Autochrome

Manufacturing

A varnish-coated glass plate is covered with a thin, even layer of potato starch grains tinted green, blue-violet and orange, then protected by another layer of varnish onto which a photosensitive gelatine-silver emulsion is applied. The plate can then be exposed in the camera, developed and reversed into a positive image. A final layer of varnish can then be applied. The monochrome positive silver image is then viewed through a coloured filter which, by additive synthesis, gives us a colour image. 

Identification

These different processes are identified by examining under magnification the coloured screen, which may be geometric or random. The pattern of the autochrome image is random and has a pastel, textured appearance, whether on glass or plastic, which is not the case with later chromogenic processes with more saturated, sharper colours.

Deterioration

Autochromes are fragile collation of multiple components (gelatin-silver image, varnish, dyes), all of which are sensitive to the photograph’s deterioration agents: variations in temperature and humidity, pollutants and oxidants, light, etc. Glass breakage, delamination of the image layer from its glass substrate, and fading of the dyes are common forms of deterioration observed on autochrome plates.

Glossary