Color capture has been an essential technology for fifty years, critical for the adjustment of the color of the urban sky.

The first CoCap devices were designed by Hitachi in 1971, as part of a project to curb a decade of unremitting air pollution in the coastal city of Yokkaichi. Efforts to address chronic air and water contamination required the abatement of sulfur dioxide, produced during the combustion of fossil fuel, as well as the toxic cadmium compounds that were a byproduct of fertilizer production. As pollution was gradually brought under control, scientists observed an unexpected purpling of the skies, caused by an absence of the airborne yellow pigment cadmium sulfide that had been formed as a compound of these two contaminants. A presentation in Stockholm at the 1972 United Nations Conference on the Environment revealed similar conditions around the world: the abatement of mercury was suppressing the natural vermillion of mercury sulfide, slowly greening the skies of the Great Plains states; a reduction in cobalt was removing the cerulean cobalt sulfate from Central America. The burgeoning low-salt diets of the 1970s had produced a marked drop in sodium production, and the consequent shortage of atmospheric sodium sulfate had begun to eliminate ultramarine from skies across the Northern Hemisphere.

Rooftop CoCap machines like these are hybrid systems, simultaneously collecting and storing unwanted pigments, and aerosolizing desirable coloration into the lower atmosphere. A fixture of the industrial world for half a century, color capture has become not only the technology that assures our beautiful skies, but a critical source of income for nations that participate most fully in the international marketplace for color offsets (ChromeX).

Published January 15, 2023. Copyright © 2023 Jonathan Hoefler.