These postcards of New York City at the turn of the 20th century were produced by the Detroit Publishing Company using the innovative Photochrom process to add precise gradations of artificial color to black and white photos.

Invented in the 1880s by an employee of the Swiss printing company Orell Gessner Füssli, Photochrom was an exacting and time-consuming process. It involved the creation of a lithographic stone from the photo negative, followed by the successive creation of additional litho stones — one for each tint to be used in the final image.

More than a dozen different tinted stones might be involved in the production of a single image, but the result was remarkably convincing color at a time when true color photography was still in the earliest stages of development.