Schlüsselwörter
(Englisch)
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Cuno Amiet; tempera; reconstructions; accelerated ageing; binding medium; Gas Chromatography Mass Spectrometry
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Forschungsprogramme
(Englisch)
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COST-Action D42 - Chemical Interactions between Cultural Artefacts and the Indoor Environment (EnviArt)
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Kurzbeschreibung
(Englisch)
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Our initial study of early paintings by the Swiss painter Cuno Amiet (1868-1961) has brought to light a series of degradation phenomena which seem to be associated with his choice of binding medium during his highly experimental period of 1902-1915. The study of written sources, including Amiet’s own correspondence, and of the technical treaties used by him, combined with the ongoing analytical characterisation of samples taken of a relevant selection of his early paintings, have begun to shed light on the complexity of these binding media. The combined use of drying oils, egg, resins and gums is both implied from the written sources and suggested by the first analytical data. The compilation of this information will allow the selection of materials and recipes for the preparation of suitable paint reconstructions. Exposing these to controlled diverse environmental conditions it is hoped to better understand the influence of temperature, relative humidity and light on the chemical and optical properties of paints with the composition found in a particular selection of Amiet’s paintings. The pilot project proposed here will bring together the analytical laboratories of the Schweizerisches Institut für Kunstwissenschaft (SIK) in Zürich and of the Studiengang Konservierung und Restaurierung at Hochschule der Künste (HKB) in Bern. The outcome of this pilot project will provide relevant basic information on the behaviour of complex oil tempera paints and prepare the ground for further studies towards the development of better preventive and treatment strategies.
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Weitere Hinweise und Angaben
(Englisch)
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Full name of research-institution/enterprise: Schweizerisches Institut für Kunstwissenschaft Leiterin Labor und Technologieforschung
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Partner und Internationale Organisationen
(Englisch)
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AT, BE, CH, CZ, DE, DK, EE, ES, FI, FR, GR, IE, IL, IT, MK, MT, NL, NO, PL, PT, RO, SE, SI, SK, TR, UK
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Abstract
(Englisch)
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A comprehensive art historical and technical study of the early painted oeuvre of the Swiss painter Cuno Amiet (1868-1961) is currently underway at the Swiss Institute for Art Research (SIK-ISEA). We know that Cuno Amiet was fascinated by the expressive possibilities offered by diverse paint systems and application techniques and experimented widely with them. From the study of a range of sources including his own correspondence, it is known that in his early years, Amiet used homemade emulsion paints of varied and complex composition, the information on which paint formulations were used and for which paintings, is less concrete and has to be determined analytically. This pilot project has two main objectives. First of all to improve the analytical strategy for the study of microsamples in order to allow characterisation of complex mixtures present in Amiet's early paints with minimal intervention and secondly to better understand their chemical alteration induced by environmental factors, in particular light. The evaluation of the mentioned written sources led to the identification of one specific paint recipe Amiet most likely has used and one specific painting he most used it for. The source of the recipe was a technical publication by A.W. Koenig of 1897 and the recipe that of an egg/oil-tempera consisting of 'egg yolk, some egg white, a little vinegar, linseed oil, some soap, and some water'. No further details of relative quantities were given, however through the reconstruction of this paint formulation it became clear that little variation of the quantities of the ingredients was permitted in order to paint with suitable working properties. A combination of analytical methodologies for the analysis of the reference materials and the completed binding medium mixture was developed. These were studied by Fourier transform infrared spectroscopy (FTIR), direct temperature-resolved mass spectrometry (DTMS) and gas chromatography mass spectrometry (GC-MS). FTIR proved very useful in the non destructive analysis of microsamples (5-10 ug) and the characterisation of the main classes of compounds present. DTMS could be carried out on the same microsamples and provided additional information of the paint film compositions including the presence of tri-, di-, and monoglycerides, free fatty acids, as well as inorganic pigment components. Of particular importance is the detection of sterols (such as cholesterol and its oxidation products) and proteins as these are markers for egg. This analysis was shown to be successful when associated with a micro solvent-extraction step separating lipids from the proteinaceous and pigment sample components. After comparing different sample preparation methodologies for GC-MS analysis of lipids and proteins it was established that using hydrolysis and silylation enables amino-acid and fatty-acid characterisation in a semi-quantitative manner, although this methodology requires samples sizes that can not always be safely collected from paintings. Nonetheless this method provides more accurate information on the type and condition of the lipid and proteinaceous materials present (i.e which oil and the confirmation of egg as the protein source.) However the analytical development stage has clearly shown that the minor components which play an important role in the working properties of the paint are difficult to detect. This is the case for example of vinegar which evaporates and is no longer detectable in the dried paint film and soap which is present in very small quantity and therefore has its signal masked by those of major compounds in the case of DTMS and FTIR analysis and in the case of GCMS, the derivatised products from Marseille soap are also amongst those of linseed oil. With this exception the combination of the three techniques proved successful. The painting Amiet created with the egg/oil-tempera paint medium is 'Self-portrait with spouse' (1899). The study of this painting on a short term loan from the Museo d'arte Lugano, presented itself as a unique opportunity to assess if the reconstructed paint system prepared at SIK-ISEA were chemically similar and if they could provide a paint surface with similar optical and physical properties to that of the double portrait. This optical and physical comparison shed further light into Cuno Amiet's paint preparation technique in particular concerning the procedure of mixing pigment and binding medium. It was apparent that although the microsamples collected from the painting were chemically distinct from the reconstructed paints although the main functional groups were common. The hypothesis that the chemical alterations are a result of interaction with the environmental factors was then tested. The adequate procedure for the preparation of strips of reconstructed paint recipe was developed and three pigments available to Cuno Amiet and used by him in the double portrait were selected, namely synthetic ultramarine, cadmium orange and lead white. The reconstructions were prepared and were subsequently exposed to light in an artificial light chamber for a total of 1650 hours at 50 W/sqm mimicking the spectrum of daylight through glass. ?Alteration of the physical and optical properties of the paint such as brittleness and colour became noticeable. Microsamples from the aged and control paint strips were analysed by the methododlogy developed. The chemical alterations associated with the light exposure such as oxidation, the formation of metal soaps, the hydrolysis of ester bonds, etc. can easily be followed by FTIR. DTMS provides additional information of the paint film alteration including the formation of diacids and oxidised sterols as as result of light exposure, the levels of hydrolysis and formation of metal soaps. Using this combination of techniques the light ageing process of the paint film can be followed. It was clearly to observe that light exposure causes severe photooxidation of the lipid unsaturations from the oil with the formation of diacids, the oxidation of sterols, namely cholesterol, the oxidation of the protein side groups, thus severely affecting the chemical profile of the samples. The comparison of the microsamples collected from the double portrait with that resulting from light ageing suggests that Amiet used egg tempera as binding media. Publication of the full details of the analytical results is in preparation. The outcome of this pilot project was successful and has provided new analytical tools and strategies for the identification of egg/oil tempera binding media in paintings after long term natural ageing. It is now clearer which markers remain detectable after light induced oxidation and which oxidation products can be expected from such complex binding media.
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Datenbankreferenzen
(Englisch)
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Swiss Database: COST-DB of the State Secretariat for Education and Research Hallwylstrasse 4 CH-3003 Berne, Switzerland Tel. +41 31 322 74 82 Swiss Project-Number: C07.0131
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