Why was the painting treated?
The Pietà, attributed to Gerard David (c.1455-1523) and workshop, has a thin oak panel support with the wood grain running in a vertical direction. The fine-scale craquelure of the paint film mostly follows the direction of the grain. When the painting was examined, it was found that the craquelure was not stable and that the paint was pushing up with sharp and lifting edges and there was some paint loss. This may have been caused by the oak panel suffering from constriction and compression in a frame, at an earlier time.
In order to prevent further paint loss it was necessary to ‘consolidate’ the area, by delivering adhesive between and beneath the cracks. However, the varnish was so thick that this was not possible. The only way to secure the unstable paint film effectively was to remove the old varnish layers and overpaints first.
Removing the discoloured varnish and old overpaints
Combinations of solvents were used to solubilise and remove the discoloured layers of varnish, using small swabs of cotton wool. This image shows the partly removed varnish over the sky area. It illustrates how the relatively bright blues were obscured by the discoloured varnish.
Once varnish removal was completed, there were still a number of much older retouchings from previous campaigns of restoration, notably along the lower edge, covering old damages.
These may have been caused by flood damage at some point in the history of the painting. It was necessary to remove these older, less soluble retouchings as well, in order to secure the unstable paint film. Solvent gels were used to safely remove the areas of overpaint and old putties without risking damage to the original paint film.
As the varnish and retouchings were removed, so it became possible to feed the adhesive successfully into the paint film and stabilise the lifting edges of the cracks. It was necessary to consolidate the whole paint surface.
Re-varnishing and retouching
Once cleaning and consolidation were complete, the original surface of the paint film was brushed with an isolating coat of varnish, before the old losses were filled with fresh putty and retouching commenced.
The puttied losses were retouched using dry pigments bound in egg. Egg tempera allows the conservator to build up thin layers of paint to mimic the artist’s technique. In this case, the artist used relatively strongly coloured lower layers that were tempered by subsequent semi-transparent glaze layers to subtly adjust the tones.
Any areas of old damage on the rest of the painting were retouched using dry pigments bound in resin. Finally the painting was sprayed with a further protective coat of varnish.
Examining the painting with infrared reflectography
Whilst the painting was in the studio, it was a good opportunity to examine it using infrared reflectography. This allows us to ‘see through’ the painting to the initial freehand drawing.
The infrared reflectogram of the Pietà reveals skilful underdrawing in a liquid medium. The underdrawing carefully maps out the two figures and the skull with close hatching for areas of deep shadow, for instance in the drapery:
There are several pentiments in the underdrawing where the artist changed his mind. For example, the same area of drapery shows that some of the hatched lines were subsequently painted over with landscape and a tree. Other pentiments include the right side of his face, the white cloth at the Virgin’s right elbow, and as illustrated, Christ’s right hand, which was lengthened considerably during the painting process:
The drawing of the loincloth is also clearly visible with the naked eye since the thinly painted area allows us to see through to the ground layer quite easily.
The artist was probably making a copy of another version of the painting as it was a popular image. The skill of the underdrawing could indicate the hand of the master, or that of a talented member of his workshop.