Dyeing the Starch

Dyeing constitutes an important step in the manufacturing of Autochromes. The very remarkable effects of the Autochrome images are explained, partially by the properties of the chosen colouring agents.

A Wide Range of Dyes
Between 1860 and 1900, new types of chemical colouring agents, known by the generic name of aniline aniline
Also known as phenylamine and aminobenzene, analine is an aromatic organic compound that served to manufacture the first synthetic colourants
colourants, were being synthesised by the industry. Although these agents allowed for the creation of a wide range of dyes, they were unsuitable for colour photography, as they were frequently destabilised under the influence of light. The development of satisfactory dyes would not have posed a particular problem for the Lumière's however; they had recruited Alphonse Seyewetz, a chemist who had written his degree on the nature of dyestuffs and was the co-author of a reference work on synthetic colouring agents, as head of the chemical department at the Lumière factories. And so, in a manuscript dated from the first years of production (1908), we find the following colourants referred to: crystal violet, tartrazine, erythrosine J (BASF), patent blue (Meister Lucius) and new crystal solid green 3B (Basel Society for Chemical Industry). And in 1914, the Titres et travaux of Louis Lumière shows that the colourants being used were of the Triphenylmethane Triphenylmethane
A chemical compound whose structure includes three aromatic fixed cycles on the same carbon atom. This structure was found in a number of artificial, synthetic dyes throughout the second half of the 19th century.

Towards the end of the 1930's, Seyewetz wrote, "[The starch granules] are dyed with some basic colourants that provide a high degree of clarity. In particular, to obtain the dyes of orange, green, and violet, we can use mixtures composed of eyrthrosine, tartrazine and indigo carmine, which are quite stable in the light, thanks to a protective varnish that we cover them with to isolate them from the sensitive emulsion and from contact with the air." In the manufacturing notes, dating from 1929, we find most of these same dyes, although the suppliers have changed: patented extra-fine indigo carmine (from the Aktiengesellschaft), pure erythrosine L (Durand Huguenin of Huningue), rose bengal (Société chimique de Bâle-Geigy et Cie), crystal violet (Société des produits chimiques de Saint Denis), new crystallised solid green 3B (Société chimique de Bâle-Geigy et Cie) conserved by the Institut Lumière, contains the following handwritten note: "Basic colouring agents used: bright and tartrazine. A book once belonging to Louis Lumière (Sisley's Unification des noms des colorants les plus phosphine 2J, basic flavin T, rhodamine B, rhodamine 6J, crystal violet, thionin blue G, bright green."

To verify this information, a dozen plates (of indeterminate age) and some coloured starch samples were analysed and the presence of the following colourants were confirmed: rose bengal, erythrosine, patent blue, crystal violet, and new solid green 3B. Meta-coloured malachite green and diiodo flourescein were also present. These last two were certainly a result of the impurities of the new solid green 3B and the erythrosine.

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