Varnish removal testing
Safe varnish removal
Take a close look at The Night Watch and you’ll find several small rectangular areas that are matte. These are the sites of tests to determine whether it’s possible to remove varnish from the 1970s and 90s from the paint layer and, if it is possible, what method should be used.
Old varnish layers
Old masters were coated with a layer of transparent varnish to produce saturated colours and to protect the paint surface. The varnishes used at the time were usually made from a natural resin that yellows with age and becomes less transparent, somewhat obscuring our view of the image. This is why restoring paintings often involves removing and replacing varnish. The layers of varnish currently covering The Night Watch are not original: they were applied as part of restoration treatments in the 1970s and 90s. Conservators have carried out varnish removal tests to determine whether it is possible to remove the old varnish layers and to improve our understanding of the (solvent and mechanical) sensitivity of the paint layers. As a result of the tests you will find small rectangular areas that are matte on the painting.
First phase
Two methods of varnish removal have been tested. The first, traditional, method involves soaking a cotton swab in solvent and rolling it over the surface of the painting. The second method involves holding a special microfibre cloth containing solvent against the surface, dissolving the varnish which is then absorbed by the cloth. Both methods were tested at multiple sites on The Night Watch. They were then studied extensively using an OCT scanner, UV photography, and a stereo microscope. The provisional conclusion is that the microfibre cloth method produces the best results.
Second phase
It was discovered during the first phase that remnants of older varnish layers are present that are less soluble than the more recent layers. This residue was missed by previous restoration treatments, and tests are currently being carried out into ways of removing it using supplementary solvents and methods. The results of these tests will be taken into account when considering the options or proposal for treatment of The Night Watch.