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 History The E-6 process superseded Kodak's E-3 and E-4 processes.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). 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 steps for developing color transparency films using process E6 are: First developer bath: 6:00 @. This uses a potassium hydroquinone phenidone black & white film developer, with the preferred form of phenidone being 4-hydroxymethyl-4-methyl-1-phenyl-3-pyrazolidinone (13047-13-7). The first developer forms a negative silver image in each layer of the film. The first developer is time and temperature sensitive because it controls contrast. First wash: Water stop bath, 2:00 @. This step once used an acetic acid stop bath, but was replaced with a water-only bath for process economy, with concomitant slight reduction of first developer strength. Reversal bath: 2:00 @. This bath prepares the film for the color developer step. A chemical reversal agent is absorbed into the emulsion, which is instantly effective. The reversal step can also be carried out using 800 footcandle-seconds (8.6 klx·s) of this variation is used by process engineers to troubleshoot reversal bath chemistry problems such as contamination and issues of low tank turnover as process volumes decline. Color developer bath: 6:00 @. This step is carried out to completion. The developer contains CD-3 developing agent, and acts upon the chemically exposed silver halide that was not developed in the first developer to form a positive silver image. The