Degas, uncovered: Exhibition shows artist's hidden images

The distinctive images of stretching ballerinas and women bathing in domestic settings have become recognisable as signature pieces of Edgar Degas' artistic legacy. But the public can now glimpse some of the images which lie beneath the surface of his celebrated paintings.

The distinctive images of stretching ballerinas and women bathing in domestic settings have become recognisable as signature pieces of Edgar Degas' artistic legacy. But the public can now glimpse some of the images which lie beneath the surface of his celebrated paintings.

An exhibition featuring 14 of his major paintings, Art in the Making, has used infra-red photography, x-rays and sketches to piece together impressions of how the master painter's works may have looked in his studio before the final, familiar versions were unveiled to the public.

In one instance, Degas is revealed to have sought the help of an anonymous draftsman who has not been credited for his collaboration in the artist's masterpiece, Miss La La at the Cirque Fernando . An x-ray shows Degas had great difficulty in sketching the complex lines of an octagonal room in which the acrobat, Miss La La, is shown dangling on a rope. So he commissioned the help of an architectural draftsman and used his sketch as a guide to complete the work. He later admitted to his friend and painter, Walter Sickert, that he had hired the draftsman.

The exhibition, opening at the National Gallery today, reveals how Degas achieved his visual effects through experimental techniques. Charles Saumarez Smith, the gallery's director, said the collected paintings - including two on loan - along with sketches and infrared images, have been brought together for the first time to "yield a very rich understanding of Degas' works of art".

Christopher Riopelle, the exhibition's joint curator, said the technology also allowed viewers a far more intimate glimpse at Degas' thought processes. "The infra-red photography offers us a return of the repressed, all that lies underneath the surface image," he said.

Degas' work was originally due to feature in an exhibition on Impressionists 14 years ago but experts felt a solo display was required because of the complexity of his techniques. The technology shows how the artist returned obsessively to rework compositions he had finished years previously and expanding paintings by adding on extra paper. David Bomford, one of the co-curators, said Degas' friends had resorted to chaining down the paintings he had given them due to his tendency - especially in later years when his eyesight was weakening - to borrow his own works so he could alter them.

An infra-red image of the painting, Beach Scene , which features a girl in a reclining chair having her hair brushed, shows how he attached three pieces of paper together to complete the picture, which began with just a simple image of the young girl.

In another instance, an x-ray of a portrait of Degas' cousin, Elena Carafa , reveals the model's facial expression and positioning was changed in the painting process. The lines beneath the surface show the model staring dreamily into the distance but in the final version she in looking inquisitively at the painter.

The technology also solves the mystery of why Degas may have abandoned an early 1860 version of Young Spartans , which he intended for the Salon but discarded abruptly without finishing it. He later produced a small oil sketch of a similar scene, Young Spartans Exercising, which he then used as the basis of a bigger version, whose ultra-red image shows him to have changed aspects of the work over three decades, superimposing the faces of Parisian street urchins on the Spartans and removing the temple which features at the centre of the abandoned version.

The show, sponsored by ExxonMobil, is the fifth in the series and runs until 5 January 2005.