The use of scientific analysis in frames conservation can be illustrated by a case study of the frame formerly housing Sir Joshua Reynolds' The Age of Innocence (?1788, Tate N00307). 1 This painting was acquired by Robert Vernoni in 1844 and the frame is believed to date from then. In 1847, Vernon gave the painting, together with many others forming the Vernon Collection, to the nation.
The frame is a gilded reverse-section (bolection) frame in the Italian baroque style (Mitchell and Roberts 1996, p.29) constructed of moulded composition on wood (Fig.1). Regrettably some of the composition decoration had been lost and the gilding was very dirty and deficient in places (Fig.2).The frame was mostly oil-gildedii but the back cavetto, inner cavetto and the glazing frame2 (Fig.1) had been water-gilded.ii However on comparing a similar but larger frame from the Vernon collection of the same date, it was thought possible that the inner cavetto and the back edge had been altered when the glazing frame had been made (Fig.1).
Before starting conservation, small samples of gilding and substrate had been taken from the back edge, back cavetto, ogee cushion,4 torus, inner cavetto and glazing frame for microscopic analysis at x 250 magnification, using both reflected white and ultraviolet light to show the various layers.
Figs 3 and 4 show the layers in the samples from the back cavetto. The top surface shows water-gilding on a layer of bole and whitening.iii There is then gilding on a layer of oil-size that has been applied on a deep layer of a different whitening.
Rabbit-skin glue-size and oil-size can be seen to fluoresce when viewed with ultraviolet light (Fig.4). Acid fuchsine stains protein, such as rabbit-skin glue-size, pink (Fig.5).
The various samples were analysed using energy dispersive X-ray analysis.iv The qualitative and quantitative elemental composition of the same sample from the back cavetto (Figs 3-5), is shown in Figs 6-8.
Using the observations from all the samples, it is possible to deduce that because of its very fine particles of orange/red bole, the glazing frame is probably of late nineteenth or early twentieth century manufacture.5 The lower fragmentary dark-red layer appears to be synthetic iron oxides from the same period. The whitening is based on calcium carbonate with a small amount of sulphur probably from the glue size. The red bole is china clay with extenders and coloured with iron oxide.
The main frame whitening also has a calcium carbonate base for the whiting and the surface is oil-gilded. The back cavetto shows two distinct gilding schemes. The basal layer is of fine and transparent calcium carbonate with layers of glue-size, oil-size and gold leaf. Above this scheme is a thick layer of calcium carbonate-based whitening with traces of china clay and sulphur.6 The next layer is orange/red bole that is similar to that from the glazing frame, on top of which is water gilding.
The back edge has a basal layer of fine-grained whitening similar to the deep layer of the back cavetto. A layer of Mars yellow pigment paint and a thin layer of brown paint covers the deeper layer of whitening. More superficially, analysis revealed layers of whitening (with china clay), iron oxide and magnesium silicate, thick Mars yellow paint, thin brown paint and on top thin yellow paint.
The consistent use of calcium carbonate as the base for the whitening reinforces the probability that the frame is of English origin despite its Italian style (on the premise that it would be more common to find calcium sulphate with an Italian frame). The glazing frame, with its water gilding on red bole, is not original to the main frame, which is oil gilded on yellow bole. The back cavetto was originally oil gilded but later received more layers of whitening, red bole and water gilding. The back edge, although repaired, has retained its original basal layers and hence its shape had not been altered.
The scientific analysis of the decorative elements of the frame indicated that the inner cavetto was re-gilded at the same time as the frame was modified to take the glazing frame at the end of the nineteenth or beginning of the twentieth centuries. It also showed that the shape of the back edge had not been modified. It was appropriate, therefore, to re-gild the existing substrate, where damaged, using an oil-gilding technique and to leave the back edge unmodified. The analysis has therefore allowed a better understanding of the frame's earlier repairs and allowed informed decisions to be made about its most recent conservation.
February 2007
The work on which this paper is based was performed in the Frames Conservation Section at Tate during a work placement arranged by London Metropolitan University.
i. Robert Vernon (1774-1849) gave 157 pictures and 8 sculptures to the nation in 1847. This highly significant donation formed the basis of the National Collection of the British School of Art. This collection of then modern British art was given to the National Gallery but when the Tate Gallery was built as the home for the national collection of British Art in 1897, it was appropriate that the Vernon Collection should be displayed there. Over the years, virtually all the still-existing paintings from the Vernon Collection have been transferred there.
ii. Gold leaf when used as surface decoration may be applied on a layer of oil varnish (oil-gilding) or on a film of water. It is usually desirable that the gold leaf is laid on a very smooth surface. This is obtained by applying many of layers of whiting (usually powdered calcium carbonate or chalk in Britain but calcium sulphate or gypsum are also used, particularly in Italy) suspended in rabbit-skin glue-size to form whitening, or gesso when gypsum is used. The surface is abraded smooth when dry. A coloured bole (china clay containing coloured pigments) is often applied to the whitening. Traditionally a red bole (china clay containing a red pigment such as red ochre) in rabbit-skin glue-size is used for water gilding and a yellow bole (china clay containing a yellow pigment such chrome yellow) in rabbit-skin glue-size is used under oil gilding.
When water is applied to the bole, surface tension stretches the gold leaf and the size sticks the gold leaf to the surface. With oil gilding, a fine layer of oil-varnish based size is applied and when almost dry, the gold leaf is applied to the surface.
iii. Whitening is whiting (ground chalk) mixed with rabbit-skin glue-size to make a hard white substrate that can be abraded to a very fine smooth surface.
iv. The principle of energy dispersive X-ray analysis is that when molecules of a sample are bombarded with low-energy X-rays in the vacuum of a scanning electron-microscope, an X-ray detector is used to determine the different energies of the X-rays emitted from the sample. (The energy is proportional to wavelength of the ionising radiation.) The energies of the X-rays are unique for each element so the composition of a substance can be determined. The technique works particularly well for heavy metals but is less satisfactory for alkali and earth metals, which are lighter.
1. View this work in the Tate Collection
Sir Joshua Reynolds completed The Age of Innocence about 1788. Provenance: Reynolds sale, Greenwood's 16 April 1796 bought in; 1797 exchanged along with another picture by Lady Inchiquin (Reynolds' niece) for the 'Dido' to Bryan; sold by Bryan to Jeremiah Harman for 50 guineas; Jeremiah Harman sale, Christie's 18 May 1844, by Robert Vernon for 1450 guineas; presented by Vernon to the National Gallery in 1847 (Mannings 2000, p.507).
2. The glazing frame would have been a later modification in keeping with the National Gallery's policy of protecting paintings from both environmental pollution and the public (Anderson 2001, p.61). The policy started in the 1850s and continued until the 1930s. The frames now at Tate continued to be modified by the National Gallery's workshops until the 1930s.
3. Sancho Panza in the Apartment of the Duchess (1843-4) by Charles Leslie (1794-1859), acquired by Vernon in 1844.
4. Or Cyma reversa.
5. Whereas the main body of the frame dates from 1844.
6. Probably from the glue size.
