Showing papers in "Studies in Conservation in 1998"

Studies of lead corrosion in acetic acid environments

Abstract: Many lead artifacts are danzaged after being kept for a short period in enclosures that contain materials which emit carboxylic acids. The formation of corrosion products and the corrosion sensitivity of lead were studied under experimental conditions in which the duration of exposure, the acetic acid (ethanoic acid) concentration and the relative humidity (RH) were varied. At 54% RH, in the acetic acid concentration range studied, weight gain was maximun at around 4mgm−3. Over a period of 12 months, with RH levels below 75%, no damage was detected on lead samples at acetic acid concentrations below 0·43mgm−3. However, variations in the composition and morphology of lead as well as the presence of other carbonyl compounds in enclosures may affect the rate of corrosion. For these reasons, a total concentration of low molecular weight carbonyl compounds no higher than 0·1mgm−3 is recommended. Strategies to maintain the concentration of carbonyl compounds below 0·1mgm−3 are proposed.

Comparative chromatographic and mass-spectrometric studies of triterpenoid varnishes: fresh material and aged samples from paintings

Abstract: Summary-The triterpenoid resins dammar and mastic are frequently used as varnishes for paintings. Unfortunately, these varnishes degrade in the course of time. A large number of aged yellowed varnishes taken from paintings from several museum collections were analyzed by gas chromatography/mass spectrometry (GCMS) to identify oxidized triterpenoids, which are formed during natural aging processes. Discrimination between the different types of aged varnishes was achieved by direct temperature-resolved mass spectrometry (DTMS). GCMS further showed that the triterpenoid fraction strongly decreases during aging. It is likely

Characterization of proteinaceous binders in wall painting samples by microwave-assisted acid hydrolysis and GC-MS determination of amino acids

Abstract: An analytical procedure for the characterization of proteinaceous binders (milk or casein, egg and animal glue) in artistic wall painting samples is described. The method is based on microwave-assisted acid hydrolysis of the sample, and on derivatization of the amino acids freed with a silylating agent and their quantitative determination by gas chromatography/mass spectrometry. The procedure was tested on wall painting reference samples, and showed a typical protein recovery of about 70% at 0·1mg sample size. Fourteen amino acids were determined and some ratios between their concentrations were selected, so that the proteinaceous binders in the sample could be identified. Results on some samples from frescoes from the Monumental Celnetery in Pisa (Italy) showed that the amino acid composition of casein differed significantly from that expected, as a result of degradation processes due to aging and moisture.

Green degradation products of azurite in wall paintings: identification and conservation treatment

Abstract: After the restoration of the fourteenth- to fifteenth-century wall painting of San Antonio Abate in the church of San Pietro at Quaracchi near Florence, using the well-known treatment involving application of ammonium carbonate followed by barium hydroxide, a small region of the green degradation products of azurite changed colour to a dark blue. After two years, this blue had again changed colour, showing that the conservation procedure could cause chemical alterations, and that it had produced an unstable material. This study investigated the chemistry of these phenomena, in order to determine whether a conservation procedure based on the application of ammonium carbonate and barium hydroxide is suitable and appropriate in the presence of certain green degradation products of azurite. Fourier transform infrared spectroscopy (FTIR) and X-ray diffractometry (XRD) showed that the main green degradation product was not malachite but paratacamite, a basic copper chloride which forms when there is a s...

The ‘Portail de la Mere Dieu’ of Amiens cathedral: its polychromy and conservation

Abstract: Numerous studies and two recent conferences have been devoted to the application of laser technology to art conservation. The so-called ‘POrtail de la Mere Dieu’ of the cathedral of Amiens (Somme) has become the first major sculptural ensemble to have cleaning by Nd: YAG laser incorporated in its conservation programme (1993-96). The recent work has revealed polychromy which is relnarkably intact. Extensive historical and scientific research was undertaken prior to Commencement of work, and continuous dialogue between conservators, the architect, inspectors, laser engineers and conservation scientists led to a flexible, mixed approach to the implelnentation of laser cleaning, taking account of its strengths and weaknesses.

GC-MS and SEM studies on the effects of solvent cleaning on old master paintings from the National Gallery, London

Abstract: This paper adopts a new approach to cleaning research, made possible by recent developments in sample derivatization. For the first time, an extensive analytical study has been made of the solvent cleaning of a range of paintings from the early fifteenth century to the end of the nineteenth century. Direct analytical comparisons are made between samples from mechanically and solvent-cleaned test areas of both tempera and oil paintings, using gas chromatography-mass spectrometry (GC-MS) and scanning electron microscopy (SEM).

A history of conservation

Abstract: L'auteur de cet article presente un historique de la conservation des objets (antiquites et beaux-arts) et des monuments en Grande-Bretagne depuis la Premiere Guerre Mondiale, evoquant egalement le role de H. J. Plenderleith a la direction du centre ICCROM, a Rome, en collaboration avec le gouvernement italien.

Application of nuclear magnetic resonance spectroscopy to the analysis of organic archaeological materials

Abstract: The application of nuclear magnetic resonance (NMR) spectroscopy to the analysis of organic archaeological materials can provide valuable information to conservation scientists, conservators and archaeologists. In this review the usefulness of the NMR technique and the breadth of possible applications are illustrated. The technique and its scope are briefly described. Details of the use of NMR spectroscopy to identify the nature and composition of organic residues, to aid in determining the provenance of such residues and its application to the analysis and determination of the extent of degradation of archaeological materials are presented.

A new lead-based yellow in the seventeenth century

Abstract: Since the important rediscovery by Jacobi in 1941 of the use of lead-tin yellow as a traditional artists' pigment, and the identification by Kuhn of two distinct modifications of this material, elemental analysis and crystallographic determinations using X-ray diffraction (XRD) have been applied routinely to opaque yellow pigments from Old Master paintings. We report here the discovery and characterization by these methods of a new lead-based yellow in seventeenth-century paintings, based on a ternary oxide of lead, tin and antimony. This pigment is distinct from the two varieties of lead-tin yellow and from pure lead antimonate (Naples yellow); it appears to be restricted in use to Italian painting and specifically to paintings produced in Rome. Examples in the work of Poussin, Pietro da Cortona, Salvator Rosa, Sassoferrato, Gentileschi and Lanfranco are given, and art-historical interpretations based in the presence of this pigment are discussed.

Thermodynamic characterization of skin, hide and similar materials composed of fibrous collagen

Abstract: Differential scanning calorimetry (DSC) and equilibriwn thermodynamics were applied to untanned, brain-tanned and smoke-tanned fibrous collagen in the development of quantitative methods to characterize deterioration in museum materials composed of mammalian skin and hide. Changes characteristic of deterioration were recorded for the equilibrium temperature and the calorimetric enthalpy and entropy functions associated with the denaturation, i.e., hydrothermal shrinkage, of the native, fibrous structure of collagen. Gibbs energy curves were used to determine the overall loss of structural stability at telnperatures below the hydrothermal shrinkage temperature. Collagen denaturation produced two partly overlapping endothermic peaks in the DSC thermograms. Study of whole endotherms and the two individual peaks after separation by multiple least-squares curve-fitting revealed that crosslink concentration distinguishes the two types of collagen represented by the peaks and influences the stability of ...

Gilded stuccoes of the Italian baroque

Abstract: The stucco decorations in the church of San Ambrogio, Cantu (Como, Italy) date to the baroque and represent an important example of decorative schemes in Lombardy. Gold leaf was originally applied to a ‘finishing mortar’, composed essentially of calcic lime and marble fragments. Examination of gilded fragments by X-ray photoelectron spectroscopy (XPS), scanning electron microscopy and X-ray analysis (SEM-EDX), Fourier transform infrared spectroscopy (FTIR) and micro-Raman spectroscopy established that under the gold leaf (which was up to 5μm thick), a layer composed of lead oxides (PbO, Pb3O4) and lead sulphate (PbSO4) was present. Gas-chromatographic/mass-spectrometric analysis (GC/MS) revealed that linseed oil was used in the mordant for the gilding. It seems that the gold leaf was applied using linseed oil as a mordant (fixing agent) and litharge as a dryer and/or inert pigment. Where the gold leaf had become detached, the orange-red surface was covered with a lime painting, scialbo, which cont...

Cleaning of daguerreotypes with an excimer laser

Abstract: The cleaning of daguerreotypes is a process that must remove tarnish layers and debris without altering the optical properties of the daguerreotype. This means that (1) the polished silver layer substrate must not be etched or pitted and (2) the image particles must not be altered or damaged. Electro cleaning is the only known method of cleaning gilded daguerreotypes; however, it is not suitable for the treatlnent of ungilded and coloured daguerreotypes. This article describes a new laser method for cleaning daguerreotypes. A model is developed for the cleaning process and testing procedures are discussed. This method permits (1) the cleaning of gilded and ungilded plates, (2) local treatment and (3) removal of tarnish without immersion in solvents and chemicals.

The social and historic construction of professional values in conservation

Abstract: This paper discusses the social history of the emergence of conservation as a profession distinct from traditional restoration. It proposes that the development of conservation as a distinct field came about thrpough the evolution of an existing area of practice, in a changing conceptual climate which increasingly acknowledged the necessity for, and the legitimacy of, the scientific model. This paper considers the changes in societal values that led conservators to hold their present ethical principles, values and beliefs, focusing on two in particular: the importance of preserving the integrity of the object, and the belief that the best way to do this is through the application of science.

Epoxy resin-consolidated stone: appearance change on aging

Abstract: Dilute solutions of epoxy resins have been used successfully in the past to consolidate deteriorated, porous stone. However, the appearance change (darkening, yellowing) on curing has proved to be a deterrent to the wider use of these materials by conservators. In the study reported here, it is shown that solvent washing to remove surface-deposited resin and exposure to sunlight are effective methods for restoring the original visual appearance of consolidated outdoor stone.

The development of painting on coloured surfaces in sixteenth-century Italy

Abstract: Paint samples from nearly 140 sixteenth-century Italian panels and canvases in the National Gallery, London, have been examined to determine the nature of their preparatory layers. The results are presented in tables organized by colour. These tables are subdivided into three geographical regions, roughly equivalent to the established art-historical division into the Florentine and Roman, the North Italian and the Venetian Schools. By organizing the results in this way, it is possible to distinguish patterns of development and usage. These appear to contradict many traditional assumptions about the introduction of painting on coloured surfaces.

Moche wallpainting pigments from La Mina, Jequetepeque, Peru

Abstract: Some fragments of polychrome wall paintings from the first century AD Moche site of La Mina in the Jequetepeque Valley, Peru, were studied to identify the nature of the pigments employed by the early Moche artists. The colorants identified were chrysocolla for a pale green, calcite for white and charcoal for black; light grey-blue was shown to be an 'optical blue' composed of finely ground charcoal and calcite. Reds were red ochre, yellow was probably yellow ochre, and pink was a mixture of calcite and red ochre. The occurrence of an 'optical blue' in ancient Latin-American tomb paintings shows that the use of this pigment mixture of black and white to create a blue was not confined to Europe and the Old World.

Gas-chromatography/mass-spectrometry of works of art: characterization of binding media in post-Byzantine icons

Abstract: The painting techniques used in four post-Byzantine icons (dated between 1600 and 1700) have been studied A gas-chromatographic/mass-spectrometric method was applied to characterize the binding media of the different layers of the polychromy Samples taken from the different paint layers were analysed after hydrolysis and derivatization The data indicate that the binding medium used for the paint layer may be an emulsion of egg and walnut oil, while egg can be regarded as the binding medium used primarily for the bole Animal glue is very likely the binder used for the ground

Fourier transform-raman spectroscopy of ivory : A non-destructive diagnostic technique

Abstract: The Fourier transform-Raman spectra of elephant ivory are reported and the application of the technique to the non-destructive diagnostic analysis of ivory tusks and artifacts is evaluated. Characteristic vibrational features are identified which distinguish genuine elephant ivory from teeth and bone. An important outcome of this investigation is the ability of vibrational Raman spectroscopy to characterize specimens of ivory from African (Loxodonta africana) and Asian (Elephas maximus) elephants and also fronl the extinct proboscid woolly mammoth. Remote sensing applications for larger samples and for inlaid material are also proposed.

Electrochemical tests as alternatives to current methods for assessing effects of exhibition materials on metal artifacts

Abstract: Summary-Many materials used in the storage and display of musewn objects are potentially corrosive and should not be used in the vicinity of specific metals. The fOddy test' is the procedure used in most musewns to assess the suitability of such lnaterials. However, there have been reports in the literature of problems with reproducibility and tinze constraints. In manufacturing industries, where sbnilar problems have been encountered, electrochemical testing has replaced tests based on visual asseSSlnent. Experiments with electrochemical testing are reported here, using typical exhibition and storage materials in conjunction with lead, copper and silver coupons. The results suggest that the polarization resistance test has potential for rapidly and objectively identifying possibly dmnaging materials. This method provides a quantitative measure of corrosion rate in milli-inches per year for a specific metal used in conjunction with a particular lnaterial.

Contribution to the study of grounds for panel painting of the Spanish School in the fifteenth and sixteenth centuries

Abstract: The grounds of nine fifteenth-sixteenth century panels of the Castilian School were studied. The material used was gypsum in all cases. Examination as backscattered electron images by scanning electron microscopy showed the different morphologies of the materials used in the gesso grosso and gesso sottile layers. Energy dispersive X-ray analysis (SEM-EDX) was used to determine the purity of the gypsum and provide preliminary data on the nature of the associated minerals (dolomite, calcite and various silicates).

Original written sources for the history of mediaeval painting techniques and materials: a list of published texts

Abstract: Original written sources for the history of materials and techniques of mediaeval western art are very important for the scholar who wants to carry out research in this field. The author has selected and commented on those which he considers the most important among those that have been published: the ‘Lucca manuscript’, the De coloribus et artibus romanorum, the Mappae clavicula, the De clarea, the Schedula diversarum artium, the Breviloquium diversarum artium, the Livro de como se facen as cores, the Coloribus naturalia exscripta et collecta, the Liber de coloribus illuminatorum sive pictorum, the De coloribus faciendis, the De coloris diversis modis tractatur, the De diversis coloribus, the Experimenta de coloribus, Jehan Le Begue's recipes, Jehan Le Begue's Tabula de vocabulis sinonimis, Il libro dell'arte, the Segretti per colori, the ‘Strasburg manuscript’, the ‘De arte illuminandi’, the ‘Gottingen Model Book’ and the Ricepte daffare piu colori. The editions of the original texts containing ...

Absorbent grounds and the matt aesthetic in Post-Impressionist painting

Abstract: There is a well established tradition of matt painting in modem art; this paper concentrates on the period after Impressionism, paying particular attention to the role of absorbent grounds. They were adopted by Seurat, the Neo-Impressionists and van Gogh largely for plein-air painting. Toulouse-Lautrec, Gauguin, Bernard, Serusier, the Nabis group and Redon, on the other hand, employed them as part of a ‘matt aesthetic’ often linked to decoration. Drawing on sample analyses, supply catalogues and manuals, letters and art criticism, the paper surveys the different types of absorbent grounds used and their role in the production and appearance of the paintings.

Antwerp artists and the practice of painting on copper

Abstract: Artistic activity in Antwerp around 1600 is explored in the context of the city's role in the international copper trade and print publishing. The physical characteristics of copper plates used by Antwerp artists such as Brueghel and his contemporaries are discussed, as well as the painting techniques employed.

A note on the use of tin amalgams in marquetry

Abstract: Metal fillets removed from a Boulle clock were found to be badly corroded. Analysis showed that the fillets were made of a tin amalgam, formula HgSn7, containing 20 ± 1wt% mercury. The fillets were covered with a thick, uneven layer of corrosion made of a mixture of tin (II) oxide (SnO, romarchite) and tin (IV) oxide (SnO2, cassiterite). The corrosion of tin amalgams is discussed and documentary references to the use of tin amalgams to imitate silver inlay in cabinet making are reported.

Mars colours: preparation methods and chemical composition

Abstract: In the latter part of the eighteenth century, processes to manufacture various shades of iron oxide pigments using aqueous precipitation were developed. By the early part of the nineteenth century, treatises on artists' materials contained descriptions of how these pigments, generally referred to as 'mars colours', were produced. A study of documentary sources, combined with physical and chemical characterization of samples of historic mars colours, can yield information about the methods of preparation for the mars colours and the extent to which recipes in the treatises were followed. The process for making mars colours was based on the formation of an iron precipitate from an aqueous solution of iron salts and alkali. Once the initial precipitate had formed, it was oxidized in air to produce iron oxide hydroxide. While iron sulphate is the salt most often mentioned as a reagent, iron chloride, nitrate or acetate could also be used [1]. A number of different sources of alkali are mentioned in nineteenth-century treatises, including sodium carbonate, potassium carbonate and calcium hydroxide [1-3]. A late nineteenth-century notebook belonging to Jacques Blockx, who, in 1865, founded the pigment company that bears his name, gives detailed instructions for the preparation of mars colours [3]. From his records, it is clear that the process required a great deal of care and that the recipes had to be followed closely to produce the desired results. Six days were required to make a 5kg batch of raw pigment: one day for the initial mixing of the solutions and decantation; three days for washing; and two days for pressing and drying. A thorough washing was considered very important in order to remove all traces of acids and soluble salts from the pigment. Precipitations using only iron salts and alkali gave a yellowbrown pigment after oxidation [1]. However, variations on the recipes allowed the production of a wide range of colours. Alum (potassium aluminium sulphate) could be added to the iron sulphate solution, yielding a light-coloured yellow pigment. Orange and red pigments were prepared by calcining the raw yellow product [1, 3]. A number of methods to manufacture mars violet pigments are described: in an 1896 catalogue from the French pigment company G. Sennelier, mars violet is listed as 'oxyde de fer, cobalt', suggesting a mixture of iron and cobalt oxides [4]; a 1912 catalogue, also from Sennelier, indicates that mars violet was produced either by high-temperature calcination of iron oxide or by the addition of a manganese salt during manufacture [5]; and several nineteenth-century manuals state that the violet colour was created simply by repeated calcination of red iron oxide [6, 7]. For mars brown, Blockx indicates that vine black was added to mars yellow during the washing process [3]. In Riffault's nineteenth-century manual, however, the instructions state that salts of zinc, manganese, cobalt or nickel could be used as starting materials along with iron salts in order to produce specific shades of mars brown [2]. Mars colours that were examined for comparison to the recipes given in the documentary sources included nineteenth-century and early twentieth-century pigments from Winsor & Newton, Roberson, and J. Blockx fils, among others. The pigments were analysed using X-ray diffraction, Fourier transform infrared spectroscopy, polarized light microscopy, scanning electron microscopy and X-ray microanalysis. The results of the analysis of the pigments allowed some interesting observations to be made. For example, a mars brown pigment from Roberson, dated 1887 was found to be composed primarily of amorphous iron and chromium compounds, probably hydrated oxides of these metals. Although chromium is not among the metals listed by Riffault for use in mars brown pigments [2], its presence does indicate that recipes for mars colours employing metals other than iron were in use in the nineteenth century. Also of interest is the fact that the nineteenth-century mars violet pigments examined were found to be coloured by haematite alone. No cobalt or manganese compounds, mentioned in the catalogues from'Sennelier as components of mars violet [4, 5], were identified. The violet colour was produced simply by employing haematite with a larger particle size than that used for mars red pigments. Haematite particles of 0.1 to O.2Jlm appear bright red, while particles from 1 to 5Jlm appear blue-red to purple [8]. Red haematite can be converted to purple haematite by calcination, which causes sintering and a corresponding increase in particle size [8]. The use ofhaematite with a relatively large particle size in the violet pigments is consistent with the nineteenth-century manuals stating that mars violet is produced by calcination of red iron oxide [6, 7]. Extenders and white pigments, including gypsum, barium sulphate and aluminium oxide, were identified in some of the mars colours. Pigments which would brighten or modify the colour of the iron oxide were also present. An early twentieth-century sample of mars violet from Roberson, for example, contained an organic violet pigment Helio Bordeaux, Pigment Red 54 in addition to the iron oxide. Similarly, early twentieth-century mars red and yellow-orange pigments from Blockx et fils were found to contain chrome orange as well as haematite and goethite. While this work is preliminary in nature, it shows that careful scientific examination of historic mars colours combined with study of the documentary sources can shed new light on the preparation methods for these pigments. Kate Helwig is a conservation scientist at the Canadian Conservation Institute, Department of Canadian Heritage, 1030 Innes Road, Ottawa, Canada K1A OM5.

The recipe collection of Johannes Alcherius and the painting materials used in manuscript illumination in France and Northern Italy, c. 1380-1420

Abstract: A close reading of the recipe collection of Johannes Alcherius reveals the concerns of manuscript illuminators during the era of what is now known as the ‘International Style’. Collected during extended residences in Paris as well as in northern Italy, the recipes can be grouped according to four areas of interest: organic colourants, metallic effects, copper corrosion product green pigments, and the preparation of ultramarine blue. The recipes in Alcherius's collection are compared with contemporaneous manuscript illuminations. Preliminary non-destructive pigment analysis (using X-ray fluorescence and UV-visible spectrophotometry) on illuminated manuscripts from the collection of the J. Paul Getty Museum appears to confirm the direct relationship between technical treatise and the book illuminator's palette.

The relationship between Albrecht Dürer's palette and fifteenth/sixteenth-century pharmacy price lists: the use of azurite and ultramarine

Abstract: The pigments used in 13 paintings by Albrecht Durer have been identified: azurite, ultramarine, verdigris, lead-tin yellow, brown and, occasionally, yellow ochres, cinnabar, red lead, red lakes, basic lead white as well as plant and bone black. Durer mentions only four of these in his diaries and letters, and, except for ultramarine, there are no indications of where he obtained his pigments. Mediaeval documentary sources indicate that artists' pigments were available from pharmacies. Examination of fifteenth/sixteenth-century pharmacy price lists shows that all the pigments Durer used were available. The composition of the palette depended to a certain degree on the cost of the pigments. This is exemplified by the blues, and we focus on Durer's use of azurite and ultramarine. The nomenclature, origin, production and trade in azurite in late mediaeval times are discussed in more detail.