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Kunsthaus Zürich

Puttying and retouching

After the removal of the non-original layers, a number of areas which had suffered paint loss became apparent. These are located mostly in the outer areas near the panel edges, though some are found in the centre of the panels as well. The removal from the wall in the late 50s was the obvious cause for a lot of the damage. The upper row of panels displays an almost continuous area marked by broken edges and paint loss.

In addition, the removal of the added layers exposed some major discoloration (see overview image.) On the one hand they can be recognized as darkened areas covering the entire surface, on the other they make for a grid-shaped, brownish pattern. Various scientific analyses allow the conclusion to be drawn that the yellowed binder of the added non-original layers is the origin of these two phenomena.

Overview of Panel 8 after the removal of the added layers.
Overview of Panel 8 after the removal of the added layers.

Before it was possible to reintegrate areas with paint loss into their backgrounds in terms of colour, they had to be puttied and the surface texture had to be adapted. The putty used for the mural is glue and chalk based. It was applied with a palette knife and was then levelled and smoothed out. Subsequently, the surface was textured using a paintbrush.

As the areas with paint loss were to be retouched using water soluble colours, the putties were covered with a thin layer of acrylic paint. This will prevent the putties from being solubilised in case the retouches will have to be removed.

Damaged areas and areas with missing paint and varnish after the removal of the added layers
Damaged areas and areas with missing paint and varnish after the removal of the added layers

At first the retouches are applied in gouache instead of oil paint (as were used in the original) because they remain water-soluble. Reversibility of the processes is thereby maintained.
However, because the degree of sheen cannot be fully matched with gouache, the initial retouches are glazed with a coat of resin. In this way they are enhanced in terms of depth of luminosity and sheen whilst also receiving a thin protective coat. This coat of resin is so thin, that it could still be removed with humidity should it take on a stain.

Damaged areas after fill-ins with chalk-based putty
Damaged areas after fill-ins with chalk-based putty
Damaged areas after initial retouching. The final glazing has not yet been applied.
Damaged areas after initial retouching. The final glazing has not yet been applied.

Concerning the darkened areas and the grid-shaped, brownish pattern, a different approach was chosen: on the blue background the discolorations were reduced with a thin bluish layer using aquarelle coloured pencils. With this slightly transparent layer the colour value could be altered whilst obtaining the surface’s lively character. However, this method could not be employed for the yellow areas as the coloured pencils’ opacity was not sufficient to cover the grid-shaped, brownish pattern. Instead, they were covered with gouache first and then complemented with coloured pencils.