Brian Singer

The identification of synthetic organic pigments in modern paints and modern paintings using pyrolysis-gas chromatography–mass spectrometry

AbstractA collection of more than 70 synthetic organic pigments were analysed using pyrolysis-gas chromatography–mass spectrometry (Py-GC–MS). We report on the analysis of diketo-pyrrolo-pyrrole, isoindolinone and perylene pigments which are classes not previously reported as being analysed by this technique. We also report on a number of azo pigments (2-naphthol, naphthol AS, arylide, diarylide, benzimidazolone and disazo condensation pigments) and phthalocyanine pigments, the Py-GC–MS analysis of which has not been previously reported. The members of each class were found to fragment in a consistent way and the pyrolysis products are reported. The technique was successfully applied to the analysis of paints used by the artist Francis Bacon (1909–1992), to simultaneously identify synthetic organic pigments and synthetic binding media in two samples of paint taken from Bacon’s studio and micro-samples taken from three of his paintings and one painting attributed to him. FigureDulux orange paint in the studio of Francis Bacon, now located at Dublin City Gallery, The Hugh Lane

ANALYSIS OF WHITE AND BLUE PIGMENTS FROM WATERCOLOURS BY RAMAN MICROSCOPY

Summary The application of Raman microanalysis to the investigation of pigments taken from watercolours is described. The pigment samples identified include calcium carbonate (chalk), titanium dioxide in its anatase crystal form, zinc oxide, barium sulphate and ultramarine taken from a selection of watercolours. The Raman spectra of the white pigments and extenders barium carbonate, lead carbonate, lead sulphate and calcium sulphate (gypsum), and the blue pigments cerulean blue, Prussian blue, indigo, copper phthalocyanin and lapis lazuli, are also reported.

An investigation into the use of a laser for the removal of modern ink marks from paper

Abstract The use of a Q‐switched Nd:YAG laser for paper conservation is investigated and discussed. The laser is used to remove a variety of common writing inks from cotton and woodpulp paper; the effectiveness of ink removal and the level of damage acquired by the paper surface at differing laser pulse energies are assessed. The laser beam parameters of spot size, waist, and profile are determined, and used to control the laser beam incident on the paper surface. Photomicroscopy and scanning electron microscopy (SEM) are used to further investigate the damage caused to a cotton rag paper as a result of laser removal of ball point pen ink. A Nd:YAG laser can be used for safe removal of ballpoint inks from cotton papers. The laser is characterised so that the pulse fluence is known and controllable. A fluence of 29 ± 1 Jcm‐2 per pulse was found to give optimal ink removal on Roma 100% cotton paper.

Aquazol as a consolidant for matte paint on Vietnamese paintings

This article describes the consolidation of two Vietnamese portrait paintings that had suffered flaking paint, tenting and blind cleavage. Scientific analysis revealed the presence of zinc sulfates as a result of the degradation processes. This posed consolidation issues since zinc sulfates are very water soluble. A discussion of paint characteristics demonstrates the particular requirements of consolidants. The effect of consolidants and their manner of application on matte paint films is elucidated, followed by a description of testing of consolidants. The only consolidant suitable for use was found to be Aquazol, hence this was tested at length before being used to consolidate the paint layers. Aquazol was also used as a filling and retouching medium. The properties of Aquazol are discussed, and two potential methods of identification of Aquazol, when used as a conservation material, were demonstrated; using Fourier transform infra-red spectroscopy (FTIR) and pyrolysis gas chromatography mass spectrometry (Py-GCMS).

Examination of a blooming problem in a collection of unvarnished oil paintings

Abstract The bloom found on three late nineteenth century unvarnished paintings by W H Chariton, all on commercially prepared grounds was investigated. The grounds, paint media and bloom were analysed using gas chromotography ‐ mass spectrometry and differential scanning calorimetry. Raman microscopy, energy‐dispersive x‐ray analysis and other techniques were used to identify the pigments. It was found that the bloom on these paintings consisted of a mixture of free palmitic and stearic acids. The effect of pigments used in the paintings and in the underlying compositions on the density of the surface bloom was investigated. The presence of an impervious material, Melinex was a possible contributory factor in the formation of the bloom.

Investigation of the materials found in the studio of Francis Bacon (1909–1992)

Abstract The investigation of materials found in Bacons studio is reported. The contents of the studio are examined and interpreted to identify the materials and colours most favoured by Bacon, and the range of media used. A small number of colours appear to have been heavily used. Some objects used as tools in the painting process are also investigated and explain textures seen in paint in his works. Samples of selected materials from the studio are analysed to identify the components of paints (pigments, extenders, and binders) used by Bacon. This investigation is part of a wider project examining his materials and techniques. The analytical information obtained here from the studio helps to clarify the statements made by Bacon in interviews regarding his use of materials and is proving useful in the identification of materials in his paintings, in order to help with the conservation and authentication of his works.

The materials and techniques used in the paintings of Francis Bacon (1909-1992)

Abstract Materials from 38 paintings by Francis Bacon (1909–1992), including 21 complete works and 17 partially destroyed canvases are investigated. Observations are made of the artists technique and details are compiled of the supports used. Samples of paint and priming were taken for analysis using polarized light microscopy, Fourier transform infrared spectroscopy (FTIR), gas chromatography–mass spectrometry (GC–MS), pyrolysis–GC–MS (Py–GC–MS), and scanning electron microscopy coupled with energy dispersive X-ray analysis (SEM–EDX). Analysis of priming layers appears to show that the priming composition correlates well with particular ranges of dates. A fairly limited range of materials are found, with many of the same pigments found in works spanning Bacons career, though other pigments were introduced at different stages in his career. Oil paints were used consistently for the painting of figures, but household paints were increasingly used in backgrounds from the 1960s onwards. A variety of different synthetic media are found in later works, including household acrylic paints and spray paints. Increased knowledge of Bacon’s materials is expected to be of great value to conservators caring for the work of this highly significant artist, and is already helping in the authentication of works attributed to him.

A study of unusual degradation on a seascape painting associated with the use of zinc white pigment

Summary The authors investigated the reasons for the poor condition of S.S. Buda, painted in 1889 by G. Thomson, a gouache/watercolour on medium-weight cotton/linen rag paper. The paper was generally severely discoloured and it was concluded that this was due to a combination of photodegradation and sulphur dioxide pollution. The work of art included some passages painted in zinc white and there were some particularly unusual effects associated with this pigment. These included an efflorescence, which was shown to be zinc sulphate, causing blistering effects and the raising of the paper into a ridge. A further effect was a paler colour in the paper beneath and around the zinc oxide giving a paler ‘halo’ on the front of the image. This was in contrast to the darkening effect on paper which zinc oxide usually promotes. This latter effect was thought to be due to zinc oxide acting as a base and protecting the paper from the acids associated with sulphur dioxide pollution.

The Treatment of Oil Paintings on Paper Supports Considerations on the Treatment Applications Used from the Past until the Present

From the past until the present, oil paintings on paper supports have usually been treated in the same way as oil paintings on canvas, mainly by painting conservators. During the last few decades, with the development of the specializations in the conservation profession, the treatment of this type of work became a grey area between paper and painting conservators. However, a combination of paper and painting conservation disciplines is regarded as essential for their treatment, since the layers overlaying the paper support correspond to those of oil painting on canvas, present similar problems and require analogous interventions. The fact that oil paintings are biaxially heterogeneous laminar structures results in a dynamic interaction between the painting layers and the support, having as a consequence optical, chemical, and mechanical alterations caused by the conservation treatments applied. Thus, any conservation approach raises a lot of issues. All these motivated a series of interviews with artists, and painting and paper conservators working in the public and private sector, as well as in educational institutions in Athens (Greece), that gave the ground for exchanging views and experiences with professionals abroad. The structure of the oil works on paper supports in Greece, the common problems of this type of works, the treatments and materials used, the effect of the applications in time, and the recommended interventions according to the present knowledge were the main themes of discussion. The outcome of these was complimented with a literature review on the matter. However, the applicability of the methodologies and materials used both in paper and painting conservation for the treatment of this type of works are debatable. The change of attitude towards the aesthetic and structural integrity of these works is regarded essential. Historic materials and interventions still used for the treatment of oil paintings on paper were recorded and evaluated to provide a basis for the development of a recommended conservation approach for this type of work in the future.

Investigation of a ‘white cast’ on a mid‐nineteenth‐century watercolour painting

Abstract The appearance of a ‘white cast’ on the blue areas on a nineteenth‐century watercolour is described. Investigation using energy dispersive x‐ray analysis and x‐ray diffraction showed that the white cast consisted mainly of an efflorescence containing calcium sulphate dihydrate and that some excess alumina found in these areas may have also contributed to the whitish appearance. The possibility that the calcium sulphate may have been derived from yellow lake pigments is discussed. The alternative idea that the efflorescence has been derived from the interaction of sulphur dioxide with calcium carbonate, which is present both in the mixture of pigments in the paint layer and also as a filler in the paper, is discussed.