THE American artist John Singer Sargent, who along with his novelist friend Henry James adopted England as a second home, is being honoured this week with a major retrospective of his work at the Tate Gallery.

The exhibition, co-curated by his great-nephew Richard Ormond, who is director of the National Maritime Museum in London, includes exceptional loans from private and public collections in its 150 works.

They include Madame Ramn Subercaseaux, a portrait kept in Chile after a Paris showing in 1881 and never previously seen in Britain. It has been cleaned specially for the occasion.

Another portrait originally shown in Paris is Madame X, on loan from the Metropolitan Museum of Art, New York.

The Imperial War Museum in London has loaned the monumental Gassed, which Sargent painted after seeing soldiers blinded by mustard gas in the First World War.

Mr Ormond, who has co-authored the comprehensive catalogue of the artist's work, said he was delighted to see at first hand the portrait of Mme Ramn, "the Chilean lady", loaned by a private collector descended from the sitter. "This is rather special for us," he said. "It's one of those lost, mystery pictures that hasn't been seen, sitting in Santiago."

The artist met Ramn Subercaseaux, Chile's consul in Paris, at the 1880 Salon; his wife, Amalia, admired Sargent's painting Fumee d'ambre gris, and Ramn asked him to paint her. "At that stage Sargent was still regarded as pretty avant-garde. He was only 24 or 25," Mr Ormond said.

Sargent, later famous for insisting that sitters come to his studio, went to the couple's apartment in the Avenue du Bois du Boulogne to paint the 20-year-old Amalia.

Mr Ormond said: "We have seen black-and-white pictures of this painting, but seeing it in the flesh, and seeing it cleaned ... we are thrilled that we made the effort to bring it over ... among the Sargent cognoscenti it's one of the key works."

The exhibition opens on Thursday and runs to 17 January. It will later go to Washington and Boston, and is not only the first exhibition to show Sargeant's full range of work, including water-colours and drawings for murals, but also the first large-scale exhibition of his works to be seen in both Britain and the US.

Sargent, who was born of American parents in Florence in 1856 and counted Claude Monet among his friends, was commemorated with a retrospective at the Royal Academy shortly after his death in England in 1925. He has enjoyed something of a resurgence in esteem in recent years, and is particularly popular with American collectors. His Carnation, Lily, Lily, Rose is, a Tate spokeswoman said, one of the public's favourite paintings.

Stories abound about the artist's idiosyncrasies. Osbert Sitwell, for example, recalled in his memoir how his family's considerable entourage was uprooted from Renishaw, near Sheffield, to Sargent's London studio for a portrait. He wrote: "There were enacted from time to time considerable scenes, though, even then, the sudden outbursts of the artist, his rushing bull-like at the canvas and shouting, were in reality the expression more of tremendous physical vitality than of rage."