AUSTRALIAN art expert Geoffrey Smith told Victoria's Supreme Court yesterday that his former partner sold a group of Sidney Nolan works on paper despite Mr Smith's reservations about their authenticity.

Mr Smith is executive chairman of Sotheby's Australia and a former curator of Australian art at the National Gallery of Victoria who is suing Robert Gould, owner of Gould Galleries in South Yarra, for a share of the estimated $32million to $50million in assets they amassed in their 14-year relationship.

"I just said that I wasn't 100per cent comfortable with those works of art. I wasn't saying they weren't by Sidney Nolan categorically but I just had some concerns about the material, about the technique, about the paper that they were on," Mr Smith told the court.

When his counsel Richard Kendall, QC, asked what happened to the Nolan works, Mr Smith said Mr Gould had sold them at his Sydney gallery.

Mr Smith told the court that during their relationship he advised and introduced clients to Mr Gould.

Asked by Justice John Dixon if collectors sought Mr Smith's advice because he was associated with Gould Galleries or with the NGV, Mr Smith replied: "People knew that I was an authority on Australian art, full stop."

Mr Smith, who was in a full-time position at the NGV during their relationship, said he would talk to Mr Gould up to 10 times a day by telephone on Gould Galleries business.

Mr Gould's counsel, Simon Wilson, QC, opened his cross-examination of Smith by asking if he had undertaken public speaking training at the NGV.

"Can you tell me why it is during the whole of this case so far you've hardly removed your eyes from His Honour when you've been sitting in the witness box?" he asked. "You think that's something that's important, do you, to make eye contact with the judge and try and persuade him that you are an honest witness ...?"

Mr Smith replied without taking his eyes off Justice Dixon: "This is what I'm comfortable with. I believe it's respectful."