilmen untersucht. Nach der Behandlung konnte eine VerÄnderung der OberflÄchenbeschaffenheit beobachtet werden. Der Effekt von 24-stündigem Eintauchen in bzw. paar minütigem Abtupfen mit Wasser, Propan-2-ol und Propanon (Azeton) von natürlich gealterten, 12 Jahre alten Proben von Bleiwei\/Leinöl und gebrannter Sienaerde/Leinöl konnte als Funktion des Schubmodules des Anstrichfilmes gemessen werden, begleitet von einem übergang von viskosen zu elastischen Komponenten in jedem System. Im allgemeinen wurden die lösungsmittelbehandelten Proben hÄrter und wiesen weniger viskose Bestandteile auf, wÄhrend die wasserbehandelten Proben weicher wurden. Es trat auch eine Änderung der dielektrischen Eigenschaften der ausgelaugten Filme auf, was auf den polaren Charakter des Auslaugungsvorganges hinweist. FT-IR Remissionsspektren bekrÄftigten diese Schlu\folgerung.

Water Sensitive Oil Paints in the Twentieth Century: A Study of the Distribution of Water-Soluble Degradation Products in Modern Oil Paint Films

Water sensitivity has been observed on unvarnished, twentieth century oil paintings, which presents issues for surface cleaning. Previous studies have shown that manufacturers’ formulations are contributing to one of the known causes of water sensitivity: magnesium sulphate heptahydrate formation. It has been proposed that the formation of this water soluble degradation product is a result of interactions between the paint additive magnesium carbonate with environmental sulphur dioxide at elevated relative humidity. The present study examined the presence of this water soluble degradation product on the surface and in the bulk paint films of naturally aged Winsor & Newton paint swatches made from the 1940s to the 1990s. Scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX) was the primary method for detection. Heptahydrate crystalline entities on the surface were found to be below the detection limit for X-ray diffraction (XRD). Water immersion tests suggested that water sensitivity due to magnesium sulphate heptahydrate formation is largely a surface phenomenon. Painting case studies helped to contextualise the problem in light of future conservation treatments for water sensitive paintings.

Twentieth Century Oil Paint. The Interface Between Science and Conservation and the Challenges for Modern Oil Paint Research

This chapter introduces recent research related to aspects of the deterioration of modern paintings in oil media. The research was informed by collaboration between conservators and scientists and utilises phenomenological and experimental methodologies to investigate the causes of optical changes in paint, such as efflorescence and salt formation, and the sensitivity to water that occurs on surface cleaning some unvarnished oil paintings. Examples are given of results based on case studies of paintings and the results of systematic experimental investigation of paint samples, including those supplied by manufacturers and reconstructions based on paint formulations. Results of this research are given including the cause of water sensitivity related to the formation of magnesium sulphate hydrate in selected manufactured oil paints, and criteria for further investigation of the phenomena in other paints. Contributions in this volume that address other classes of material deterioration including the formation of metal soap crusts and treatment approaches are introduced.

An Investigation into the Viability of Removal of Lead Soap Efflorescence from Contemporary Oil Paintings

Metal soap efflorescent hazes and crusts are one of the most visually disturbing of all metal soap related alterations in paintings. The phenomenon presents particular challenges for conservators as the surface deposits that form are insoluble and intimately bound with the paint film. The superficial deposits accumulate following migration of metal carboxylates, a product formed within the paint film from reaction of free fatty acids with metal ions from pigments and/or driers. Upon deposition at the surface, the metal carboxylates undergo a process of remineralisation, the products of which are determined by the atmospheric conditions that the painting is exposed to. The material can appear optically similar to the whitish haze of organic efflorescence though manifestations also range from crystalline clusters to thick crusts, and in some cases the painting may consequently be rendered partially unreadable. This study aimed to investigate the removal of visually disturbing lead soap efflorescence with Ethylenediaminetetraacetic acid (EDTA), which sequesters the lead ions from the remineralised crust. Through a careful balance of variables such as pH, concentration and application, it is feasible to thin the superficial material significantly. By this means it is possible to saturate the surface of the paint film and render the previously disfiguring efflorescence transparent. Paintings previously treated with this method show no signs of recurrence and thus it appears to be a viable, long-term treatment option.

Scanning electron microscopy techniques for imaging materials from paintings.

ABSTRACT This chapter reviews a range of techniques of scanning electron microscopy (SEM) and its application to the study of paintings and artists materials. The review focuses on imaging the materials (rather than chemical analysis), and its application to the materials used for and from easel paintings. Examples of published experimental studies of cleaning, paint surface defects, bio-deterioration of painting materials from the conservation and paint manufacturers literature are discussed, with reference to sample preparation and imaging conditions. Images of selected artists materials and materials from paintings examined using conventional high vacuum SEM, low vacuum (variable pressure) SEM and ESEM are given to illustrate comparative techniques.

WITH PAINT FROM CLAUS & FRITZ: A STUDY OF AN AMSTERDAM PAINTING MATERIALS FIRM (1841–1931)

poraneous artists, the range of materials it supplied, and the quality controls it applied to its products. Claus & Fritz manufactured a range of its own oilbased paints, supplied in tin tubes. Analysis of the inorganic pigments and binding media of 41 different paints from its 1921 line was carried out in this study. The results of the analysis characterize the range of pigments and mixtures used, including extenders, and the use of additives such as beeswax and resin to the

Colour Change in Sample - Reconstructions of Vincent van Gogh's Grounds due to Wax-Resin Lining

Abstract This study examined the visual impact (colour change) of wax-resin lining on sample reconstructions of Vincent van Gogs grounds, made as part of the Historically Accurate Oil Painting Reconstruction Techniques (HART) Project. The lining method followed that used by J.C. Traas for lining paintings by Van Gogh between 1926 and 1933. Visual changes in the ground samples after living were noted and colour change was measured using a reflectance spectrophotometer. The binding medium of the ground was found to be the most significant factor, with the greatest darkening occurring in samples bound in glue, followed by emulsion and oil. The presence and the method of application of size used in the preparation of the ground samples and the inorganic composition also influenced darkening and colour change as a result of lining. Grounds on unsized canvas darkened the most, while a layer of gelled size reduced impregnation with the lining adhesive and concomitant darkening. Chalk-containing grounds darkened more than grounds containing barium sulphate or lead white. Comparisons between the reconstruction samples and wax-resin lined paintings by Van Gogh highlighted difficulties in attributing the darkening of the ground in the paintings to the lining or to other factors, such as staining by original oil binder in the paint.