The Autochrome Lumière was an early color photography process patented in 1903 by the Lumière brothers in France and first marketed in 1907. Autochrome was an additive color "mosaic screen plate" process. It was the principal color photography process in use before the advent of subtractive color film in the mid-1930s.
Prior to the Lumière brothers, Louis Ducos du Hauron utilized the separation technique to create colour images on paper with screen plates, producing natural colours through superimposition, which would become the foundation of all commercial colour photography. Descendants of photographer Antoine Lumière, inventors Louis and Auguste Lumière utilized Du Hauron's (1869) technique, which had already been improved upon by other inventors such as John Joly (1894) and James William McDonough (1896), making it possible to print photographic images in colour. One of the most broadly used forms of colour photography in the early twentieth century, autochrome was recognized for its aesthetic appeal.
Structure and use
Autochrome is an additive color "mosaic screen plate" process. The medium consists of a glass plate coated on one side with a random mosaic of microscopic grains of potato starch dyed red-orange, green, and blue-violet (an unusual but functional variant of the standard red, green, and blue additive colors); the grains of starch act as color filters. Lampblack fills the spaces between grains, and a black-and-white panchromatic silver halide emulsion is coated on top of the filter layer.
Unlike ordinary black-and-white plates, the Autochrome was loaded into the camera with the bare glass side facing the lens so that the light passed through the mosaic filter layer before reaching the emulsion. The use of an additional special orange-yellow filter in the camera was required to block ultraviolet light and restrain the effects of violet and blue light, parts of the spectrum to which the emulsion was overly sensitive. Because of the light loss due to all the filtering, Autochrome plates required much longer exposures than black-and-white plates and films, which meant that a tripod or other stand had to be used and that it was not practical to photograph moving subjects. The plate was reversal-processed into a positive transparency — that is, the plate was first developed into a negative image but not "fixed", then the silver forming the negative image was chemically removed, then the remaining silver halide was exposed to light and developed, producing a positive image.
The luminance filter (silver halide layer) and the mosaic chrominance filter (the colored potato starch grain layer) remained precisely aligned and were distributed together, so that light was filtered in situ. Each starch grain remained in alignment with the corresponding microscopic area of silver halide emulsion coated over it. When the finished image was viewed by transmitted light, each bit of the silver image acted as a micro-filter, allowing more or less light to pass through the corresponding colored starch grain, recreating the original proportions of the three colors. At normal viewing distances, the light coming through the individual grains blended together in the eye, reconstructing the color of the light photographed through the filter grains.