The world’s first color photograph, shown above, is nothing fancy; the image looks like two color gradients made in Photoshop, plastered to a silver plate. But the story behind the peculiar image, which shows two strips in varying shades of purple, goes much deeper than you think.
The color photograph dates back to 1848, when the French physicist Edmond Becquerel first created it at the Muséum d’Histoire Naturelle in Paris.
Becquerel’s method in producing the photograph was more empirical than artistic in nature, decidedly unpopular, and, as the French National Centre for Scientific Research puts it, “quickly abandoned.”
Plus, Becquerel made very few images, and the ones that did remain “quickly faded under daylight,” according to a passage in the 2014 book Exploring Color Photography: From Film to Pixels.
For those reasons, nobody ever really understood how he created the image for the last 172 years—until now.
Researchers at Le Centre de recherche sur la conservation, in collaboration with SOLEIL synchrotron—a particle acceleration facility—and the Laboratoire de Physique des Solides, have recreated Becquerel’s process to make samplings of different colors. The team began by re-examining 19th-century hypotheses on how he made the images, but with knowledge of 21st-century tools.
The scientists knew, for example, that if the colors were created when pigments formed during a reaction with light, there should have been variations in chemical composition from one color to another. Modern-day spectroscopy methods showed no deviations.
If purplish hues in the photograph were the result of interference—when two waves come together to form a new wave with a new amplitude, as in some butterfly wings—the colors in the image should have shown microstructures that were about the same size as the wavelengths for the corresponding colors. Yet electron microscopy proved there were none.
Becquerel’s image depicts the solar spectrum, a continuum of various electromagnetic waves that make up the energy in solar irradiation. Longer wavelengths, such as infrared waves, have less energy than shorter waves, like ultraviolet or visible light. Becquerel called the photographs “photochromatic images.”
Becquerel wasn’t really a photographer by trade. Instead, we mostly know him for his discovery of the photovoltaic effect, which proves materials exposed to light can generate voltage and an electrical current. It’s the underlying principle for today’s solar cells. And if the last name sounds familiar, he’s also the father of Henri Becquerel, one of the discoverers of radioactivity.
It wasn’t until these scientists examined the colored plates closely that they discovered how Becquerel made the images: He hid metallic silver nanoparticles inside the matrix of the silver chloride grains in the silver plate used to capture the image. These nanoparticles are photosensitive, resembling the silver chloride contact printing paper still used in today’s darkrooms.
The researchers assumed that based on the light’s color (and therefore, its energy), the distribution of sizes and locations of the silver nanoparticles on the silver plate varied. Where the color red may appear, there’s a different scattering of silver nanoparticles than, say, where the color blue may appear. In this way, the plate could absorb all colors of light, with the exception of the color that actually caused it: the one we see.
So now the case is closed—and it may be the most meta solution possible. Becquerel made his image of the visible spectrum by exposing a silver sheet to the visible spectrum.