With the last roll of Kodachrome slide film ever to be manufactured by Kodak now developed, a major chapter of the film photography era is winding down. Dwayne's Photo Service of Parsons, Kansas, is the only lab left in the world that still processes this type of film, and it plans to stop processing Kodachrome on December 10. Kodak itself had previously farmed out what remained of its in-house film processing business to Dwayne's in 2006.
Kodachrome wasn't the first color film, but it was the first successful commercial film based on a subtractive process; earlier additive processes used filters, which limited quality. First developed for use as a movie film, the Kodachrome process -- in which three emulsions, each sensitive to a primary color, are coated on a single film base -- was invented by Kodak's Leopold Godowsky Jr. and Leopold Mannes in 1935.
Modern color slide films all use a subtractive process. In this regard, Kodachrome essentially served as a template for all subsequent mass-market color slide films, including Kodak's own Ektachromes.
However, at a more detailed level, Kodachrome isn't much like other slide films. The differences are a big reason why Kodachrome remained popular for so long, in that they improved image longevity and helped photographers produce uniquely colorful images. But they're also the reason that maintaining this line of film became untenable for Kodak as its volumes shrank.
In most slide films, the couplers (color formers) for each subtractive color are added to the appropriate emulsion layers of the film when it is manufactured. Agfa pioneered this approach in 1936.
All dye images (typically three) are then formed simultaneously during the color developer stage of processing. E-6 is the name of the commercial process. While somewhat exacting with respect to time and temperature, running film through E-6 is still relatively straightforward. It's used by commercial labs to develop Ektachrome, Fujichrome, and essentially all other modern slide films; even amateurs can run film through an E-6 process at home.
Not so with Kodachrome.
The film is essentially a multilayer black-and-white film, meaning that the color formers have to be added in a very carefully controlled way during the development process, the current generation of which goes by K-14.
The first developer merely forms three superimposed negative images of the original scene, one in each of the red-, green-, and blue-sensitive emulsion layers. To introduce color, the film needs to be re-exposed to light multiple times through filters of various colors and subsequently developed in appropriate chemicals. These steps essentially colorize the unexposed and undeveloped silver halide in each the three emulsion layers, which is to say the positive image. The silver is then removed, leaving the three positive dye images.
It's a very exacting and complicated process relative to E-6 and has always been handled by a relatively small number of labs. (Prior to a 1954 consent degree, Kodak wouldn't even sell the chemicals needed to do the processing.)
Film sales have dropped significantly. Film isn't going away anytime soon. But lower volumes tend to lead to fewer choices. That Kodachrome is one of those choices being weeded out is certainly nostalgia-provoking. It was a favorite of many professional photographers. I myself liked it and shot many rolls, albeit fewer in recent years after Kodak started to come out with new generations of Ektachrome that I favored for many purposes.
And today, well, it's been well over a year since I've shot a roll of film. But that doesn't mean that I can't fondly remember Kodachrome.