Back in the 70's I worked with(employed as a consultant) someone who had family connections with the Autochrome process, his mother was French and her family had owned the Lumière company, before it was bought by I think Tellko AG, later to become part of Ciba Geigy, and later an Ilford plant. Technically it still exists as the sales arem of Ilford in France..

Tim had quite a lot of reference materials I'll try and contact him when I'm next in the UK and see what he has.

The secret of the process is the pressure used to squash and compact the starch grains, Autochrome plates and also films where still being made in 1939, I'm not sure when they stopped.