Two years ago, a man in Ireland decided it would be a good idea to put his fist right through a £10 million Monet painting, completely destroying the left corner of the photo. That man's now serving 5 years in jail, but thankfully the team at the National Gallery of Ireland were able to completely repair the painting, entitled Argenteuil Basin with a Single Sailboat, which dates back to 1874. This is how they did it:
Before the painting was moved from the exhibition space, conservators examined it for signs of loose paint and flaking, securing any loose fragments temporarily. Any fragments found on the floor were carefully collected and stored. The painting was then laid flat and stabilised on the front and back.
The conservators then needed to find out exactly what sort of paint Monet used - oil, glue or resin-based. They did this by examining pieces of the painting at a microscopic level. Solvent-testing and ultraviolet imaging suggested that the varnish was a modern synthetic resin with some added wax. Tests also indicating indicated that the bright red and yellow paints were very sensitive to solvents.
A conservation grade tissue was then adhered to the varnished surface of the painting for protection, allowing work to be done with the aid of a high-powered microscope and appropriately small tools. The tear edges were carefully aligned thread-by-thread, re-joining the broken canvas fibres by applying a specially formulated adhesive to achieve a strong but reversible bond between the thread ends.
Over 100 of the tiny fragments from the floor, measuring between 0.3mm and 1mm, were then delicately reinserted into the painting. Unfortunately. some of these pieces had simply been smashed to dust by the man's punch, so these areas had to be filled with gesso - a material made from chalk with a small percentage of animal gelatine glue. This was pigmented to match the original priming layer of the painting and was carefully painted using watercolour.
So there you have it! Many man hours later and at the cost of a "five figure sum", the painting is now back in its rightful place.