Autochromes: one-shot colour process
The autochrome was the first truly viable and successful method of producing a one-shot colour image on a single plate in virtually any camera. In so doing, it revolutionised colour photography up to that point. The process was the brainchild of two French pioneering photographic equipment manufacturers, Auguste and Louis Lumière, who first presented their researches into colour photography to the French Académie des Sciences in 1904. The autochrome process was patented in 1907, the year the first public demonstration took place at the offices of the French newspaper L’Illustration.
Manufacture of autochrome plates took place at the Lumière factory in Lyon. It began with transparent grains of potato starch, passed through sieves to isolate the very smallest, measuring between ten and fifteen microns (thousands of a millimetre). Once isolated, the tiny grains were divided into three groups, which were dyed red, green and violet. Once dry, they were thoroughly mixed together. A glass plate was next coated with a sticky varnish and onto this the potato starch grains were spread at random, about four million grains to the square inch. Charcoal powder was used to fill in any gaps and the whole thing submitted to high pressure under a roller to flatten the grains. Finally, a panchromatic photographic emulsion was applied over the top of the grains.
Autochrome plates were placed into a camera with the potato starch layer facing the lens, so that light had to pass through the particles to reach the emulsion. A yellow filter was placed over the lens to correct the excessive blue sensitivity inherent in emulsions of the day. The effect was much the same as when three different plates were exposed through three filters, the difference being that these filters, made up of the dyed potato starch particles, were extremely small and mixed together to record their individual and minute filtered light onto a single plate.
Because the emulsion was actually monochromatic, the autochrome could be treated in much the same way as a mono lantern plate was normally developed to make a positive image. When the positive monochrome image was viewed against a light source, the coloured potato starch grains, being too small to be individually identified, coalesced so that the filtered monochrome image was seen in full colour.
One problem encountered by autochrome users was a fault that occurred during processing when the emulsion separated from the edges of the glass plate, causing loose gelatine to swell, expand and crinkle. This was known as frilling. One way around that was to use a piece of apparatus such as the Campbell Anti-Frilling Dish which was made of wood and in two parts. One part contained a deep groove into which the autochrome plate was slotted. The second part contained a rubber cushion which held the plate tightly around its edges when the two halves of the dish were pushed together and held in place by clips on the edges. The plate itself then formed the bottom of the dish. Now when the chemicals were poured in to cover the plate, they were prevented from reaching its edges. There was a trough at one end of the dish to hold the liquid while the plate was examined, and a lip at the edge facilitated the easy pouring off of the chemicals.
It was possible to project autochromes using a magic lantern, but the images were dense and not entirely suited to projection. Autochromes could of course be viewed by simply holding them up to the light, but the plates were more often viewed by means of a device called a diascope. This generally comprised a simple folding wooden frame that hinged open to make a V-shape. The top of the outside edge of the frame contained a lipped aperture the size of a standard photographic plate, into which the autochrome was placed then covered by a hinged frame containing a sheet of ground-glass to diffuse the light. On the inside base of the viewer, there was a mirror that reflected the image of the autochrome above, lit by either natural or artificial light. In this way several people could view the image at the same time.
Although autochrome plates were difficult to manufacture, they were very easy to use and appealed to amateur as well as professional photographers. The images themselves often exhibited an attractive ethereal quality. By 1913 the Lumière factory was producing 6,000 plates a day in quarter-plate, half-plate and 5x4-inch sizes.
Autochromes were, however, expensive. In 1910 a box of four quarter-plate autochromes cost thee shillings (15p), against two shillings (10p) for a dozen more conventional monochrome plates. The way the dyed particles cut down light, so that only 7.5 per cent of the light reached the emulsion, also meant that exposures were a lot longer than for a monochrome plate. Nevertheless, autochromes continued to remain popular well into the 1930s.
Boxes in which autochromes were sold in different sizes of plates.
The dyes starch grains on an autochtrome plate, magnified 700 diameters
(From the book Photography in Colours, 1914)
Four autochromes: two half-plate, one quarter-plate and one 5x4in.
The Campbell Anti-Frilling Dish, used in the development of autochromes.
A half-plate size autochrome viewer and the way it was advertised in 1908. The autochrome is placed under the ground-glass screen, seen here in its raised position, the screen is lowered and the image is viewed in the mirror below.