E-6 process

The E-6 process (often abbreviated to E-6) is a chromogenic photographic process for developing Ektachrome, Fujichrome and other color reversal (also called slide or transparency) photographic film.

Unlike some color reversal processes (such as Kodachrome K-14) that produce positive transparencies, E-6 processing can be performed by individual users with the same equipment that is used for processing black and white negative film or C-41 color negative film. The process is highly sensitive to temperature variations: a heated water bath is mandatory to stabilize the temperature at 100.0 °F (37.8 °C) for the first developer and first wash to maintain process tolerances.

History
The E-6 process superseded Kodak's E-3 and E-4 processes. The E-3 process required fogging with light to accomplish image reversal and produced transparencies that faded quickly. The E-4 process used polluting chemicals, such as the highly toxic reversal agent borane tert-butylamine (TBAB).

Non-Kodak color reversal films introduced in the 1980s were compatible with the E-6 process, including variants of Fujichrome and Agfachrome, sold by Fujifilm and Agfa-Gevaert, respectively; one notable exception was Fujichrome 1600 Professional D, which was compatible with E-6 but used a customized PZ process for best results. The PZ process was similar to E-6, but used a different fog-suppressing chemical.

Process variations
There are two versions of the E-6 process. Commercial laboratories use a six-bath chemical process. The 'hobby' type chemistry kits, such as those produced by Tetenal, use three chemical baths that combine the color developer and fogging bath solutions, and the pre-bleach, bleach and fixer bath solutions.

Six-bath process version
The structure of E-6 film has three separate light-sensitive layers; each layer is sensitive to a different group of wavelengths corresponding to red, green, and blue colors. When the film is exposed, each layer records a latent image based on its sensitivity. A yellow filter prevents blue light from exposing the green- and red-sensitive layers, which have some sensitivity to blue light.

Kodak Publication Z-119 provides instructions for various methods to carry out the E-6 process, including the use of continuous processors, roller-transport processors, rack-and-tank processors, batch processing, and rotary-tube processors; however, they largely share the same steps and recommendations for time and temperature with the exception of rotary-tube processors. The first developer, first wash, and reversal bath must be carried out in darkness.