Not many people know that in 1972, more than three years before the infamous knife attack on 14 September 1975, there were already plans about a possible treatment of The Night Watch. The varnish, applied in 1947, had become so brittle that even dusting the painting had become difficult. The varnish had also become quite yellow over time.
Research in secret
A fragment of the varnish was analyzed by the Centraal Laboratorium voor Onderzoek van Voorwerpen van Kunst en Wetenschap, but to keep it a secret, it was done under the name of a different, less important painting.
Mastic varnish from 1947
From the analytical results it was concluded that the varnish was mastic, which was in accordance with the written sources from 1947. Interestingly, mastic varnish was at that time specifically chosen to avoid the use of solvents in future treatments. It could be removed mechanically by gently rubbing the varnish away; however, this was a treatment method that had become obsolete by the 1970s.
Attack and treatment proposal
A treatment proposal was discussed in 1973 and a plan was established to start varnish removal the year after. However, as sometimes happens, other priorities took over and the treatment was delayed, until, on 14 September 1975, postponement was no longer possible. The twelve knife slashes made the necessity of treatment immediate. It was perhaps a small comfort for the conservators and other staff members in the stressful days, weeks and months after the attack, that the idea of treatment had been around for some time already and had made them better prepared than they would otherwise have been.