This from embleton, whose posts from London are always extraordinary, quirky and uniquely oneirical:
Lumiere Brothers Autochrome Glass Plate c. 1907
Taken by my great-grandfather.
The autochrome plates were the invention of Auguste and Louis Lumiere, who patented the process in 1904 and began to market it commercially in 1907. The process provided the first widely available form of colour photography.
Microscopic grains of potato starch were dyed red, green, and blue-violet, then mixed evenly and coated onto a sheet of glass. A black-and-white emulsion was then flowed over this layer. During exposure, the grains of potato starch on each plate acted as millions of tiny filters. The light-sensitive emulsion was then reversal processed into a positive transparency.
When viewed, light passes through the emulsion and is filtered to the proper color by the starch grains. The resulting mosaic of glowing dots on glass gives autochromes the look of pointillist paintings.
The plates came in a range of sizes. These are 16.5cm by 12cm so sadly get cropped by my scanner.