Hammer attack on Reynolds portrait of Dr Johnson

Curators at the National Portrait Gallery were last night assessing the damage to a painting by one of Britain's most influential 18th-century artists after it was attacked by a man wielding a hammer.

The £1.7m portrait of Samuel Johnson by Sir Joshua Reynolds was set upon shortly before closing time on Wednesday evening. A man smashed the protective glass and drove the hammer right into the canvas. The National Portrait Gallery said it believed the masterpiece could be restored but it was unable to estimate how much it would cost. "Until the painting has been professionally assessed by a qualified painting conservator it is not possible to give a reasonable assessment of the cost of repair," a spokesperson said. "The good news the painting is repairable and is already being looked at."

A man gave himself up without resistance to security staff, who held him until the police came. A spokesperson for the Metropolitan Police said last night they had charged Mark Paton, a 44-year-old homeless man with one charge of criminal damage and a separate charge of possessing a hammer with intent to cause criminal damage. Mr Paton is expected to appear at City of Westminster magistrates' court tomorrow.

The National Portrait Gallery said it was unable to comment specifically on the nature of the damage to the painting because those details were part of an ongoing police investigation but there were reports that the glass had been hit several times and that the hammer was left embedded in the canvas.

The gallery had only recently stopped compulsory bag checks which had been brought in as part of its response to the heightened security risk after he failed car bomb attacks in London in June. Bag checks have now been reintroduced and the gallery said it was happy with the level of security arrangements.

The last time a painting was attacked in the National Portrait Gallery was in 1981 when a portrait of Diana, Princess of Wales, by Brian Organ, was slashed by a member of the public wielding a knife. The painting was painstakingly restored and can still be seen at the gallery.

Throughout his life Reynolds painted a number of portraits of his friend Dr Johnson, usually depicting the essayist looking serious or deep in thought. The portrait damaged on Wednesday, which was composed shortly after Dr Johnson published his famous Dictionary of the English Language, is unusual in that it shows Reynolds' friend looking relaxed while sitting at a writing table.

The two giants of 18th-century culture met through Henry Thrale, a wealthy brewer who assembled regular meetings of London's intellectual elite at his house in Streatham Park. Although Dr Johnson was often indifferent to visual works of art, he was fond of Johnson's portraits which were regarded as some of the best of the time.

The National Portrait Gallery owns 36 portraits of Samuel Johnson, 26 or which are by Sir Joshua.

An artist inspired by Raphael

Joshua Reynolds was born in Plympton, Devonshire, on 16 July 1723. He studied with the portrait painter Thomas Hudson, but it was only when he returned from Italy, where he studied the works of Raphael and Michelangelo, and classical Roman art, that his career took off. Reynolds became the first president of the Royal Academy of Arts in 1768 and was knighted in 1769. He died on 23 February 1792, and is buried in St Paul's Cathedral.