Paget plates were an early colour photographic medium, similar in principle to Autochrome plates. The system was patented in 1912 by G.S. Whitfield, and sold by the Paget Prize Plate Company (which later was one of the companies that merged to form APM. They were renamed 'Duplex' plates from about 1920.. The process was further developed as the Finlay plate in 1929, but chromogenic processes (Kodachrome and Agfacolor) largely replaced such processes within a few years.
Like Autochrome, the Paget plate was a monochrome plate, exposed through a three-colour filter screen. The image produced was essentially three interlaced images taken though different colour filters. The plate (separated from the colour screen) was developed as a negative, from which a positive could be made on a second plate by contact printing. This could then be viewed or projected, again with a colour filter screen to convert the three component monochrome images back to their colours. The three component colour images combined to make a true colour image. This kind of method is known as additive colour synthesis, in contrast to the subtractive method used in later colour-positive processes such as Kodachrome.
In an Autochrome plate, the filter screen is attached permanently to the plate. With the Paget system, however, a separate glass screen is used (it is inserted in front of the plate in the dark slide). This has the advantage that different screens can be used for taking and viewing the photographs. A less strongly coloured filter was used for the 'taking' screen, increasing the effective speed of the plate, at the expense of colour saturation; their slow speed was a major disadvantage of early colour processes. Another advantage of the separate screen is that as many positive plates can be produced from a negative as desired; in addition, the negative plate can be used to make monochrome prints on paper. Finally, the cost of plates suitable for the use with the Paget screen was about one sixth the cost of one with an integral colour screen. However, the distance between the colour screen and the silver image in the finished slide creates a problem: if the slide is not viewed at more or less a right angle, each element of the silver image may align with the wrong element of the colour screen, giving untrue colours.
The pattern of the colour screen also differs from the Autochrome plate, being a regular array of red, blue and green, rather than the Autochrome's random array of coloured dots. The 'viewing' filter screen had to be lined up perfectly with the plate for the colour image to be correct; once aligned, the 'viewing' screen would be fastened to the plate. The 'taking' screen, however, would be reused for every exposure. Special plate holders were available that allowed the screen to be inserted and removed in daylight, so that a dark bag was not needed in the field.
- Short explanation of the Paget plate process for an exhibition at the Australian War Memorial of photographs from the First World War using it, and including photos by Frank Hurley, who was a war photographer in the First and Second World Wars.
- Chronology of colour processes at Autochromes Lumière, a project of the French Ministry of Culture.
- Woodhead, A.E. (1914) 'Photography in colour'; Journal of the Society of Dyers and Colourists Vol. 30, No. 3 (March 1914), pp 78-84.
- The caption to a Paget photograph by Sarah Acland states that the Paget plate was two stops faster than Autochrome; in the exhibition Cameras: the Technology of Photographic Imaging at the Museum of the History of Science, Oxford, 20 May - 13 September 1997.