Magritte on Magritte: letters reveal surrealist Damien Hirst

René Magritte's instructions to New York dealer – illustrated with bowler-hatted man motif - show a modern eye for

A rare collection of unpublished letters from Rene Magritte to his art dealer in New York A rare collection of unpublished letters from René Magritte to his art dealer in New York, Alexander Iolas, is being prepared for auction by Marsha Malinowski of Sotheby's. Photograph: Sarah Lee for the Guardian

Unpublished letters that cast fresh light on one of the most accomplished, least eccentric and – it turns out – most entrepreneurial of all the surrealist artists, René Magritte, are to be sold at auction.

The precisely written letters, complete with more than 40 drawings are, according to the auction house Sotheby's, excessively rare and reveal an artist who exercised huge control over every aspect of his work. He was, it seems, as concerned by the marketing of his art as he was by the paintings themselves.

The letters also include famous Magritte motifs, some of which can be seen for the first time in the documents for sale, including the faceless character who appeared in his painting Le Liberateur, and the chair upon a chair in La Légendes.

Magritte's letters are not being sold until June, but have been rushed from New York to London to go on display with five works by the artist that are being sold on Tuesday in a sale of post-impressionist and modern art.

Sotheby's book and manuscripts expert, Marsha Malinowski, said they were nothing short of extraordinary. "Magritte letters are just very hard to find and to have them with so many drawings of his iconic images is extremely rare."

The letters have been in the hands of an American collector for at least 20 years. They are from Magritte to his dealer in New York, Alexander Iolas, a one-time Greek ballet dancer, and all are written in very clear and precise handwriting.

They relate to exhibitions being held in Iolas's galleries and the level of detail is striking.

Magritte had instructions for everything: what should be shown, where, how they should be framed, what text to use in the catalogue, and so on.

Magritte comes across as a forerunner of the likes of Damien Hirst, who also has as keen an eye on marketing as he does on the art. The two also have their own motifs, which they use over and over again in their works.

"What's really fascinating with these letters is that you can clearly see the juxtaposition of Magritte as the artist and as the businessman," said Malinowski. "Magritte is not only doing the works of art, he's doing his own marketing, which is just incredible for an artist. Magritte was such an entrepreneur on so many different levels."

Magritte was never a starving artist; he always had a firm business head on his shoulders and these letters attest to that. "He was very grounded and a very hard worker," said Malinowski. "So many people think the surrealist movement was kind of out there and flakey, but Magritte went to Paris and studied with the surrealists, then went back to Belgium because he didn't like the drugs, he didn't like the drinking. He wanted to do his work."

In the letters Magritte talks about how he tries to put his ideas on paper.

The letters, which will be sold in New York with an estimate of $150,000-$250,000 (£93,000-£155,000) are all unpublished and amount to 42 pages – including 40 drawings. They contain some of Magritte's most instantly recognisable motifs, including his most famous, the bowler-hatted man.

A bowler-hatted man will also be among the Magritte works being sold at Sotheby's on Tuesday: the gouache Le Maître d'école, in which the man stares up at a crescent moon in a wonderfully darkening blue sky, will be sold with an estimated price-tag of £800,000-£1.2m.

Auction houses Christie's and Sotheby's will both stage big London sales this week. It was this time last year that a world record art auction price was set for a Giacometti Walking Man, sold for £65m.

Highlights of this week's sales include a Gauguin sunflower still-life, painted as a tribute to his friend Van Gogh, and a Picasso portrait of his mistress and muse, Marie-Thérèse Walter.

Flight to quality

The middle may be squeezed, but the buyers at the top of the tree, particularly from China and Asia, have barely been affected by the economic gloom. Both Sotheby's and Christie's say the buyers are still there for works of exceptional quality.

The two auction houses are mounting big sales of 20th century and impressionist art this week, including works by Picasso and Gauguin, with Christie's hoping to take up to £81m on Wednesday alone.

Christie's reported international sales were up by 53% last year, to a record £3.3bn, with the contemporary art market particularly strong. Sotheby's last month set a new record for a work by Titian, when his Sacra Conversazione sold for almost $17m in New York, and in December it saw a world record for any book, when Audubon's Birds of America went for more than £7m, £1m over the top estimate. Maev Kennedy