| Fujichrome Sensia 200 slide film,|
cross processed in C-41 chemistry
image by Pablo Hache (Image rights)
Cross-processing is an experimental technique where films are developed in the "wrong" chemistry for their emulsion type, giving unexpected shifts in color palette or contrast. Users of cross-processing often shorten the term to xpro.
But in the structure of their emulsions, slide and print film are essentially similar. Their manufacturers have simply engineered the color balance and contrast of each to best match the standard processing they'll receive. When a color film is put through the "wrong" chemistry, an image still results, just one that is different from what the manufacturer aimed for.
While cross processing has happened as an occasional lab mistake throughout the history of color film, some more experimentally-minded photographers began seeking it out deliberately for the unusual visual effects produced. More recently, the xpro effect has been widely publicized through the activities of the Lomographic Society and users of its cameras. But it is the processing itself, rather than any particular type of camera, which causes the effects.
There is often some dispute about whether cross-processing damages the chemistry or calibration of automated processors; many labs refuse to cross-process film, believing that it does. When cross-processed film is a small percentage of the total, its effect is likely to be negligible.
The exception is processing movie film or Kodachrome in the wrong processes. These films are coated with a rem-jet antireflection backing, which can float loose and gunk up a processing machine.
Slide film in C-41
This is by far the most popular form of cross processing. It gives punchy, alien colors and sometimes blasted-looking contrasts. In this process, the slide film develops into a negative, although one lacking the typical reddish tint of normal C-41 negatives. Some of the classic "xpro look" may result from automated printing or scanning machines not coping well with the unexpected color balance. When scanning ones own film, the color and contrast are quite manipulable—from nearly normal to extremely wacky.
The heightened contrast accentuates any vignetting produced by a camera's lens—an effect that shows up with many toy cameras, as well as the Lomo LC-A, the Olympus XA2, and the Vivitar Ultra Wide & Slim
| Ferrania Solaris print film,|
cross processed in E-6 chemistry
image by easy.beta (Image rights)
Print film in E-6
Much less commonly seen, this leads to a positive transparency with a muted, pastel contrasts. The color balance tends to shift towards pink or yellow.
Color film in B&W chemistry
This form of cross processing does not activate any of the color dyes in the film, and so results in a monochromatic negative. (Using color-film settings when scanning may yield varying tints across the frame.) Without the use of a color-process bleach step, the negative may have a dense coffee-colored background that is difficult to work with.
Distorted xpro colors have become such a part of today's visual culture that digital simulations of them are ubiquitous. Xpro effects are a standard setting on many new digital cameras. There are also numerous smartphone apps and image-editor plug-ins that serve the same purpose.