By Natasha Gural
The Associated Press

From simple pen and ink drawings of nude women to a colorful and elaborate felt pen and ink drawing of two men ogling a nude woman, a sketchbook that was filled in a week reveals the obsessive nature of a mature Pablo Picasso at work.

The 26 works from a 1970 album of drawings and watercolors are on public display for the first time ever, offering an intimate look into the art and thoughts of Picasso, less than three years before his death at age 91.

Picasso: The Berggruen Album, opened Monday at Mitchell-Innes & Nash gallery in New York, in cooperation with John Berggruen Gallery in San Francisco, and runs through June 26. The full book from the collection of art dealer Heinz Berggruen was carefully unbound for framing, and will be reassembled for sale at $3.5 million. Such sketchbooks are very rare, as most belong to the Picasso family, gallery owner David Nash said.

Picasso created sketchbooks throughout his life. But these drawings are works "of a very personal nature," said Olivier Berggruen, an independent scholar and the youngest son of Heinz Berggruen. "It also gives a very good idea of his day-to-day thinking. You have this kind of intimacy."

"Reclining Nude," a pen and ink on paper is the simplest of the works, with delicate yet clearly defined lines. It is reminiscent of Picasso's 1906 gauche and watercolor of the same name.

On the same day, Nov. 5, 1970, Picasso used a light touch with pen and ink for the outline of "Two Men and a Woman." On Nov. 12, he revisited the work with felt pen to create the busiest and only multicolored page in the album.

Nude women are a common thread in the drawings, most of them highly sexual and offering themselves to men, which is typical of Picasso's late work, Olivier Berggruen said.

Picasso created the 26-page album over the course of seven days while at his home in Mougins, France. He produced approximately four works per day, varying his medium from pen and ink to pencil, ink wash and watercolor. Picasso biographer John Richardson has suggested that the album makes references to the work of Ingres and Goya, and that some of the female figures depict the artist's wife, Jacqueline.

"I think the interesting thing is the sequence," Nash said. "Picasso very carefully annotated and dated each work."

Heinz Berggruen collected works by Picasso, Klee, Braque, Cezanne, Giacometti, Matisse, Seurat and van Gogh.

In 1996, a part of his collection was set aside to form one of Berlin's most important museums of modern art, the Sammlung Berggruen. A year later, he donated 90 paintings by Klee to the Metropolitan Museum of Art.