So how did it work? Essentially, an Autochrome plate is a thin piece of glass—available sizes ranged from about 6 by 8 inches on down, and the plates could be used in any of a wide variety of cameras—coated with a light-sensitive silver-gelatin emulsion and a thin layer of thousands of potato-starch grains, each dyed one of three colors: green, blue or red. The tiny grains were evenly mixed over the surface and compressed, forming a color screen much like those on a TV tube or a computer monitor—"primitive pixels," in the words of a French customer of Kraus’s. The grains acted as filters, and when light passed through them on its way to the emulsion at the time of exposure, its intensity at each point was modulated by the grains, so that blue grains would transmit more blue light and less red, and so forth. After the emulsion was developed to a negative, it was then chemically reversed into a positive. The image itself was black and white, but the starch-grain filter layer was still intact, so seen through that layer, the image appears in accurate color. When the development was done, a second glass plate was placed over the emulsion and the edges sealed with a special black tape. Since the filter layer is necessary both for taking and for viewing the picture, each Autochrome—unlike, say, a negative from which multiple prints can be made—is a unique object, which naturally increases its appeal to collectors.

As soon as it was introduced, Autochrome "took the world by storm," says Kraus. "Within the first year all the major photographers were using it." Walker Evans famously said, "Color is vulgar," speaking for a large contingent of artistically serious photographers, but there were no such scruples in 1907 as the leaders of the avant-garde Photo-Secession—Alfred Stieglitz, Steichen, Alvin Langdon Coburn—as well as European Pictorialists like Heinrich Kühn, took to it with vigor.

The interest quickly reached the level of a craze. Coburn took moody photographs of the London docks on Autochrome plates, and created a color portrait of Mark Twain reclining, as was his wont, in bed. Steichen’s portraits of Spaulding, who was beautiful as well as talented, clearly show his joy in exploiting the chromatic possibilities of the new invention, and he also turned his lens on flowers, nudes and landscapes.

"Steichen brought the process over to the U.S. the year the Lumière boys brought it out," and he even planned to write an instruction book on it, Bannon explains. Steiglitz held several Autochrome exhibitions at his gallery "291."

But by around 1914, these heavy hitters of American photography had moved on to other things, which makes their Autochromes particularly rare. Why did their enthusiasm wane so quickly? Pamela Roberts, a former curator at the Royal Photographic Society in London and author of the recently published book A Century of Colour Photography thinks this was because Autochromes are difficult to exhibit. "Projected with a back light, it turns into a lecture or audience experience, which is not what the Secessionist people were after. They wanted photography as a fine art," she notes.

They also may have become frustrated with the technical limitations: Autochrome plates required very long exposures that made capturing movement nearly impossible, plus there was little opportunity for tweaking the image’s development in the darkroom. Furthermore, with a black-and-white negative one could make a variety of different kinds of prints, from the regular gelatin-silver to more exotic types like platinum and gum bichromate. (Steichen’s 1904 landscape "The Pond–Moonlight," which sold for a $2.9 million, the record for any photograph, at Sotheby’s New York in February 2006, has been mistakenly described as an Autochrome. The piece is actually a multiple-layer gum bichromate print.)

Despite the defection of some, Autochrome remained immensely popular, especially in its native France, until it was discontinued in 1932. Some of the best practitioners were not self-conscious artists but documentarians and magazine photographers, and as Kraus points out, the vast majority of Autochromes that come on the market were taken by nameless amateurs who shot them on weekends or on their vacations. (They were generally wealthy and technically skilled, since Autochrome plates were expensive and had to be processed by the photographer.) Many had an excellent eye, and their humbly conceived works are now eagerly sought by collectors.

One of the most assiduous of these—and probably the foremost collector of Autochromes in the U.S.—is Madison, Wisconsin–based Mark Jacobs. "We’re a small but intense group," he says.