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Home » About » Blog » Potato Power: The Magic of Autochromes

One of the most rewarding aspects of working at a place like the Clements Library is that you never know what you might stumble across on any given day. For instance, last summer I noticed a box out of the corner of my eye with the word “Autochromes” scribbled in pencil on the side. I had coincidentally been reading about autochromes a few days prior, so naturally I took this as a sign that I should take a quick plunge down this particular rabbit hole.

The autochrome is considered the first commercially viable format of color photography. Patented by French brothers August and Louis Lumière in 1903, the Autochrome Lumière process afforded photographers around the world a blueprint with which to produce lasting full color images in an economically sustainable fashion.

The secret behind this remarkable technological breakthrough?

Potatoes. Lots and lots of potatoes.

Emulsion and starch-bearing side of an autochrome glass plate.

Blank side of an autochrome glass plate.

Autochrome production hinged upon making batches of finely ground potato starch dyed red-orange, blue-violet, and green. Equal proportions of the dyed starches were blended together and thinly applied to one side of a glass plate, with a light-sensitive silver halide emulsion layer then being added on top of the starch layer. Next, the plate would be loaded into a camera with the blank side facing toward the lens. This guaranteed that upon exposure, light would first have to pass through the blank side of the plate and slowly filter through the colored starch “mosaic” in order to reach the photosensitive emulsion. The resulting lightness/darkness values captured in the emulsion would then be precisely influenced and aligned with the chromatic features inherent in the starch layer. After an image was finalized by chemically processing it into a positive transparency on the same plate, autochromes could then be viewed while backlit so that light passing through the side of the plate with the emulsion layer would in turn dictate how the colored starch molecules were illuminated.

When engaging with an autochrome, our eyes end up blending the millions of little dots of primary colors found in the starch layer in a manner that replicates the full spectrum of real-life color values found in the original scene being depicted. The theory behind this phenomenon is known as “additive color.” This is also how the human eye itself operates, as color-sensitive cone cells in our retinas only respond to either blue, green, or red wavelengths of visible light respectively. Only through the visual processing that takes place in our brains are these three color channels integrated and synthesized into full color.

Photograph of an autochrome as seen through a pocket microscope revealing the vibrancy of the dyed potato starch.

Inside of the “Autochromes” box there were three excellent specimens, all of which were produced by American photographers. All three images are housed in special cases called diascopes that were designed to provide extra protection for the fragile glass plates, guard against overexposure to damaging light (autochromes are particularly prone to fading), and also serve as optimal viewing devices. Diascopes were typically made to open vertically, with an autochrome positioned in the upper half of the case opposite a reflective mirror installed in the lower half. With the emulsion/dyed starch-bearing side of the plate facing outwards away from the mirror, overhead light can pass through a window in the upper half of the case, travel through the emulsion layer, illuminate the starch layer, and ultimately yield a viewable reflection in the mirror below.

Of these three autochromes, one in particular stood out: a portrait of a middle-aged woman attributed to “H. M. Murdoch FRPS.” This image is likely a self portrait of an American photographer named Helen Messinger Murdoch. Born in Boston in 1862, Murdoch initially became a portrait photographer in the 1890s before learning about the Autochrome Lumière process in 1907. After becoming a fellow of the Royal Photographic Society of Great Britain in 1912, she established her reputation as a skilled travel photographer by becoming the first woman photographer to travel around the world. During her travels she produced numerous autochrome plates documenting the people and scenes she had encountered along various stops in the Middle East, East Asia, Southeast Asia, India, the Philippines, Hawaii, and elsewhere. Other autochromes held by the Clements Library include a portrait of an unidentified white woman taken by Arnold Genthe, a portrait of an unidentified white man taken by Julius Caesar Strauss, and a group of eleven assorted autochrome plates (two of which were recently discovered in a separate box of glass slides) that mainly consist of portraits, outdoor scenery, and interior views.

Autochrome self portrait by Helen Messinger Murdoch, ca. 1912. This particular diascope model is a “No. 4 1/2 Diascope” patented by L. A. Dubernet on Sept. 1, 1908.

The Clements Library contains a multitude of vibrantly colorful visual materials including hand-colored photographs, paintings, watercolors, drawings, engravings, maps, lithographs, magic lantern slides, book illustrations, and more. However, these autochromes stand out as the library’s only examples of close representations of natural color. An astounding mix of artistic nous and scientific ingenuity that ushered in the era of color photography, autochromes also remain breath-takingly beautiful objects to behold. Delving into the ins and outs of autochromes was a delightful experience, and I eagerly await the next opportunity to unexpectedly happen upon something extraordinary here at the Clements.

Autochrome plate containing image of an individual dressed as an “Indian maiden on horseback.” Notice how if you examine this picture closely, you can see the tri-color dots of potato starch.