Autochromes Lumière

 

Potato Starch

The uniqueness of the Autochrome lay in the preparation of the layer composed of dyed granules of potato starch. Some uncertainties remain concerning the nature and the exact time-line of Louis Lumière's early investigations into suitable materials for his invention, in particular between 1900 and 1903, when he deposited the first patent. In the patent, besides the starch, we find the following materials cited: some pulverised enamels, some ferments, some bacillus, as well as all the powdered and transparent material. It seems that the superiority of the starch resided in its capacity to soak up colour, along with the advantage of being practically spherical in shape.

From Conception to Realisation
Four years separated the deposit of the initial patent from the commercialisation of the first Autochrome plates, due to the difficulties of industrial production encountered by the Lumière brothers. In the first place, the "grain" elusively referred to by Ducos-du-Hauron had to be developed and a substance capable of supporting the colours had to be found. They directed their research towards the use of starch. In their investigations, the Lumière brothers took advantage of their many business relations abroad, through ties forged in the distribution of their diverse products, to have samples sent from all over the world.
 
Among the many letters which kept these exchanges going, we find one from the end of 1903, a response from the Lyon municipal laboratory director to Louis Lumière, that reads: "included here is a list of starchy materials I promised you yesterday evening while we were returning to City Hall. Understand that, in leaving the responsibility to the authors who have determined them, I guarantee neither the dimensions nor the given forms for the amylased granules contained..."

This note is followed by a well-documented list of some thirty-eight different kinds of starches. This list included common cereals such as oats, wheat, rye and barley, as well as some other, more rare materials like yam (a tropical plant providing a starchy tuber, different from the sweet potato, which often goes by the same name) or tacca oceanica (a species of tropical herb with an edible tuber). In the end however, the Lumière brothers decided on potato starch. The size of the starch particles contained in the potato could vary between 5 and 100 microns, which was not favourable for the application they envisioned, but this disadvantage was greatly compensated for by the good dying properties. These properties of potato starch allowed for the constitution of a sufficiently selective screen, capable of responding to the spectral specifications of the trichromatic selection.
By the end of 1903, Louis Lumière was investigating French sources of starch, looking to obtain the sort of small granules of starch provided by the potato.