These color postcards of the sun-baked streets and Moorish architecture of Tunisia were created using the Photochrom process, a technique for applying realistic color to monochrome images that predated the spread of practical color photography.
Invented by a Swiss printer in the 1880s, the process began with coating a tablet of lithographic limestone with a light-sensitive emulsion, then exposing it to sunlight under a photo negative for up to several hours.
The emulsion would harden in proportion to the tones of the image and the less-hardened portions would be removed with a solvent, leaving a fixed lithographic image on the stone.
Following detailed notes on color made by the original photographer, additional litho stones would be prepared for each tint to be used in the final color image — often more than a dozen stones for a single postcard.
When completed, the delicate process produced surprisingly lifelike color with far greater precision than traditional hand-coloring.
These images capture the ornate palaces and bustling markets of Tunisia in its first decades as a French protectorate.