National Gallery of Canada / Musée des beaux-arts

Bulletin 5 (III:1), 1965

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Conservation Treatment of a Painting
by the Transfer Method

by Mervyn Ruggles, 
National Conservation and Research Laboratory

Résumé en français

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In June 1963 during the course of periodic inspection of the National Gallery collection, the Franklin Brownell (1) painting, Autumn on the Gatineau, after closer examination, was round to have developed paint cleavage (Fig. I) in several areas and partial separation from the support fabric. Normal consolidation procedure for this type of symptom is to infuse adhesive through the interstices of the canvas to the ground preparation and to apply gentle pressure from the front. A new lining canvas (2) is usually added to reinforce the original support by means of a non-hygroscopic thermosetting adhesive. (3)

The Brownell landscape had already been lined in 1944 (Fig. 2) and now additional treatment was required. Under the binocular microscope examination of the paint cleavage located at upper edge to the right and near lower right corner (Fig. 3) revealed that separation was occurring between the commercially prepared ground layer and the fibres of the original support. In the light of this information, the decision was made to remove the auxiliary canvas so that further infusion of adhesive could be attempted.

The original support, identified as jute fibre woven with 12 warp and 12 weft threads per inch, was covered by the commercially applied ground 1.2 mm in thickness. This type of artists' canvas was in fairly common use in eastern Canada during the 1916 to 1920 period. Cotton canvas had been employed as the lining material. Actual paint thickness ranges between 1 mm to 2.5 mm.

The first step in the conservation procedure (4) consisted in temporarily protecting the whole paint surface by applying wet strength tissue facing paper with diluted parchment size and stretching the painting on a temporary framework by means of paper strips. (5) By doubling back the auxiliary cotton canvas and pulling carefully the liner could be peeled off easily. At this stage, the layer of water-soluble animal glue remaining over the jute was round to be filling the interstices of the jute but had not penetrated sufficiently to the ground layer. This disclosure confirmed what had already been suspected during the examination. Furthermore, the impossibility of bringing about efficient infusion of the proposed thermosetting adhesive through the jute was now apparent.

Tests in marginal locations indicated that the jute could be shaved off carefully without undue danger to the underlying strata. Steps were now taken to carry out the unusual procedure of complete removal of the original canvas and to 'transfer' the paint and ground layers to an entirely new support. This operation is to be avoided if at all possible and is undertaken only when other treatment is not feasible.

Figure 4 illustrates the method employed to remove the jute threads after the front of the picture has been firmly sealed to a 1/8 inch-thick cardboard (6) under vacuum on the hot table. (7,8) The cardboard in position (Fig. 5) provides a rigid support while the jute fibres are shaved off with a knife blade. The back of the landscape with the jute completely removed, revealing the ground layer, can be seen in Fig. 6.

The new flax canvas (9) having been prepared by impregnation with warm wax adhesive, and the back of the painting coated in like manner using the same adhesive, bonding of the two was carried out on the vacuum hot table. After this stage, the cardboard front was no longer necessary having served its purpose and was peeled away as demonstrated in Figs. 7a and 7b. Removal of the tissue paper facing was accomplished by using naptha-water emulsion (Fig. 8).

The specially designed hot table (Fig. 9) at the National Gallery consists of a 3/8 inch-thick aluminum plate 5 x 8 feet, heated by electrical elements (10) sealed to the underside. The peak temperature during operation was 76° Centigrade. A temperature controller prevents overheating. Uniform pressure over the whole surface of the painting is achieved by covering the canvases with a thin rubber latex sheet and withdrawing air by means of a vacuum pump connected to the table, thus allowing the atmosphere to press the two fabrics together until cooled to room temperature by means of a built-in fan. The curve in Fig. 10 illustrates the heating cycle as charted automatically while the vacuum hot table is functioning, in this instance for 135 minutes duration.

The appearance of Autumn on the Gatineau after the old yellowed damar varnish coating had been dissolved away with diluted diacetone is shown in Fig. 11, where white spots are gesso luting material used to compensate for old paint losses. These were inpainted with pigment in normal butyl methacrylate medium. Finally, two applications of normal butyl methacrylate resin dissolved in xylene were sprayed over the surface after a two week drying period.

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