Autochrome was the first popular colour process and proved an immediate success when put on the market in 1907. It used a mosaic screen composed of starch grains dyed red-orange, green and blue-violet in front of a fine-grain panchromatic emulsion. The need to use a fine-grain emulsion and the filtering of the screen resulted in a very slow plate having a speed of around 1 - 2 Watkins, 10 - 14 Wynne.

Autochromes were available in most sizes up to whole-plate. When introduced the cost of a box of four half-plates was 10/- this was reduced after a year or two to 7/6 (a dozen ordinary plates cost around 3/-). As well as Autochrome plates Lumière supplied the developer and other chemicals needed to process the plates and a paper, Virida, to be used as a safelight filter. For those not wishing to undertake the developing, firms, such as Sinclair, charged 1/6 to process a plate.

A popular way of displaying the images was with a viewer having a horizontal mirror which reflected the image of the Autochrome held in a frame at 45° to the mirror, cloth or wooden sides blocked out extraneous light. Other viewers used a mirror to reflect light onto the back of the Autochrome which was viewed directly from the front. Stereo Autochromes could be viewed in an ordinary stereo viewer but the image would be laterally reversed unless the plate was cut and the images transposed. Richard produced a viewer specifically for Autochromes with prisms behind the eye-piece that reversed the images. T.K. Grant, the London agents for Lumière, advertised stereo viewers for Autochrome with long-focus lenses.¹

Production of plates ended around 1932 with the introduction of Filmcolor, a celluloid based cut-film, in 1934 Lumicolor roll-film was introduced.

Outline of the process

• The photograph is taken in the normal way except that the plate is reversed with the emulsion furthest from the lens so that the light passes through the coloured screen. To focus it was common to reverse the focusing screen to compensate for the reversed plate.² If a light filter was used behind the lens the camera could be focused without the filter, positioning the filter behind the lens then compensated for the thickness of the plate. Zeiss produced filters - Ducars - incorporating a negative lens that displaced the image, the filter was fitted to the front of the lens after focusing. On some cameras, such as the Verographe, there was a separate focusing scale for Autochrome. Special dark-slides were later sold with a layer of black card or velvet which pressed against the emulsion.

  The image on the right shows the two focusing scales on a Verographe camera.

  A yellow filter was used on the lens as the plate was over sensitive to blue (this was the case for all panchromatic emulsions of the time). Exposure meters came to be marked with a setting for Autochrome and dedicated meters were produced by manufacturers such as Watkins.³

  The image on the right shows filters for the Autochrome process. The round filter is a Zeiss Ducar which incorporating a negative lens that displaced the image, which was useful on cameras without focusing screens, it was fitted to the front of the lens after focusing.

• The plate is developed as normal; Autochrome developer was sold as Quinomet (Metol Hydroquinone).⁴ At the time panchromatic plates were little used and the requirement to process the plate in total darkness, or at best using a very dark safelight, would have been new to many photographers. A darkroom timer fitted with a bell was produced to time the first development of the plate rather than holding the plate up to a safe-light. A greenish tint resulted from the plates being loaded or processed in an unsafe light. Frilling at the edges was common, gum was sometimes applied to the edges of the plate during processing or a special developing dish could be used fitted with a removable inner tray that prevented the developer reaching the edges of the plate.
• The negative image was then dissolved with a permanganate solution. The plate was exposed to white light which acted on the previously unexposed silver halide and was then developed for a second time and fixed. A clearing bath was sometimes used to enhance the colours. The plates were varnished or bound as lantern slides.

Manufacture

The dyed grains were dusted on to a glass plate having a tacky coating, loose grains were removed by brushing. The plate then passed under a roller to flatten the grains which tended to close the gaps between them, any remaining gaps were filled with fine black powder. The intended size of the grains was 0.01 - 0.02 mm, but in practice the variation was larger. With only three colours, the screen suffered from the purely statistical problem of 'clumping' where several grains of the same colour would lie next to each other forming a larger patch of colour.

Patents

Thefirst British patent was dated 1904, in France it had been submitted the year before. The first patent proposed that the plate be coated with grains coloured red, yellow and blue, the plate was then again coated with a tacky layer followed by a second coating of grains of the same colour, these would overlap in places producing a screen of six colours - red, yellow, blue, orange, green and blue-violet. The second patent of 1904 proposed a single coating of grains but of multiple colours. The 1906 patent referred to the grains being flattened by rolling. The patents refer to grains but also mention other substances that could be coloured and remain transparent. A series of patents was issued between 1909 and 1911 covering the production of other types of coloured screens.

Multi-colour Screen Photography

Additive three-colour photography entailed making three separate exposures through three coloured filters (usually red, green and blue), the images were then combined on a projection screen or in a viewer. With a multi-colour screen the colour filters are reduced to microscopic dimensions and placed immediately in front of the emulsion. A single exposure therefore records the red, green and blue images on a single plate. In itself this was an easier process to use and, in addition, required little or no special equipment either when making the exposure or when viewing the image.

There were two types of screen, one used a regular pattern of lines and squares, to form the filters, the other used a random arrangement of coloured dots. Regular screens were often brighter as the whole plate was used as a filter without the need for black infill between filter elements. The screen was either permanently combined with the plate (as it was with Autochrome) or the screen could be separate from the sensitive plate and put in place during the exposure and again when viewing. Separate screen processes had the advantage that the image could be duplicated by contact printing and were processed as ordinary plates, the difficulty lay in producing screens with exactly the same positioning of the filter elements and registration of the taking and viewing screens.

Having a colour screen next to the emulsion was first proposed, as was much else related to colour photography, by Ducos du Hauron in 1868. The first commercially available process was by John Joly where a separate screen of parallel lines was used.⁵

The image on the right shows the colour screen, taken with a microscope magnification of 48x.

Autochrome Images

These quarter-plate images were taken by Herbert Young in the late 1910s.