From the museum website:
The goldfinch (1654) by Carel Fabritius (1622-1654) is one of the most famous 17th-century Dutch paintings. The Mauritshuis is restoring the panel for the Fabritius exhibition in 2004. Conservator Jørgen Wadum is removing the severely discoloured varnish in order to reveal the original colours.
Between 8 April and 2 May one of the galleries will serve as a restoration studio. This studio is open to all visitors.
Tuesday through Friday (except for 30 April)
From 1:00 pm to 2:45 pm: the conservator is at work.
From 2:45 pm to 3:00 pm: the conservator will answer any questions you may have.
Siemens Nederland NV has provided technical equipment for the restoration