Autochromes Lumière


The Emulsion

Spreading the Panchromatic Photographic Emulsion
The final layer applied to the plate was made up of a very fine panchromatic panchromatic
Sensible to all the wavelengths of the visible spectrum, from violet to red.
photographic emulsion. The thickness of the emulsion layer had, so Louis Lumière tells us, to be just 4 microns thick. The size of the silver bromide crystals used had to be smaller than those of the starch granules, about 0.6 microns. This was a remarkable feat for the time.
One is tempted to believe that it was at this stage that the system would have posed the least number of problems for the Lumières. They had already acquired extensive experience in the preparation of glass-plate negatives, even if chromatic photosensitivity was still in its youth at the start of the 20th century. The three sensitising colourants were: orthochrome T (sensitive to green), erythrosine (sensitive to yellow) and ethyl violet (sensitive to red-orange).
Afterwards, the emulsion was overly sensitive to blue and ultraviolet radiation. To avoid having blue  hue on the photograph, it was therefore necessary to place a yellow filter over the lens of the camera when taking the picture.

Once the emulsion was dry, the plate was cut into several standardised formats, from 8.5x10cm (the smallest) to 18x30cm (the largest). The largest plates were always limited to 18cm. Each plate, on the emulsion side, was protected by cardboard with a face of black paper. The plates were then packed together two by two, and then four packs to a box.