The Chemistry of . . . Photography

Has anyone changed the world as utterly and gotten as little credit for it as Joseph-Nicéphore Niépce? People with any notion at all of who invented photography usually think it was that other Frenchman, Daguerre— he of the daguerreotype— but Daguerre got the idea from Niépce. Niépce's camera was a cubical wooden box, about a foot on a side; his film was a tin or stone plate coated with asphalt, which hardened where the light struck it. With this unlikely apparatus Niépce took the world's first photographs, in 1824, from a window of his manor house in Burgundy, at a time when Daguerre was still painting theater sets. The results, judging from the one image that survives, were surprisingly sharp: Far across the courtyard, behind the dovecote, you can make out a pear tree with a gap in its foliage. "Even though it was asphalt, it's still the ancestor of all the processes we use today," says Jacqueline Belloni, a physical chemist at the University of Paris-South at Orsay. "Everything was already there." That makes photographic film sound a bit like a Flintstones relic, what with cameras going digital and darkrooms giving way to computers. Far from it: Even a $10 single-use camera offers 10 times better resolution than today's $1,000 digital— and thanks to Belloni, that gap is likely to widen. In the late 1980s, Belloni helped elucidate the fundamental chemistry of film developing. Now she has developed a new method of "doping" film emulsions that promises to make them five times better at capturing light. "If it can be widely applied," says chemist Rolf Steiger of Ilford, a film manufacturer, "it will certainly be one of the greatest inventions in photography in the last 60 years." Ever since Daguerre (give him credit too), the crucial light-sensitive material in photography has been silver halide. Film is basically a lot of silver halide crystals suspended in gelatin on a plastic backing. When a camera's shutter opens, light photons stream through the lens, fall on some of the crystals, and dislodge electrons from the halide ions. Some of the electrons glom onto nearby ions of silver, converting them to neutral atoms. The atoms then cluster together, forming a tiny black speck of metallic silver on each exposed crystal. Millions of such specks form the image. But to make the image visible, even to a microscope, a photographer has to wash the film in a chemical developer (another contribution of Daguerre's), which finishes the work the light started.