How did dyed potato starch make the first practical colour photographs?
Before colour film, the Lumière brothers scattered millions of dyed potato-starch grains on glass and let each one filter the light.
▶ Start the storyThe first colour photographs did not capture colour so much as sort it. In 1855 the physicist James Clerk Maxwell proposed that any colour of light can be made by mixing red, green and blue. So take three black-and-white photographs of the same scene through red, green and blue filters, project them through the same filters, and the colours of the original scene reappear.
The first photograph made this way, by Thomas Sutton in 1861, was a ribbon bow. It probably worked by luck: his process was practically blind to red, and a century later researchers found that the "red" picture probably came from ultraviolet light that many red dyes reflect. The method also had a weakness. If the three exposures were not made at the same moment, anything that moved showed coloured fringes. Prokudin-Gorsky still crossed the Russian Empire with it between 1909 and 1915, in a railway-car darkroom provided by the Tsar.
The Lumière brothers took a cleverer route. Their Autochrome plate, marketed in 1907 and the first commercially successful colour process, was a sheet of glass coated with a random mosaic of microscopic potato-starch grains dyed red-orange, green and blue-violet, with a black-and-white emulsion on top. The grains acted as filters, so one exposure sorted the light into three colours by itself, and the plate was developed into a positive transparency. Seen at normal distance, the grains blend in the eye, and the colours come back.
Step 1: Dyed starch grains
Red-orange, green and blue-violet, scattered at random on glass
Step 2: Black-and-white emulsion on top
Light reaches it only through the grains
Step 3: Reversal development
The plate becomes a positive transparency
Step 4: Viewed with light behind
Each grain glows its own colour and the eye blends them
The price was light: all that filtering needed long exposures and a tripod. Even so, between 1909 and 1931 the banker Albert Kahn gathered 72,000 autochromes of life in 50 countries.
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Recap
Colour photography records three filtered brightnesses and lets the eye recombine them, whether through three exposures or a mosaic of dyed grains.
💡 A trick to remember it · Millions of tiny coloured sunglasses on one plate: each grain lets one colour through, and your eye does the mixing.
Surprising fact · Sutton's 1861 photograph shows red even though his process was almost blind to red, probably because of ultraviolet light.
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