Image: Library of Congress
These postcards of the sweeping hills, cliffs, and towns of Ireland were created using the Photochrom process, a complex method of imbuing black-and-white photographs with relatively realistic color.
The closely-guarded process was invented in the 1880s by an employee of a Swiss printing company. It entailed coating a tablet of lithographic limestone with a light-sensitive emulsion, then exposing it to sunlight under a photo negative.
After several hours, the emulsion would harden in proportion to the tones of the negative, leaving a fixed lithographic image on the stone. Read more...
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