When David Hockney visited a 1999 exhibition at London's National Gallery of paintings by the early 19th-century French neoclassicist Jean-Auguste-Dominique Ingres, the uncanny accuracy of Ingres's portraits startled him. He began to wonder: Had Ingres used some sort of optical aid to render minute facial features so precisely? Hockney subsequently examined paintings by other masters and surmised that artists began using rudimentary forms of optical devices as early as the 15th century, nearly 200 years before Galileo and the emergence of the telescope.
In his new book, Secret Knowledge: Rediscovering the Lost Techniques of the Old Masters, Hockney explores the revolutionary implications of his theory. The early use of optical aids by artists—earlier, even, than their use by scientists—could account for the sudden, dramatic improvements in the rendering of perspective and proportion and for the remarkable transformation in the realistic appearance of portraits that occurred at the beginning of the 15th century. Some art mavens have scoffed at the idea that the genius of some Renaissance masters may have been augmented by rudimentary optical technology. But Hockney has diligently amassed an impressive body of scientific, as well as historical, evidence to support his case.
To test his theory, Hockney solicited the help of physicist Charles Falco, a professor of optics at the University of Arizona, who systematically analyzed key measurable distortions in early paintings. "The images themselves are the evidence, if you know how to read them," says Falco. For instance, in Lorenzo Lotto's late Italian Renaissance painting Husband and Wife (circa 1543), the geometric pattern of the tablecloth loses focus as it recedes into the painting, and oddly, there are two vanishing points clearly visible in the detail of the fabric's border. "Had linear perspective been used, the pattern would have receded in a straight line, the single vanishing point corresponding to a single viewpoint," says Hockney. Instead, there is a kink in the pattern, which then continues in a slightly different direction. Hockney and Falco concluded that Lotto had used some sort of lens to project and trace the pattern of the cloth but then found he could not keep it all in focus at the same time; so he refocused the lens to complete the back portion of the cloth, changing the vanishing point, which he painted "out of focus" in an attempt to camouflage the process.
The earliest evidence of the use of optics that Hockney and Falco have discovered is in a 1431 sketch and portrait of Cardinal Niccolò Albergati by the Flemish artist Jan van Eyck. The subject's facial features are perfectly rendered. And although the finished painting is 41 percent larger than the sketch, when the latter is enlarged and laid over the painting, many key features line up exactly: forehead, right cheek, nose, mouth, eyes, and even laughter lines. Falco insists that to have scaled up the sketch so precisely, Van Eyck must have used an optical aid.
So what kind of optical devices did these early artists use? Later paintings offer some clues. The seemingly photographic manner in which the Dutch painter Jan Vermeer (1632-1675) recorded the soft play of daylight on various shapes and surfaces has prompted many art historians to speculate that he used a camera obscura. In its simplest form, this device is nothing more than a small hole in a shade or wall, through which light passes from a sunlit garden, for example, into a dark room, projecting an inverted image of the scene onto the wall opposite the hole. An artist could easily tack a piece of sketch paper to the wall and trace the key outlines of the subject, then complete the painting from life. Hockney suggests that Ingres (1780-1867) most likely used another innovation, the camera lucida, which consists of a prism mounted on a stick that can be attached to a drawing table. The camera lucida is more portable than the camera obscura and allows the artist to work in direct sunlight as opposed to a darkened room. However, it is notoriously difficult to use, since it doesn't actually project an image of the subject onto paper; the image seems to appear on the drawing surface only when the artist looks into the prism. A slight movement of the head will cause the image to move also, disrupting the accuracy of the tracing.
