The Joly colour process is an early additive colour photography process devised by Dublin physicist John Joly in 1894.
Based on a method proposed in 1869 by Louis Ducos du Hauron in Les Couleurs en Photographie – Solution du Probleme, the Joly colour process used a glass photographic plate with fine vertical red, green and blue lines less than 0.1 mm wide printed on them.
The plate acted as a series of very fine filters, in a similar way to the later Paget process.
The Joly process was introduced commercially in 1895 and remained on the market for a few years.
[1] A large collection of colour slides by John Joly, mainly of botanical subjects, are held by the National Library of Ireland.