In the 1960s, a French artist named Jean-Pierre Sudre began experimenting with an obscure 19th-century photographic process, creating dramatic black-and-white photographs with ethereal veiling effects. Sudre christened the process "mordanҫage," the French word for "etching." Since then, other photographers have used and refined mordanҫage to create unique works of art. Now, researchers reporting in the ACS journal Analytical Chemistry have unveiled the mysterious chemistry behind the process.