Around 1913 Henri Matisse seemed to be at the top of his game. In his mid-40s he was, at last, an international star, despite American critics who pronounced his new brand of modernism coarse or vulgar because, they said, he made naked women seem beastly. Having returned to Paris from Morocco in spring 1913, he began creating paintings that were simpler and more layered than the boldly colorful, sun-filled canvases that had been his signature. At the same time he started dipping his toe into Cubism, which was in full flower with younger artists like Juan Gris, Georges Braque and, of course, Pablo Picasso, whom Matisse began to see a lot during those years. While he admired Cubism for its inventiveness, the more instinctive Matisse was also suspicious of its intellectual emphasis. At the same time he also admired the work of Paul Cezanne -- in particular his carefully constructed compositions -- as Matisse began to reconsider his own working methods and fundamental ideas about making art. The years that followed proved to be a time of enormous change for Matisse. With life in Paris made difficult by World War I, he started experimenting with neutral shades, in particular blacks and grays, as well as with geometric shapes and daringly austere compositions. By 1917, however, he had moved to Nice and re-emerged as another kind of painter, abandoning the Cubist approach and adopting a style closer to Impressionism, painting soft women in cozy interiors as well as smaller, almost romantic canvases, now rendered through a harder, more modernist and reductive lens. 'He felt he'd done what he set out to do and thought it was crucial to keep changing,' said John Elderfield, chief curator emeritus at the Museum of Modern Art. 'He didn't want to become a prisoner of that style.' Although art historians could always track the changes of that period by studying his paintings in progression, one by one, until recently they had no clear idea of exactly how those changes were developed: how much hands-on experimenting went into the new work and what formal processes of study, revision and rejection were involved. Now those mysteries have been largely solved, thanks to an extraordinary array of technologies deployed in putting together 'Matisse: Radical Invention, 1913-1917,' an exhibition that opens next week at the Museum of Modern Art. The show offers a rare opportunity to look beneath the surface of Matisse's work to see a creative evolution that until now only his eyes had witnessed. The exhibition's organizers, Elderfield and Stephanie d'Alessandro, the curator of modern art at the Art Institute of Chicago, where the exhibit was first shown, focused on 26 paintings, drawings and sculptures, which they examined with new digital imaging techniques, laser scanning, ultraviolet illumination and up-to-date computer software. They also tested paint samples and studied fresh material unearthed from the artist's family archives in Issy-les-Moulineaux, a Paris suburb. D'Alessandro and Elderfield got the idea for the show after they started examining 'Bathers by a River,' which Matisse worked on from 1909 to 1916; it is a jewel of the Institute's collection. 'Matisse said it was one of the most pivotal works in his career,' D'Alessandro said in an interview. 'By studying the painting in depth,' she explained, 'we began to see a new chronology that hadn't been seen before, one which explained what he meant by that statement.' For one thing the curators could see changes in the outlines of figures beneath the painting's surface, revealing a constantly shifting landscape of figures, with stronger lines and more intense tones over time. 'We were never sure' of the degree to which 'he transformed the canvas,' Elderfield said. 'He kept going back. Yet he always stopped before a work looked finished.' Before they turned to high-tech analysis, the conservators removed the varnish and previous restorations from 'Bathers, 'which had yellowed over the years, obscuring the artist's palette; as a result, the colors came through more brightly. (They ended up removing the varnish from 20 of the 40 paintings in the show.) In addition to their work with the paintings, the curators unraveled the steps that had gone into the making of a suite of four large-scale relief sculptures depicting the back of a woman inspired in part by 'Three Bathers,' a Cezanne painting owned by Matisse. The sculptures, which he began around the time he was working on 'Bathers' and developed over 23 years, also grew more and more radical over time. Using laser scanning, they better understood how the process that went into the sculptures' evolution. The first, depicting a classical, round female body, was made in clay and then he cut two casts in plaster, one to make in bronze, the other to use as a starting point for the next sculpture. The scanning showed exactly how he used a cast from the previous sculpture for each of the four works, changing the surface of each succeeding figure until the overall form had a flatter surface and was quite stark and architectural, strikingly similar to many of his paintings during the same period. 'Like 'Bathers' it's one conception being evolved over all these years,' Elderfield said. Ultimately the curators were able to chart the course of Matisse's thinking as he added or subtracted details, scraped and rescraped the surface with a knife, moved objects from one side of a canvas to another, sharpened lines -- and juggled several works at once, borrowing from one, experimenting with another, never quiet satisfied. The result is a far more complete portrait of the artist during one of the least understood, yet critical, periods in his life. 'It really showed us,' Elderfield said, 'what it was like to make these works at this time.' 