The first step was to remove the varnish, which was a natural resin one and could therefore be taken off with a light dissolvent. The next step was to remove the overpainting. This consisted of two layers, of which the upper one had pigments that were only used from the 19th century onwards. While the layers of overpainting were easy to distinguish and were separated from the original paint by the isolating layer, the original paint was very fragile and dissolvents could not be used. For this reason and given the small size of the painting, it was decided to remove the paint manually using a scalpel and the help of a stereoscopic microscope. Using the highest possible magnification made it possible at all times for the restorer to identify pigment that was not part of the original work, which is painted in egg tempera.
After this overpainting was removed, Saint Agnes and the donor reappeared in remarkably good condition. The bright colours of their clothes suggested that the other figures of Christ and the Apostles might also have been retouched (which proved to be the case) as they had a thicker texture, darker and more opaque colour range than the original tempera seen on the donor and saint. With the assistance of the Museum’s Laboratory, which analysed micro-samples of the green of Saint John’s mantle, it was confirmed that these figures had two pictorial layers separated by a layer of varnish, in other words, the overpaint on the surface and the original paint underneath it. These areas of overpainting were also removed in the same way as those on the donor and saint, by hand with a scalpel and the assistance of a microscope.
Once cleaning was complete, the restorer proceeded to replace any losses to the paint surface, which were small in size and few in number given that this panel is in exceptionally good condition. This was done with watercolour and the help of a microscope in order not to cover any of the original paint. With the aim of preserving the panel’s lively colours it was decided to use a natural dammar varnish applied in a very thin layer. At the end of the restoration process it was evident that the painting had recovered its original quality, the liveliness of its bright colours and the relationship between the different pictorial planes as they recede into depth.
More information about restoring.