Autochromes Lumière
The technological process > The Manufacturing > The Second Varnish

The Second Varnish

Spreading the Sealing Varnish
The plate had to then be coated by a seal in order to protect the starch granules from the emulsion and processing solutions. This varnish also stopped the colouring agents from bleeding. It was produced with a refraction index close to that of the starch, so it was able to mask many of the small imperfections of the system as well as increase its overall transparency. The varnish solvent should not interfere with the colouring agents or the first varnish, so Louis Lumière came up with a suitable solution of dammar resin from cellulose nitrate plasticized with castor oil in ethyl acetate.

Dammar Gum: 28.8g
Cellulose Nitrate: 7.2g
Castor Oil: 4.536g
Ethyl Acetate: 360ml

The density of this varnish had to be between 0.918 and 0.922.
After the coating, the plates were stored for at least 24 hours before coating the emulsion layer.