Colour at home: C-41, E-6, ECN-2 and what the orange mask is for

Colour film is black and white film with ambitions. The silver still records the light; then couplers in each layer form cyan, magenta and yellow dyes in proportion to the silver developed; a bleach turns that silver back into halide and a fixer removes it, so only the dyes remain. Kits that combine the two steps call the bath a bleach-fix, or blix. The three processes you will meet differ in what they are for, not in that basic idea: C-41 gives a colour negative, E-6 a positive transparency, and ECN-2 a cinema negative with a carbon backing. All three can be done at home. All three care about temperature more than anything else you will do in a darkroom.

Temperature is the game

Tetenal's instructions for the Colortec C-41 kit give the standard rotary process at 38 °C: colour developer for 3 minutes 15 seconds at 100 ±1 °F for one to four films, then the bleach-fix for 4 minutes at 100 ±3 °F, a 3-minute rinse and a 1-minute stabiliser ¹. The developer's tolerance, one degree Fahrenheit, about half a degree Celsius, is the number that matters. A sous-vide circulator in a tub holds it; a bucket and a kettle usually do not. Tetenal's sheet also offers an alternative at 30 °C: developer 8 minutes, bleach-fix 6, rinse 6, and it says to use it when the standard 38 °C process gives uneven results ¹; a hand-inverted tank that cools between inversions is the usual reason.

Notice the batch logic. Tetenal's developer times lengthen with each group of films put through the kit, 3:15 then 3:30, 3:45 and 4:00, and the bleach-fix times lengthen faster, 4, 6, 10 and 15 minutes ¹, because the solutions exhaust, and the sheet says the maximum yield is only reached by processing at least four films at a time ¹. Save up rolls and run them together.

C-41 step by step

Load in the dark as for black and white. Bring the tank and the bottles to temperature in the bath. Developer in, timer on, agitate as the kit's sheet says. Tetenal counts the pouring-out inside each step's time ², and Fotofilmfabriek's sheet counts a 10-second drain the same way ⁶, so start pouring out before the timer ends. Bleach-fix in; it is less fussy about temperature and the time is forgiving, so do not shortchange it. Rinse, in running water or by changing the water every 30 seconds as Tetenal suggests ¹, then the stabiliser, which the film needs and must not be washed off afterwards. Hang to dry. Some kits, such as Fotofilmfabriek's, split the bleach and fixer into separate baths, with an optional warm-up and bleach, fixer and final rinse tolerating 24 to 38 °C ⁶; the ordering is the same.

E-6: slides in three baths

Transparencies need a first developer, which makes a black and white negative, a reversal step, a colour developer, which forms dyes where the first developer did not, and a bleach-fix. Tetenal's three-bath kit folds the reversal into the colour developer. Its table: pre-warm the tank 2 minutes at 38 ±0.5 °C; first developer 6 minutes 15 seconds at 38 ±0.3 °C for one film, 6:30 or 6:45 for larger batches; wash 2:30 at 38 ±0.5 °C; colour developer 6, 7 or 8 minutes at 38 ±0.3 °C; wash 2:30 at 33 to 39 °C; bleach-fix 6, 7 or 8 minutes at 33 to 39 °C; wash 4 minutes; stabiliser 1 minute at 20 to 39 °C; then dry ². Tetenal's times run from the bath's first contact with the film to the next bath's first contact, so pouring out belongs inside the step ². The first developer sets the contrast and the density of the slide, which is why its tolerance is three tenths of a degree and why Tetenal's push is done there: two stops underexposed means 5 minutes 30 seconds more in the first developer ². Tetenal also warns, in capitals, never to leave the first and colour developers open next to each other, and that some plastics absorb colour developer permanently ². Keep a jug for each.

ECN-2 and the remjet

Kodak's Vision3 500T is a motion picture stock. Kodak's brochure lists it as an ECN-2 film, rated EI 500 under 3200 K tungsten light and 320 in daylight behind a Wratten 85 filter, to be handled in total darkness with no safelight ³. On its back is remjet, which Dmitri at Analog Cafe describes as a black carbon layer there to prevent halation and reduce friction in a movie camera ⁴. Put that film through a lab's C-41 machine and the remjet comes off in the chemistry and can foul the machine and other people's rolls, which is why labs refuse it. CineStill 800T is, in Dmitri's words, Vision3 500T "with its remjet layer removed", sold for C-41, and the red halo around bright lights is the missing backing; he says it cannot be prevented, only reduced, and advises metering at 800 ⁴. Home ECN-2 kits exist; their instructions, not this page, cover removing the remjet before development. The reward is a cinema negative with Kodak's own curve, whose stated stops add up to at least eleven ³.

The orange mask

A colour negative is orange because of masking: in the textbook account, the couplers for the magenta and cyan layers are themselves coloured before development, so that the imperfections of the dyes they form are cancelled when the negative is printed. The mask is not a cast to be removed by eye; it is a built-in correction, and scanning software compensates for it when it converts the negative. Which is why a raw camera scan of a negative looks hopeless until the software has done its work; see the scanning guide.

Light and filters

Colour film is balanced for a light. Portra 400 is a daylight film; Kodak's table gives it ISO 100 under 3200 K tungsten with a Wratten 80A, or ISO 125 under 3400 K photolamps with an 80B ⁵. Vision3 500T is the reverse, tungsten-balanced and filtered for daylight ³. Shoot either under the wrong light without the filter and you will be correcting a cast afterwards, which a negative scan tolerates well; a slide shows the cast every time it is projected.

Safety

Colour developers are skin sensitisers; the kit's safety data sheet names the developing agent and the precautions, and nitrile gloves, splash goggles and ventilation are the minimum. Keep bleach-fix away from acids. Keep the baths in the order the sheet gives, label every bottle, return working solutions only to their own working bottles, never to a concentrate, and keep spent fixer and bleach-fix for collection under local rules; they carry silver.