Let’s be clear, colour in photography was a major preoccupation of photographers and scientists who were interested in that art form and this, since the appearance in 1839 of the daguerreotype. It is even likely that the absence of day colour was detrimental to the spread of this photographic process as the zeitgeist allowed to envisage the wonderful possibility sooner or later of fixing colour. It was enough to wait, or to compensate for this lack by colouring the photographic image with the hand.
Nevertheless, the dependence of colour photography on techniques closely associating physics and chemistry required ample knowledge; a visionary mind and an obstinacy that few scientists could command.
As soon as september 1829, Nicéphore Niepce himself foresaw colour photography. He wrote in a book he planned on heliography (photogravure) « It is the fruit of several years of research on the solution to an equally interesting and curious question that derives from it, the question of finding in the emanation of the light fluid an agent that could imprint in an accurate and lasting manner images transmitted through optical processes; to imprint them, I don’t mean with the brightness and diversity of their colours, but with all the degradations of tints from black to white. I think, in fact, that although it is not impossible to discover, with the help of chemical combinations, a phosphorescent substance that has the singular property of retaining the coloured rays of a prism, it would be pretty difficult to get hold in that manner of an imprint that would not quickly alter ». This thought was the result of the knowledge he had of research work on light which « when it is decomposed by a prism, displays its richest colours » a work carried out by his partner Louis Daguerre. In a letter to his son Isidore dated 2nd and 4th September 1827 « [Daguerre] continues to believe that I am more advanced than he is in the research that concerns us. What is well demonstrated now is that his process and mine are quite different. There is something wonderful about his, and in its effects, a promptness that can be compared to that of electric fluid. Mr. Daguerre has managed to fix on his chemical substance, some of the coloured prism rays. He has already gathered four of them and he is working to gather the other three to obtain the 7 primary colours » He even indicated the chemical component that Daguerre used, a very thin powder reacting in a most analogous way « with barium sulphide or Bologna stone (phosphore), that also has the property of retaining some prism rays ». In a paper submitted to the Academy of Science in 1851, he concluded that metal silver could become coloured thanks to chlorine when it is in the state of chloride or chlorate. He raised, though, the difficulties encountered: the chemical surface that resists maintaining several colours at a time, coloured alterations, and worse than that, « this fixing of basic colours is reduced to fugitive nuances that are so feeble that they cannot be perceived in broad daylight ».
Expectations were so high that a true passion inflamed scientists’ spirits all across the world.
Like Daguerre and Niépce, Levi Hill, an American Baptist minister, met this alteration of colours. In 1850, he nevertheless claimed he had met the challenge of colour fixing through a daguerreotype process « in natural colours ». Quite naturally, he was immediately successful, but very quickly doubts began to arouse then a major controversy emerged on both sides of the Atlantic finally ending up in disgrace. His process named hillotype was based in part on colouring, and Levi Hill did not overcome this fraud. Was it true colour photography – even if it was the result of chance – or daguerreotype painting? The question remains. And since studies and experiments conducted by Joseph Boudreau and Mike Jacob, a definitive study should be made to establish the truth on what remains an enigma  .
A short time before,Edmond Becquerel, cooked chemical products to obtain at last a recipe allowing to get a product likely to conserve the image of the light spectrum. He managed to do that in 1848 on a silver plate lined with a sensitive layer of silver subchloride, a mixture known for a decade by scientists such as Thomas Johann Seebeck, Sir John Herschel or Robert Hunt.
The Scottish physicist James Clerk Maxwell worked on a new theory of colours leading to trichromy (1855), but based on the additive synthesis method that reconstructs a colour thanks to three basic colours (red, green, blue). In 1861 he explained how the principle could be applied to photography at the Royal Institution with his famous photograph of a tricolour ribbon. Strangely enough, this method was a little forgotten before being studied again by Hermann Wilhelm Vogel, a German scientist, who worked to produce emulsions sensitive to primary colours only. Nevertheless, we had to wait until the early XXth century for the emulsions to be precise enough and sensitive enough to be applied to traditional photography.
During the universal exhibition of 1867, the Frenchman, Alphonse Poitevin presented heliochromes of Niépce printed on glossy paper or paper. Improving his process, he filed a patent on 18th December 1865 and entrusted its commercial and industrial exploitation with maison Garin, Guilleminot and Berthaud of Paris.
But colour fixing remained haphazard still, to such an extent that a good many researchers considered questioning this tampering. But light is avaricious, and though it offers colour, it lends it temporarily and takes it back much to man’s despair. And since it proves intractable in its obstinate integrity, man steals its property by violating, decomposing its light in the three prime colours, an « indirect » method !
Two men simultaneously had the idea of this method, Charles Cros and Louis Ducos du Hauron. Unlike Ch. Cros somewhat deprived of tangible proof, Louis Ducos du Hauron took care to demonstrate the veracity of his process by presenting on 7th May 1869 a material proof to the audience of the French Photographic Society; a still-life of natural elements such as tree leaves laid on a transparent surface (probably a pane) photographed by contact in a darkroom, by submitting it to a rather long exposure. This photograph was presented in February 1870 with a handwritten cartel by Ducos du Hauron indicating « Collographic reproduction of leaves and flower after a trio of negatives whose gelatin printing was produced in the form of diaphanie (transparency) in a session of the French Photographic Society (February 1870) ». It is therefore the first true colour photography in the world.
First, Louis Ducos du Hauron used a photographic process he named trichromy based on the decomposition of light in three basic colours by selecting yellow, magenta and cyan. Then he associated these results to recreate a colour image.
Secondly, he developed two photomechanical techniques ; Woodburytype printing, very close to the coal technique, and collotype, that became a major element of colour mass printing.
He described his techniques in various publications in the course of his life between 1869 and 1920 with the help of his brother who supported him morally and financially all through his life.
More about it here
Colour, however, is but a stage for scientists and photographers. Nature is not static, it moves. Nature is not plane. It offers depth. And quite naturally, this raises the question of restoring movement and relief. It is then no wonder that these scientists should look into these questions. Along with research on colour, many of them attempted to produce artefacts that will lead to cinema and relief vision.
Louis Ducos du Hauron was one of them and the fact that he resolved in part the questions of colour, movement and relief gives a particular aura to his genius.
We will see this work on cinema in more detail here
We will see this work on relief photography in more detail here
 Handwritten letter to Isidore Daguerre (Collection of the Nicéphore Niépce Museum of Chalon-sur-Saône.
 See, "Le point de vue français dans l’affaire Hill" by François Brunet in N° 16 of "études photographiques" of May 2005 : Convention « Photography, the issues of history » or online on https://journals.openedition.org/etudesphotographi...
 Charles Cros only presented his first colour photograph in 1876. It is also a still-life (a painting, a glass, a plate), and this handwritten note « first print of my photochromy process. To Victor Meunier, my scientific sponsor). This photograph is part of the collection of the main library of the National Museum of Natural History of Paris.
 Word used by LDH to name a slide
 It is still featured today in the Nicéphore Niepce museum of Chalon-sur-Saône. (MNN 1979.46.8. Format: 22.5 x 16.5 cm.)
 Link to other pages presenting trichromy
 Link to other pages presenting cinema
 Link to other pages presenting 3D