A disputed painting found hanging in Sir Francis Drake's former home, Buckland Abbey in Devon, has been declared an original Rembrandt self-portrait, worth £30 million.
The 17th century painting of the Dutch master was dismissed for decades as a lacklustre work by one of his disciples. However, experts have used the latest scientific tests to prove the 379-year-old picture is by Rembrandt himself.
Dated 1635 and signed by Rembrandt, the painting has now been cleaned and restored.
It had been shrouded in mystery since art historian Horst Gerson first claimed it was bogus in 1968. Members of the Rembrandt Research Project came to the same conclusion and when it was donated to the National Trust in 2010 it was put in storage for 18 months.
But it is now considered one of the trust's most important artworks after a Rembrandt expert changed his mind and declared it was an original. Ernst van de Wetering revised his opinion after decades of study revealed "fluctuations" in the artist's style. He decided the crude brushstokes he had previously dismissed resembled other Rembrandt pictures of the same period.
National Trust chiefs decided to send the painting to the Hamilton Kerr Institute in Cambridgeshire to settle the question once and for all.
Paintings conservator Christine Slottvedd Kimbriel used techniques including infra-red reflectography, X-rays, raking light photography and pigment and medium analysis.
She said: "Careful cleaning and removal of several layers of aged and yellowed varnish, which had been added to the painting much later, revealed the original colours and painting style beneath. What was revealed was a true depth of colour, much more detail and a three-dimensional appearance to the fabric in Rembrandt's cloak which had previously been obscured and detracted from the quality of the work in the eyes of the Rembrandt Research Project.
"Next, it was close investigation of the artist's signature that gave us one of the biggest clues as to its true authenticity. The signature and date of 1635, inscribed both on the front and back of the panel, had been considered problematic in previous assessments as it was thought that the style and composition was much more akin to the artist's style slightly later in his career.
"But the cross-section analysis left no reason to doubt that the inscription was added at the time of execution of the painting."
Experts also carried out carbon-dating on the wooden panel on which the picture was painted.
The National Trust does not sell its items, and the painting has since been returned to go on display at the former Cistercian abbey, which was founded in 1278. Drake bought the building in 1581 and lived there for 15 years, as did many of his descendants until 1946, when it was sold to local landowner Arthur Rodd. He presented the property to the National Trust in 1948.
David Taylor, paintings and sculptor curator at the trust, said: "With the technical analysis backing up Ernst's claims, we are obviously very excited."