Sir Peter Blake is one of several artists supporting the campaign
Titian's masterpiece Diana and Actaeon has been unveiled at the National Gallery in London, as a campaign to keep the painting in the UK continues.
The painting is on loan from the Bridgewater Collection, which hangs in the National Gallery of Scotland.
The public will have just four weeks to see Titian's great masterpiece in London before it returns to Edinburgh.
The two galleries are hoping to raise £50m to jointly buy the painting before a deadline of 31 December.
If they raise the funds to buy Diana and Actaeon, then a second painting - Diana and Callisto - will be offered for sale in four years.
The Duke of Sutherland is offering the works to the galleries for £50m each - one third of their estimated open market value.
They were created as part of a cycle of works for King Philip II of Spain between 1556 and 1559.
John Leighton, director general of the National Galleries of Scotland, said the two paintings that campaigners were trying to save were "amongst the greatest works of art anywhere in the world".
"We have had a very good response from the public. Even a £5 or £10 donation is important. The more people who get involved and support this, the easier it is to make the case for funding."
Diana and Actaeon was painted in the 16th century
He added: "We hope that the display of the Titian in London will encourage even more people to back our campaign."
The Art Fund - the UK's leading independent art charity - announced last week it would donate £1m to the campaign, the largest grant for a single work in its 105 year history.
More than 60 artists from all over the UK have also joined the campaign to save the Titians, including Lucian Freud and Sir Peter Blake.
Dr Nicholas Penny, director of the National Gallery, said he was hopeful of raising the money needed before the December deadline.
But he admitted the financial crisis was affecting the campaign, saying it was a "difficult time".
"The painting's display in London is an extraordinary opportunity to see one of the greatest of all European paintings in an entirely different context.
"It is also part of our joint campaign to secure not only this painting and its pair for the British public, but help assure the future of all the masterpieces in the Bridgewater Loan for the National Gallery of Scotland for decades to come."