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Autochrome photography flourished from 1907 to the 1930's. Each autochrome is a unique transparency image; there is no negative. Autochrome plates were created by coating a sheet of glass with microscopic starch grains dyed red, green, and blue. These formed a screen of color particles. Carbon black was applied over the plate, filling in the spaces around the starch grains. Then a silver gelatin emulsion was applied over the color screen. When the plate was exposed, the base side was turned toward the subject being photographed, and the color screen acted as a filter over the emulsion. The developed plate rendered a positive color image with delicate color qualities. Often, etched or "frosted" glass plates were used as covers. The frosted glass increases the soft focus quality of the color starch grains which form the autochrome image. This autochrome shows an actor in the 1913 play Sanctuary: A Bird Masque. |
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A common way of viewing autochromes was to use a diascope. A frame at the top holds the autochrome plate allowing light from above to pass through the plate and strikes a mirror inside the device. The mirror is shielded from ambient light by cloth side panels. The viewer looks into the diascope and sees the reflection of the illuminated autochrome. In 1968, this diascope was given to the Library by the family of poet Edna St. Vincent Millay, the subject of one of Genthe's autochromes. |
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Both the glass base and the process used to create these autochromes are subject to deterioration. Glass is easily broken, and dyes are subject to color shifts. Autochromes without protective cover glass easily sustain physical damage. Scratched and peeling emulsion layers and faded colors are common. To protect the emulsion, plates were often varnished and a protective cover glass applied and secured with tape. Both the cover glass and the emulsion plates of this unidentified autochrome are broken. |
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Humidity is particularly damaging to the color dyes on autochrome plates, as seen in this extremely faded autochrome of flowers. If properly affixed, the tape that binds the cover glass to the emulsion plate will seal out humidity. But broken tape seals or fractured glass plates may permit moisture and pollutants to reach and destroy the emulsion. As part of the project to preserve Genthe's deteriorating negatives, many of the Library's autochromes received conservation treatment prior to copying. Treatment included retaping seals, reattachment of peeling emulsion, and replacement of broken glass cover sheets. |
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When this unidentified autochrome portrait was broken, the emulsion layer was torn and lifted from the surface of the plate. The emulsion was reattached during conservation, but it was no longer aligned with the original screen of color starch grains. As a result, the central section of the portrait is black-and-white and the intact outer section is color. |
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Types of autochrome deterioration can be detected by comparing these four examples. |
Library of Congress