In preparation for a recent exhibition on Monet's botanical paintings entitled Monet - The Garden Paintings, a Dutch conservator, at Gemeentemuseum in the Hague(Kunstmuseum Den Haag), discovered the presence of a variation of Monet's Water Lilies series beneath Monet's lesser-known painting Wisteria (1917-20). After painstakingly removing a layer of World War II era varnish, conservators discovered the presence of in-painted areas that concealed damage sustained to the painting by broken glass. Conservators x-rayed the painting and inadvertently discovered the Water Lilies variation beneath. This discovery supports the theory that there is a direct stylistic link between the famed Water Lilies series and the lesser-known later Wisteria works.
The paintings so called Bords de la Seine à Argenteuil (Banks of the Seine at Argenteuil)has been the subject of much authentication controversy. It was previously offered for sale at a reserve price of £500,000, which the sale ultimately failed to meet. It was then bought by its current owner for £40,000. The current owner has made numerous attempts to have the painting accepted by the Wildenstein Institute which publishes the catalogue Raisonné of Monet's works. The painting was submitted for a battery of technical and chemical tests on the show Fake or Fortune; the experts of which concluded the painting was genuine. The Wildenstein Institute has continued to reject the painting as a fake. The current owner brought the issue to the French court, but his request to force the painting into inclusion into Monet's catalogue Raisonné was ultimately denied by the Paris Court of Appeal in 2015.
The painting The Seine at Port Villez,that was initially accepted as a Monet after being donated to the Wallraf-Richartz Museum in 1954, was found to be a fake in 2008. A series of scientific tests were done in preparation for an exhibition. The exhibition would include details of the artist's process. The results of those tests led museum experts to conclude that the painting was not painted by Monet. The museum retains the painting, but with clarified provenance, and maintains five other authentic Monet paintings in their collection.
Finland's Gösta Serlachius Fine Arts Foundation acquired A Haystack in the Evening Sun(1892) in the 1950s but were unable to securely authenticate the work as an autographed Monet. The signature, that was discovered by mathematical information technology department researchers at Finland's University of Jyväskylä, had been long obscured by a layer of paint. Other scientific tests followed, securing the attribution to Monet.
Claude Monet's Waterloo Bridge, London from 1903 was discovered among Hildebrand Gurlitt's secret collection of art, some of which were purchased legitimately. But some of the Gurlitt collection was looted from Nazi-occupied nations during World War II. Gurlitt's son Cornelius, who was charged with maintaining the secrecy of the collection, eventually attracted the attention of authorities after attempting to bring a large amount of money into Switzerland. He eventually agreed to assist investigators in the task of locating the rightful owners of his collection. This long-lost masterpiece was discovered in the suitcase that Cornelius had brought with him to the hospital where he eventually died.