The official signing ceremony was almost ambassadorial. Russian and British flags adorned the panelists' table. The key players - Pushkin museum director Irina Antonova, Tate Britain director Stephen Deuchar, and Russian businessman Alisher Usmanov - were lined up to sign the document.
Stephen Deuchar said how the exhibition represented a continuation of close UK-Russian cultural relations, "at the moment when the `From Russia' exhibition at the Royal Academy of Arts is just drawing to a close".
Joseph Turner, Romantic and precursor of Impressionism, had a great impact on art in Britain and the whole of Europe. He also had at least tenuous connections with Russia. "Turner knew Aivazovsky and thought highly of him, so there is an obvious link with Russian art," Irina Antonova said.
To highlight this connection, the Pushkin Museum plans to devote its traditional "December Evenings" festival to Romanticism and to invite British musicians to the festival's concerts.
As part of the deal, Tate Britain will send 40 paintings, 70 watercolours and two prints to Russia. Deuchar singled out two of the paintings for particular note - Turner's 1799 Self-Portrait, a painting that seldom leaves British shores, and 1845's Norham Castle, which was not shown to Turner's contemporaries for fear that his admirers would not appreciate experiments with colour which, Mr Deuchar says, bring Turner closer to later artists than his contemporaries.
"The Turner exhibition will be the most expensive in the history of our museum and it could not have been held without a the assistance of a generous patron," said Antonova.
Panelists at the press conference, however, refused to disclose the exact cost (though Irina Antonova seemed to come close to spilling the beans at one point during the conference, before checking herself and saying "you can't even imagine how much it will cost").
For Mr Usmanov, his main motivation was a "passion for the arts and for two of the world's greatest museums: the Tate and the Fine Arts Museum.
"And in any case," he added, "this is not the last of my money."
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