National Gallery Technical Bulletin Volume 15, 1994

Giovanni Battista Tiepolo's ‘Saints Maximus and Oswald’: Conservation and Examination

Larry Keith

Giovanni Battista Tiepolo's ‘Saints Maximus and Oswald’ (NG 1192) (Plate 1) was acquired by the National Gallery in 1885 and was cleaned and restored in 1934. By the summer of 1991 this restoration had significantly discoloured and, more important, the picture was evidently in need of structural treatment (which had not been undertaken since acquisition). The decision to restore the picture was based largely on its need for physical conservation, yet during this restoration several technical features became apparent that are of art-historical interest and are discussed in the second part of this article.

Conservation treatment

Some time before its acquisition the picture had been relined and mounted on a fixed-corner stretcher that was slightly too small for it and therefore could not be keyed-out to correct the painting's considerable forward bulge. The open-weave lining fabric, attached with some type of glue-paste mixture, had delaminated from the original canvas in several areas and provided little support. The paint and ground layers had developed a prominent raised craquelure, some of which was poorly attached to the canvas, with four small flake losses present in Saint Oswald's right shoulder. On the picture surface the varnish had yellowed and blanched, and showed poor saturation in dark areas such as Saint Oswald's body armour. Numerous darkened retouchings were visible in the sky, the most disturbing of which appeared as a series of roughly parallel vertical lines.

After local consolidation of loose paint with sturgeon glue in Saint Oswald's shoulder and elsewhere the picture was cleaned using conventional solvent mixtures of acetone and white spirit. Discoloured varnish and earlier retouchings were for the most part readily soluble. The paint surface was in excellent condition generally with the exception of some localised abrasion in the near spandrel relief figures and an old damage in the sky half-way up the left side of the far arch. The other old retouchings in the sky did not cover damages but were an attempt to hide visible underdrawing (see below); in fact their subsequent darkening exaggerated features they were intended to suppress.

The picture was next faced with Eltolene tissue and wax-dammar 'facing mixture' and then taken off its stretcher. The old lining fabric and adhesive were easily removable, and the original tacking edges were flattened. In addition to revealing an inscription, the removal of the old lining showed that the picture had been previously on a narrower stretcher, the marks from which were clearly visible outside those left by the more recent one (Fig. 1). The marks of the narrower stretcher bars also correspond to raised cracks in the paint film itself, suggesting that these represented the original stretcher configuration.

It was decided to attempt a reduction of the raised craquelure, leaving aside any subsequent decisions on relining, by means of moisture treatment on the Willard low-pressure table (note 1). A thin sheet of blotting paper that had been moistened by misting with water was laid on the pre-heated (35°C) table surface, onto which the picture was placed, face-up. The table was then covered with Melinex and a vacuum of 15 mbar was applied. After about 15 minutes the pressure was increased to between 20 and 25 mbar, while the dehumidification system of the table was used to reduce gradually the painting's moisture content to ambient conditions. The table surface heaters were switched off during drying. The most prominent raised cracks were also treated locally with a heated spatula from the front while the picture was under light vacuum.

This procedure reduced the raised craquelure to the point where it was no longer disturbing, although it was by no means eliminated. The treatment also appeared to have regenerated size layers and/or remnants of the earlier lining adhesive to the point where, combined with the earlier local consolidation, no further consolidation was judged necessary. It was decided that, given the controlled environmental conditions in the Gallery, the canvas was robust enough not to need relining and could be loose-lined instead.

A new stretcher that could be keyed-out was constructed, over which a Beva 371-impregnated canvas was tightly stretched. This loose-lining fabric would provide physical support and protection and act as a buffer against rapid fluctuations in relative humidity, all the more important given the now unlined state of the original canvas. After reinforcing the turnover edges with Beva-impregnated thin polyester net, the painting was hand-stretched over the loose-lining fabric. Retouchings were carried out using Paraloid B72 resin in xylene and dry-powdered pigments over Ketone-N resin varnish. Tiepolo's use of natural ultramarine in the sky(note 2) was matched in retouching with artificial ultramarine to avoid metameric colour shift.

Technical examination

The National Gallery painting is one of several very similar versions by Tiepolo, the two closest of which are in the Accademia Carrara in Bergamo and a private collection in New York (note 3). All three seem derived from a full-sized altar of the same subject (note 4) in the church of San Massimo in Padua, where the figure of Saint Maximus is virtually identical but the composition is otherwise significantly different. Another oil sketch in the Ruzicka Collection in Zurich is generally agreed to be the actual preparatory study for the altarpiece, and shows only minor variations from the final composition (note 5). While it is not possible to establish a firm priority of execution between the various versions from the investigation of one picture in isolation, closer examination of NG 1192 reveals several features that seem relevant to the eventual further clarification of their relationships to one another.

NG 1192 was painted on a double ground, with the lower layer a warm orange-brown of natural ochres with some black, and the upper layer a very light slightly warm grey predominantly of lead white with small amounts of black and ochre (Plate 2). This upper ground has basically been left in reserve to give the colour of much of the clouds as well as of the stone steps at the bottom. This double ground is unusual for Tiepolo's small format paintings, which are more generally built up directly over a warm orange-brown preparation similar in colour to the lower layer of the ground in the present painting (note 6). The lighter upper preparation gives a rather high-key, cool tonality to the picture as a whole (note 7); furthermore it is light and reflective enough to provide an unusually clear image with infra-red examination.

While a great deal of the underdrawing is easily visible to the naked eye, the composite infra-red reflectogram provides a more comprehensive view of the initial drawing-in of the composition (Fig. 2) (note 8). There is enough variation in the shape of the drawing strokes to suggest that Tiepolo used a typically mixed technique of brush and some sort of charcoal, as is common in his drawings (note 9). The roughly indicated contours of the clouds appear freely sketched with charcoal, whereas now partially covered elements like the lances in the background or the censer in the foreground seem to have been executed with a brush (Fig. 3). Some lines, such as those delineating the right vertical border of the picture, were probably ruled, but there is no indication of any mechanical transfer of a previously drawn composition onto the canvas itself. A small paint sample from this border shows the line to have been drawn with some sort of vegetable black pigment (note 10), although this does not necessarily indicate its use in the rest of the underdrawing.

The changes in the composition of the National Gallery version of the painting are numerous, both as departures from the drawing-in stage and as pentimenti within the course of painting. In addition to the censer and lances, a halo was sketched in around Saint Oswald's head and a keystone or armorial crest was drawn in the centre of the near arch, both of which were also left unpainted and partially covered. The near foreground has a drawn tessellated floor, establishing perspectival orthogonals which provide a convincing space on which the censer rested. Two other changes were made later in the execution of the painting: the alteration of the curve of the rear arch, and the modification of Saint Oswald's baton from its original form, a long and much higher halberd (note 11) in front of the near arch, which must have given a stronger forward projection to the principal figure group.

With the exception of the central keystone which appears in the New York picture (note 12), none of the abandoned compositional ideas of NG 1192 appears in the other versions. Furthermore, elements like the censer, the tessellated floor (note 13) and Saint Oswald's halo are all present in both the finished Padua altarpiece and the Zurich preparatory sketch, increasing the closeness of the London picture's derivation from them. The lances and halberd do not appear in the altarpiece, its sketch or the other derived versions. It is tempting to suggest that NG 1192 may have been the first derivation of the altarpiece, incorporating many of its compositional elements in its initial stages and even adding new features, but this would need confirmation through close technical investigation of the other versions to see if they show a similar compositional evolution. In any event the ensuing simplification of the National Gallery picture and other versions makes sense for the smaller format, where more of the image is taken in at a single glance and there is a greater need for compositional clarity. Even in the absence of conclusive information about the relationship of the National Gallery picture to the other versions it does seem clear that in Tiepolo's studio the derivation and production of multiple versions was a more fluid process than might have been imagined.

Acknowledgement

I would like to thank Rachel Billinge, Leverhulme Research Fellow, for her production of the infra-red reflectogram.

Notes and references

1. For a fuller description of this type of treatment and an extensive bibliography see Paul Ackroyd, Anthony Reeve and Ann Stephenson-Wright, 'The Multipurpose Low Pressure Conservation Table', ‘National Gallery Technical Bulletin’, 12, 1988, pp. 4–16.
2. Determined from paint cross-sections and confirmed by the lack of absorbtion of infra-red rays in the course of reflectography.
3. See Michael Levey, ‘The 17th and 18th century Italian Schools’, National Gallery Catalogues, 2nd edn., London 1986, pp. 214–18. All are illustrated in A. Morassi, ‘A Complete Catalogue of the Paintings of G. B. Tiepolo’, London 1962, figs. 137–42. (NB Morassi's figure numbers are reversed for the illustrations of the New York and London pictures. )
4. There is in fact some scholarly debate about the identification of the subject of the National Gallery picture and its variants, although there is at least general agreement about the compositional derivation from the Saint Massimo altarpiece. See Levey, op. cit., pp. 214–15, and note 19, p. 217.
5. Levey, op. cit., p. 214. The Ruzicka sketch and Saint Massimo altarpiece are illustrated in Morassi, op. cit., figs. 140–1.
6. This is well illustrated in Tiepolo's depiction of an unfinished painting within both versions of his ‘Alexander and Campaspe in the Studio of Apelles’, now in Montreal and Paris. See Morassi, op. cit., pp. 29–30 and 38, fig. 284 and colour plate II.
7. This difference is apparent in comparison with the National Gallery's ‘Saints Augustine, Louis of France, John the Baptist and a Bishop Saint’ (NG 1193), which has a similar compositional format but the more usual darker, warmer ground.
8. For a full description of the National Gallery's infra-red reflectography equipment and procedures, see Rachel Billinge, John Cupitt, Nicolaos Dessipris and David Saunders, 'A Note on an Improved Procedure for the Rapid Assembly of Infrared Reflectogram Mosaics', ‘Studies in Conservation’, 38 no. 2, 1993, pp. 92–8.
9. Numerous illustrated examples of this mixed technique, most commonly pen and wash over black chalk (sometimes with additional white highlighting), can be found in Jacob Bean and William Griswold, ‘18th Century Italian Drawings in the Metropolitan Museum of Art’, New York 1990, pp. 192–247.
10. Identified from cross-section. The black particles did not show the characteristic shape of charcoal samples.
11. Visible in the reflectogram and on close inspection with the naked eye. In the X-radiograph the visibility of the halberd is obscured by the stretcher bar. On the iconographic significance of particular attributes see Levey, op. cit., pp. 214–15 and note 19, p. 217.
12. Morassi, op. cit., fig. 138 (mislabelled as fig. 139).
13. The Zurich and Padua pictures employ an off-centre perspective, while the National Gallery perspectival orthogonals recede to a more central point in keeping with its symmetrical architecture.

Series Editor: Ashok Roy

© National Gallery Publications Limited 1994
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First published in Great Britain in 1994 by National Gallery Publications Limited 5/6 Pall Mall East, London SW1Y 5BA.

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Edited by Diana Davies and Jan Green

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