Purple Green Orange Filter Transparent Trichromatic formed of potato starch
The Photosensitive Layer Black and white
 coloured luminous Rays sent by the subject  
 
Direction of Reading and projection
Plates Glass Support
Impermeable Varnish
 
Direction of Exposure
 Coloured Luminous Rays sent by the subject  
   Development 1           Development 2
          negative                   positive        
                        
                         Inversion
 
 
© A. Scheibli
The Autochrome plate uses the principle of the Additive synthesis of the colors, the mixture of the lights orange green and violet forms the white.
The Autochrome plate makes it possible to obtain the image color directly.
It is manufactured as follows, potato starch is used at a rate of 8 to 9.000 grains with mm2.
After having selected the potato flour grains of approximately 7µ, they are divided into 3 batches, each batch is respectively coloured into Orange, in Green and Purple. The 3 batches are mixed to obtain a dye without dominant color.
This mixture is spread out uniformly, without superposition of the grains, on a glass plate covered beforehand with a sticky coating
 then the interstices are sealed by coal dust.
The mosaic trichromatic obtained is rolled with more than 5 tons to cm2 to decrease its thickness
the goal being to improve its transparency thus increasing the sensitivity of the plate and the definition of the image.
The plate is ready to receive an impermeable Panchromatic silver bromide varnish.
The exposure is made with the support plates glass facing the objective.
After the exposure, the development then the inversion of the black layer and white are done without modifying  the trichromatic mosaic.
Visible Image by transparency of
the photosensitive layer