A painting of Tainui chief Kewene Te Haho, bought by Waikato charity for $121,000, has been judged a fake.
The supposedly 120-year-old work, bought at auction by the philanthropic Trust Waikato in 2001, hung in Waikato Museum of Art and History in Hamilton unquestioned until Wanganui artist Peter Ireland saw it in January and got suspicious.
"It just did not look like a Lindauer to me. There was absolutely no sign of ageing."
Trust chief executive Bev Gatenby had Victoria University School of Art History, Classics and Religious Studies lecturer Roger Blakeley take an initial look and asked Sarah Hillary, of Auckland Art Gallery, to conduct forensic tests.
While the tests proved inconclusive, Hillary, who compared the Waikato painting with another Lindauer at her gallery, concluded the painting was inconsistent with the artist's technique.
After receiving her report this week, Blakeley was convinced the painting was a "good fake".
"Sarah Hillary's findings strongly support the conclusion that your painting is a calculated forgery of a highly sophisticated nature, which for over a decade has successfully duped a range of experts," Blakeley said.
Dr Gatenby said she had gone back to International Art Centre, which had sold the painting in 2001, and it stood by the sale.
The trust had reported the matter to the police and was now seeking legal advice. Its next move would be decided by the board.
In February it was revalued, for insurance purposes, at $175,000.
International Art Centre director Richard Thomson said: "Saying it is a fake is a very strong statement, and I'm not about to comment on that. The people you need to talk to are the people who've been hanging it for 10 years - this is really not my business. We could ask a lot of questions about a lot of paintings."
Toby Braun, a litigation partner at Harkness Henry in Hamilton, said the trust could ask a court to find whether the painting was a fake and if it did take action against the gallery for breach of contract. Criminal proceedings could also be a possibility.
Dr Gatenby, who became chief executive six years ago, said she was disappointed by the findings.
A Waikato Times report of the investigation on Saturday had prompted the victims of a 1987 burglary to come forward and ask whether the painting was theirs. An identical painting, sold as a Lindauer copy in 1960, had been stolen from their home and never recovered.
Trust Waikato chairwoman Ali Van der Heyden said the board would decide at its next meeting in December what to do with the painting. "Irrespective of who the artist is, the artwork remains a magnificent painting of a Tainui tribal chief and will always have significance to the people of Waikato."
Blakeley said: "The appropriate milieu for such a work is a museum where it might function as an enlightening document in relation to the history of forgery in New Zealand.
For this reason alone retention of this painting should be considered a desirable option."