From the KIK-IRPA press release, 20 June 2014
Since June 2013, the conservators of the Royal Institute for Cultural Heritage (KIK-IRPA, Brussels) have continued work on the paintings on the exterior side of the wing panels. After removing the yellowed varnish they gradually realised that a considerable part of the visible paint layer is in fact overpaint. Due to the extent of the repainting, its good condition and the fact that the age crack pattern follows that of the original paint layer in most places, this intervention had never been detected or even suspected. The overpaint affects the garments of most of the figures (the donors, the Archangel, the Virgin and the Sibyls), the architectural backgrounds (niches, walls, columns) and the sculptures of St John the Evangelist and St John Baptist. Overpaint also includes highlights on the faces and hands of the figures.
The observations of the restorers were confirmed by analysis of tiny paint samples by the laboratories of the KIK-IRPA, research with the 3D Hirox microscope of Ghent University and MA-XRF research by the University of Antwerp. These analyses were combined with cleaning tests on the paintings to determine whether the overpaint could be removed without causing damage and to evaluate the condition of the original paint layer beneath. Fortunately, the latter is in reasonable condition, with relatively little abrasion or paint loss, and the exceptional quality of the Van Eyck brothers work is revealed. In the light of these findings, the international expert committee recommended the continuation of the process of removal of the overpaint. This treatment is proceeding centimetre by centimetre and is carried out with a scalpel under a binocular microscope. Patience, precision and experience are the keys to success in this endeavour.
The discoveries have both aesthetic and iconographic implications. Most of the overpaint follows the original forms, but the early painter-restorers did not succeed in imitating the Van Eycks’ dextrous handling of the paint and unrivalled depiction of light and materials. Lost under the overpaint is the exceptional sense of three-dimensionality and the subtle play of light and shadow. For example, cast shadows and a corner with cobwebs were found hidden behind the plain black overpaint in the Elisabeth Borluut panel, leading to a new iconographical reading of the donor portraits.