The painting is thought to be one of the Nolan's first experiments with abstract imagery of Ned Kelly's helmet. Art Gallery of NSW conservator Paula Dredge and Kendrah Morgan, a curator at Melbourne's Heide Museum of Modern Art, thought the brushstrokes suggested there was another figure lurking underneath, and they were right. With the help of scientists at the Australian Synchrotron and a fluorescent X-ray beam, they were able to reveal pigments buried underneath layers of paint, displaying the face behind the mask of Nolan's 1945 painting Ned Kelly, Nobody knows anything about my case but myself. The original painting and a virtual reality re-creation of the images underneath, prepared by Dredge and Andrew Yip from the University of NSW's Laboratory for Innovation in Galleries, Libraries, Archives and Museums (iGLAM), will be on show at Heide for the next three weeks. The image unearthed using the synchrotron is covered in coloured dots, which provide a clue as to who the painting might actually depict – Nolan, not Kelly.

The synchrotron was used to unveil the portrait underneath the finished painting. Credit:UNSW Nolan painted another self portrait, now held by Art Gallery of NSW, in 1943 – while he was in the army – in which he wears blue, yellow and red strips on his forehead, suggestive of an artist's war paint. This was during a period he spent in the army during World War II after being conscripted. Stationed largely around Victoria's Wimmera region, it was during this time that he developed the vibrant landscapes (25 of which are on display at NGV Australia) that featured in his landmark Kelly series. Two years later he absconded; he was granted a dishonourable discharge in 1949. Morgan believes the painting at Heide may have been among Nolan's first experiments with abstract imagery of Kelly, who loomed large in his family's folklore and to whom Nolan related while AWOL.

After painting the face that appears underneath, he turned the work – painted on cardboard – upside down and added the mask. "That's our understanding, that this is one of the first ever that Nolan painted the black square mask of Kelly," says Morgan. That theory came from the late Warwick Reeder, the former Heide director who acquired the painting for the museum. Morgan said she had heard a theory that the idea first emerged from Nolan peering through the mail slot in the door of the Parkville loft where he hid out in 1944-45 after fleeing the military. Nolan's grandfather William Nolan was a trooper recruited by Superintendent Francis Hare, who led the hunt for Kelly and his gang, in 1879 to help pursue "outlaws", Victoria Police records show. The painter had implied in several interviews that the Kelly series was more about himself than the outlaw, who was hanged in 1880.

"The paintings are really more about myself and my emotional state, than Kelly," Nolan told writer Janet Hawley during the 1980s. Rarely seen photos of Sidney Nolan and friends feature in the Heide exhibition. Credit:UNSW Art historian, curator and author Nancy Underhill, whose book Sidney Nolan: A Life was published in 2015, says she believes many of Nolan's paintings were self portraits, or had other imagery beneath the final painting. "I think a lot of them are portraits that are self portraits," says Underhill. "There are a lot of his pictures that have pictures under them. Certainly there are missing Glenrowan pictures that have been painted over." The discovery comes amid a major celebration of his centenary in England, featuring a series of exhibitions and musical events around the country, where Nolan spent the latter half of his life, under the auspices of the Sidney Nolan Trust, formed by the artist before his death in 1992, and discussion about how the milestone should be marked in Australia.

Yet in Australia there is no concerted effort to celebrate Nolan and his legacy. An exhibition was held by Sotheby's in Sydney several weeks ago. Heide, where Nolan lived and worked with Sunday and John Reed – a tryst that attracted almost as much attention as his art – has a year-long exhibition marking the centenary.



The National Gallery of Australia has 25 Kelly paintings, donated by Sunday Reed in 1977, at the centrepiece of a permanent display of the works. The Art Gallery of NSW will celebrate the centenary of Nolan's birth with an an extended display from the 136 of his works in its collection, along with a series of talks and workshops running through to August. Curator of Australian art, Denise Mimmocchi, says Nolan is one of the most significant Australian artists of the 20th century. "He changed the way we look at the landscape and think of the landscape," she says.



"He looked at the landscape in terms of the inner life of the place – he wasn't content with just the appearance of things. His Kelly series is a classic example of how he used myth and legend, and also history and place, to frame how we look at the landscape.



"It's hard to disassociate the way we think of Kelly country from that iconic black mask he painted."



Nolan's deep engagement with the landscape continued even after he moved to England in 1953, she says. "The places where he grew up and travelled to continued to inform his work. The terrains of Australia continued to inform his practice, even though he was a ceaseless traveller."



Nolan was "incredibly prolific and highly experimental", she says. "Part of the appeal of his work is that it's complex and perplexing. You don't always fully grasp what he's trying to get at."



The centenary of his birth is an opportunity to explore those complexities, she adds.



The important milestone has not been overlooked in the country of his birth, she says. "His importance is widely accepted and understood in Australia. He is a constant presence in our galleries in Australia.That is not so much the case in England." Jinx Nolan, the painter's adopted daughter, says she is disappointed more isn't being done in Australia to mark his centenary. "Can I use the word dereliction," she told Fairfax Media.