A WORK believed to have been drawn by a Venetian artist and bought for £30,000 has now been attributed to one of the greatest artists in history by experts at the National Galleries of Scotland.

Detective work by one of the leading curators at the Scottish National Gallery in Edinburgh has led to the rare sketch now being credited to Titian. Experts say no value can now be put on the work.

The sketch, which shows three figures, was bought at a Sotheby's Old Masters sale in 2007, when it was attributed to another Venetian artist, Jacopo Bassano (1510- 1592).

Aidan Weston-Lewis, the gallery's chief curator, had already suspected the work, which had also been linked to Tintoretto in its long history, was not what it seemed and was, in fact, a compositional sketch by the great Italian painter of the 16th century.

Now the sketch has been formally attributed to Titian and hangs in a new exhibition of Titian And The Golden Age Of Venetian Art, which runs from today until September 13 at the Scottish National Gallery.

Mr Weston-Lewis would not speculate on what the sketch, in black and white chalk on blue paper and dated to around 1550, is now worth - especially as the galleries can never sell it - but Titian created few sketches, perhaps 30, and the work would now worth "significantly more".

"We have seen some astronomical sums at auctions recently and this would not be out of that league," he said.

In 2012, a sketch by Raphael was sold for £29.7million at auction in London, setting a record price for any drawing in art history.

The curator said the drawing shows all the style and detail of a Titian drawing, with the outline of three forms that had been repeatedly re-worked, including localised streaks of white chalk.

Another drawing by Titian, of the Agony In The Garden, in the Uffizi museum in Florence, Italy, is very close in form to the drawing, and Mr Weston-Lewis says that although it does not appear to be a study for any surviving Titian painting, it could be a study for a work in the Prado called La Gloria.

He said: "I had always very much believed the drawing was by Titian.

"Of course it is a matter of opinion because the drawing is not signed and there are no absolutes, but there is a confluence of arguments, and if you bring them all together it makes for a very convincing picture.

"You try to reach a consensus, and I haven't had it gainsaid, in fact my case has been favourably received (by other curators and experts)."

The new exhibition also features two Titian paintings saved for the nation by the National Galleries of Scotland and the National Gallery in London: Diana And Actaeon and Diana And Callisto, which were bought in 2009 and 2012 for a total of £95m.

The acquisition of the two Diana paintings guaranteed the continuation of the Bridgewater Loan to the galleries, a collection of key paintings owned by the Duke Of Sutherland, until at least 2030.

The two paintings are displayed together on a rotating basis between Edinburgh and London.

Also being shown for the first time in Scotland is Titian's late masterpiece, The Death Of Actaeon, from the National Gallery, London.

It is the first time it has been lent anywhere since the National Gallery acquired it in 1972.

The picture was intended as part of the same series as the two Diana scenes, but was not completed by the artist and remained in his studio until his death.

The exhibition includes 16 paintings and some 30 drawings and prints by most the leading names in Venetian art of the period.