The Picasso that's been in the wars

He painted Guernica to expose General Franco's tyranny, and refused to let it return home until the dictator was dead. Now it's showing the scars of its global tour, say Alasdair Fotheringham and Enjoli Liston

Guernica was commissioned by the Republican government, after the Basque city was bombed in the civil war (Getty Images)

Every night, after the last visitor to Madrid's Reina Sofia Museum has left, the prestigious art gallery's newest curator flickers into life. The expert is a ground-breaking robot, which this week began the most exhaustive research exercise ever performed on Picasso's controversial masterpiece Guernica. Its mission: to establish the true extent of the damage that the painting has suffered in its turbulent 75-year lifetime.

Running on a network of rails across the 3.5- by 7.8-metre work, the robot will use the latest infrared and ultraviolet scanning technology to take millions of high-definition images of areas as small as 25 microns (25 thousandths of a millimetre). These will build up a 3D virtual image of the painting, which restorers will use to assess its condition.

Guernica was commissioned by the Spanish Republican government, which wanted Picasso to create a work to represent the nation at the International Exhibition in Paris, in 1937. The result was a black-and-white depiction of tormented figures reflecting the horrors of the civil war that gripped Spain at that time. The painting's title is the name of the ancestral capital of northern Spain's Basque region, which was bombed that same year by aircraft from fascist Italy and Nazi Germany – allies of Spain's future dictator, General Francisco Franco. Historians estimate that the attack killed up to 1,600 people, and Picasso's representation has become one of the most studied paintings in the history of modern art.

After the exhibition, the painting went on a 20-year tour of museums across the world. The rolling and unrolling of the canvas for transportation took its toll, and by the 1960s Picasso reportedly declared: "Enough is enough." But it was not until 1981 that Guernica made its final journey home from the Museum of Modern Art in New York, to which Picasso had loaned it until democracy had been restored in Spain.

Telefonica, a Spanish telecoms company sponsoring the new project at the Reina Sofia, said in a statement that it is the first "full-scale health check" on the painting since 1998, when it was judged to be in a "very precarious condition". That analysis found 129 imperfections in Guernica, including cracks, creases, marks and stains, which were attributed to its chaotic history. As a result, the work was banned from being moved again.

In 2008, the Reina Sofia (where the painting finally settled) X-rayed Guernica again to check it had not deteriorated further. The results showed that although the imperfections had not increased, the painting had been damaged during restoration after a graffiti attack in 1974. Some critics said it was in a "dangerous" state of repair, while others argued it was fit to move again. However, experts say this new study will be more comprehensive than any that have gone before, and will finally determine the true state of Guernica.

"This is a real breakthrough," Professor Teresa Espejo, an expert in restoration at the University of Granada, told The Independent. X-rays allow restorers to see "the inside of the painting" and examine the state of the canvas, but ultraviolet imaging will also show any repainted sections and mistakes, and infrared will even display underlying sketches, Ms Espejo says.

"We've been using some of these techniques, like ultraviolet photos, for more than 20 years... but what is so innovative is they will all be digitalised in the same computer," she said. "Such precise combined photos revealing, say, the exact nature of the different types of paints used will be amazing."

Once the robot's work on Guernica is complete it will be used on other key works of art in the Reina Sofia. Guernica itself will be the centrepiece of a new exhibition on 1930s art, due to open at the gallery in autumn.

However, if restorers decide the painting could be fit for another move, it could lose its status as a permanent exhibit at the Reina Sofia. Miguel Zugaza, director of the Prado Museum, claims that Guernica's rightful home is there – as Picasso stated in his will. The Guggenheim Museum in Bilbao (20 miles from the town of Guernica) has also staked its claim to the artwork.

But Manual Borja-Villel, director of the Reina Sofia, told the Spanish daily ABC on Tuesday: "Taking [Guernica] out of the museum would be taking it out of its context and the case is closed." He also denied calling Spain's Minister of Culture to ensure the painting stayed put. "It's not new for one gallery to want works of art from others. I could fancy having the State Hermitage collection [in Moscow], but it doesn't cross my mind to call [Russian President Vladimir] Putin," he said.

In the picture: The story of Guernica

Picasso is commissioned by the Spanish Republican government to create a work to mark the bombing of Guernica (a town in the Basque region) in 1937 by Italian and German forces at the behest of the Nationalists during the Spanish Civil War. The painting goes on display at the Paris Exposition later that year.

When the Exposition finishes, the painting is sent on a tour to publicise the violence of the fascists and to raise funds for the Republican cause. After exhibitions in various Scandinavian capitals, it is displayed in London's Whitechapel Art Gallery in 1939.

Guernica returns to France because Picasso refuses to allow the painting to travel to Spain after General Franco's Nationalists take control later that year. It is shipped to New York soon after Poland falls to the Nazis later in 1939. It finds shelter in New York's Museum of Modern Art (MoMA).

The painting tours the US until 1952. It visits Brazil between 1953 and 1956, then travels to various European cities, returns to MoMA, and then goes to Chicago and Philadelphia. Concerns about the painting's deterioration see it returned to MoMA, where it undergoes its first restoration, in 1957.

Picasso dies in 1973. Vietnam War protester Tony Shafrazi spray-paints "KILL LIES ALL" across the painting a year later. He says he attacked it to bring it up to date. Curators at MoMA restore it, but damage it in the process.

In 1981, Guernica returns to Spain after Franco's death. MoMA lost its attempt to argue against the move by claiming that Spain had not become the republic that Picasso put in his will as a condition for the painting's repatriation.

Guernica moves from Madrid's Museo del Prado to the Museo Nacional Centro de Arte Reina Sofia in 1992. Basque nationalists have since argued that it should be housed in the Guggenheim in Bilbao, but it remains in Madrid.