Drawing is one of 22 works made in 2002 as therapeutic activity about his incarceration

This article is more than 1 year old

This article is more than 1 year old

Of all the sketches he made about his 27-year incarceration, this was the one Nelson Mandela wanted to keep. A depiction of his Robben Island cell door with a key in it – a powerful symbol of hope and resilience.

Now the previously unseen drawing – one of 22 sketches Mandela made in 2002 as therapeutic activity – is to be sold, according to the auction house Bonhams.

While 10 of Mandela’s drawings were reproduced as lithographs to raise money for the Mandela Foundation, The Cell Door, Robben Island was a particularly special work for the anti-apartheid activist.

“For him, painting was a way of relaxing, but also making sense of the past,” said Mandela’s daughter Makaziwe, who is selling the work.

“This work held a particular significance for him as it was a constant reminder that he could not forget what seemed unforgettable and that he should not take freedom for granted.”

Mandela spent 18 years of his long incarceration on Robben Island. Cell number 5, the subject of the work, has become a place of pilgrimage whose visitors have included Bill Clinton and Barack Obama. It was tiny. Mandela wrote in Long Walk to Freedom: “I could walk from one side to the other in three steps.”

Giles Peppiatt, Bonhams’ director of modern and contemporary African art, said he knew the family had drawings and had been working to persuade them to put one in a sale.

“This is one of the most poignant and important of the ones they’ve got, because it is such a wonderful image, it meant so much.”

Peppiatt said the key in the lock was a symbol that showed hope where there might have been none. “The work demonstrates his indomitable spirit with characteristic honesty and clarity,” he said.

The sketch is being sold in New York on 2 May and is the first time a work by Mandela has appeared at auction in the US.

“We have great hopes,” said Peppiatt. “We have an estimate of $60,000-90,000 but frankly I don’t know what it is worth – it is the kind of thing that could make three times that.

“The image is just so extraordinary. If it was a vase of flowers or a landscape in South Africa no one would be too fussed, but this is his cell door.”

Mandela retired as president of South Africa in June 1999. Like many retirees, he took up art.

It was a way of “expressing himself or coming to terms with his history … just coming to terms with his whole life”, said Makaziwe.