One benefit of being among history’s greatest artists is that if you don’t much like a painting done by someone else, you can just improve it. The Flemish master Sir Peter Paul Rubens certainly knew how to paint people; Rubenesque is still used to describe a curvaceous, ample body. So when he noticed the inferior quality of the religious figures depicted on an otherwise accomplished landscape hanging on his wall, it turns out he simply picked up his paint palette. A newly rediscovered Herri met de Bles painting, titled The Holy Family with the Infant Saint John the Baptist in an Extensive Landscape with Travellers, set a puzzle for art historians because the style of the landscape background did not match the group of people. Hi-tech imaging of the canvas carried out by a London auction house has since “completed the jigsaw”, revealing the way Rubens had tinkered with a painting now thought to have belonged to his own collection. “Rubens must have thought it would be fun to repaint it,” said George Gordon of Sotheby’s Old Masters. “He would have recognised it was a pretty good work by Herri met de Bles, but then noted that the stiff human figures had probably been painted by someone junior in his workshop, or even down the street in a neighbouring workshop.” Now, when the work comes up at an Old Masters auction at Sotheby’s on 3 July, with a reserve value of between £600,000 to £800,000, it will be ascribed both to the admired landscapist De Bles and to Rubens. De Bles, who lived in the first half of the 16th century, was known by the nickname il Civetta, the Italian for little owl; he signed his canvases with an owl symbol, in this case inside the cage carried by one of the tiny distant travellers. But the image of the holy family and the infant John the Baptist will be properly attributed to Rubens. “We know Rubens did the occasional overpaint on an old master canvas. It started with retouching drawings and sometimes painting copies of other works, but in his own style,” said Gordon. “He was fascinated by the art of the past and saw himself as continuing a tradition. In his own work he drew on earlier masters and then completely transformed these sources into his own manner.” Infrared photography and X-rays carried out before the sale have revealed that Rubens reworked the positions of the baby Jesus, as well as of John the Baptist, and made the folds of the drapery around the Virgin Mary more luxuriant. “We did an X-ray,” said Gordon, “but it was the infrared image that was really helpful in showing us the underdrawing of the figures. It is so interesting to work out what he did. It completes a jigsaw puzzle.” Auction catalogue notes point out that Rubens’s changes make the image less formulaic and so more dynamic. The figures were altered to interact with each other more intimately, drawing the eye. The X-rays reveal two heads of Christ looking in different directions and show the alterations made to the legs of St John the Baptist. The infrared exposes the original underdrawing of the composition. Rubens clearly focused on what he saw as the weakest parts of the work, leaving alone the figure of Joseph and the landscape. Just as importantly for Sotheby’s, the research offers new evidence the picture was once in Rubens’s possession, since he is unlikely to have taken such a liberty with someone else’s property. “It is likely to have been in his collection,” said Gordon. “The inventory of Rubens’s art and possessions that he left when he died at 62 in 1640 is infuriatingly vague.” In other cases where Rubens reworked paintings, or more usually drawings, they were damaged works or pictures of lesser quality. Art historians are not sure if he intended to make them more saleable in the thriving, cosmopolitan art market of Antwerp. The artist’s early biographer, Roger de Piles, believed it was a mainly creative exercise, done “to stimulate his senses and to heat up his genius”. Gordon sees Rubens as “a restless polymath”, someone who is famously described as dictating letters in several languages to different scribes, while he painted at his easel and also listened to music. And Sir Joshua Reynolds, the 18th-century portrait artist and co-founder of the Royal Academy of Arts, clearly approved of Rubens’s habit of reusing and restyling, once writing: “What was stolen by Rubens, the possessor knew not how to value; and certainly no person knew so well as Rubens how to use.”