These postcards of the windmills, canals and cities of the late 1890s Netherlands were created using the Photochrom process, a technique for applying lifelike color to black-and-white images.
Invented in the 1880s by Hans Jakob Schmid, an employee of a Swiss printing company, the process begins with applying a light-sensitive emulsion to a lithographic limestone tablet and exposing it to sunlight under a photo negative for several hours.
The emulsion hardens in proportion to the tones of the negative. The less-hardened portions are then removed with a solvent, leaving a fixed lithographic image on the tablet.
Additional litho stones are then prepared for each tint to be used in the final image — a single Photochrom might require over a dozen stones and hours of labor to produce.
Though painstaking and time-consuming, the Photochrom process was capable of creating remarkably precise color images at a time when true color photography was just starting to be developed.