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((Short description|Color film developing process))
((More citations needed|date=September 2018))
'''C-41''' is a [[chromogenic]] [[color print film]] [[photographic processing|developing process]] introduced by [[Kodak]] in 1972,((citation needed|date=September 2018)) superseding the [[C-22 process]]. C-41, also known as CN-16 by Fuji, CNK-4 by Konica, and AP-70 by AGFA, is the most popular film process in use, with most, if not all photofinishing labs devoting at least one machine to this development process.

Processed C-41 negatives, as with all color films, consist of an image formed of dye. Due to the long-term instability of dyes, C-41 negatives can fade or color-shift over time. This was a significant problem with early films; whether the newer films are archival or not is a subject of some debate.

==Film structure==
[[File:Fujicolor superia film structure.svg|alt=Diagram of FujiColor Supreria C-41 film|thumb|upright=2.5|[[Fujifilm Superia|FujiColor Superia]] is an example of a C-41 process film. This diagram illustrates the layers [[FujiFilm]] has chosen for this film.  Note the [[antihalation]] layer.]]
C-41 film consists of an acetate or polyester film base, onto which multiple emulsions are coated. Each layer is only sensitive to a certain color of visible light.

In an idealized, illustrative example, there are three light-sensitive layers: one is red-sensitive, another is green-sensitive, and the top is blue-sensitive. Beneath the blue layer is a yellow filter, composed of dyes or colloidal silver, also known as [[Mathew Carey Lea|Carey Lea Silver]]. All silver-based photographic emulsions have some sensitivity to blue light, regardless of what other colors they may be sensitized for. This filter layer serves to remove the blue light, which would expose the layers beneath it. Beneath the blue-sensitive layer and the yellow filter are the green- and red-sensitive layers.<ref name=Nadler-78/>((rp|2-6))

Each emulsion layer, in addition to the light-sensitive components, contains [[dye coupler]] chemicals. These couplers, located in the blue-, green-, and red-sensitive layers, produce yellow, magenta, and cyan dyes, respectively, when developed.<ref name=Nadler-78/>((rp|2-6))

The illustrative example outlined above differs from the design of actual film, in respect to the number of layers. Almost all C-41 films contain multiple layers for each color-sensitive layer. Individual layers have different speed and contrast characteristics, allowing the film to be correctly exposed over a wider range of lighting conditions.

In addition to multiple emulsion layers, real films have other layers that are not sensitive to light. In some cases, the base is first coated with an [[antihalation]] layer to minimize reflections. Some films are top-coated with UV-blocking layers or [[anti-scratch coating]]s. There also may be layers to separate different emulsions, or additional filter layers.<ref name=Nadler-78>((cite book |url=https://archive.org/details/colorprintingman0000nadl/ |title=The Color Printing Manual |first=Bob |last=Nadler |date=1978 |publisher=Amphoto (American Photographic Book Publishing Co., Inc.) |location=Garden City, New York |isbn=0-8174-2414-8 |url-access=registration))</ref>((rp|2-5))

===The negative===
[[File:35 mm Kodak film negative held between fingers.jpeg|thumb|right|upright|[[Kodacolor (still photography)|Kodacolor Gold]] 100 film, exposed and developed negative, showing characteristic orange base color and inverted colors]]
After processing, the resulting film is a negative, meaning that the darkest spots on the film are those areas that were brightest in the source. Light is projected through the finished negative onto color [[photographic paper]], yielding positive image prints.

Nearly all C-41 films also include an orange mask to offset the optical inadequacies of the dyes in the film.<ref name=Watkins-78>((cite book |url=https://archive.org/details/focalguidetocolo0000watk/ |title=The FOCALGUIDE to Colour Film Processing |first=Derek |last=Watkins |date=1978 |publisher=The Focal Press |location=London |isbn=0-240-50994-3 |url-access=registration))</ref>((rp|27)) These C-41 negatives appear orange when viewed directly, though the orange base is compensated for in the formulation of color print materials. Some C-41 films, intended for scanning, do not have this orange base.

==Process==
{|class="wikitable" style="font-size:100%;text-align:left;"
|+Color negative film exposure and procesing schematic<ref name=Watkins-78/>((rp|82;117))
! Step !! Name !! Time (mm:ss) !! Temp. !! Illustration !! Description
|-
! 1 !! Loading film
| colspan=2 ((N/A)) || [[File:E-6 step 00.svg|frameless|upright=1]]
| Unexposed film, with light-sensitive grains in three different layers
|-
! 2 !! Exposure
| colspan=2 ((N/A)) || [[File:C-41 step 01.svg|frameless|upright=1]]
| Exposing film, showing different components of light penetrating to the respective light-sensitive layers and resulting selective sensitization of grains
|-
! 3 !! Developer
| 3:15 || ((cvt|37.8|±|0.15|C)) || [[File:C-41 step 03.svg|frameless|upright=1]]
| Sensitized grains are developed and dye coupler clouds are formed
|-
! 4 !! Bleach
| 6:30 || ((cvt|24|–|41|C)) || rowspan=5 | [[File:C-41 step 04.svg|frameless|upright=1]]
| rowspan=5 | Silver is washed out of film, including yellow filter layer, leaving negative with reversed colors
|-
! 5 !! Wash
| 3:15 || ((cvt|37.8|±|3.0|C))
|-
! 6 !! Fixer
| 6:30 || ((cvt|24|–|41|C))
|-
! 7 !! Second wash
| 3:15 || ((cvt|37.8|±|3.0|C))
|-
! 8 !! Stabilizer
| 1:30 || ((cvt|24|–|41|C))
|-
! 9 !! Dry
| 10–20 || ((cvt|24|–|41|C)) || ((N/A))
| Stabilizer contains a wetting agent to enhance spot-free drying
|}
The C-41 process is the same for all C-41 films, although different manufacturers' processing chemistries vary slightly. C-41 was introduced with [[Kodacolor (still photography)|Kodacolor II]] and its professional equivalent, Vericolor II, as the 'Flexicolor' process, replacing C-22, which was used with Kodacolor-X and Ektacolor Professional. Compared to C-22, the working temperature of C-41 is higher, at ((cvt|100|F)), versus ((cvt|75|F)) for C-22; total processing time was cut almost in half with C-41, but it is very sensitive to development bath time.<ref name=Watkins-78/>((rp|112–113))

After exposure, the film is developed in a "color developer". The developing ingredient is a [[p-Phenylenediamine|paraphenylene diamine]]-based chemical branded as [[Color Developing Agent 4|CD-4]]. The developer develops the silver in the emulsion layers. As the silver is developing, oxidized developer reacts with the dye couplers, resulting in formation of dyes.

The control of temperature and agitation of the film in the developer is critical in obtaining consistent, accurate results. Incorrect temperature can result in severe color shifts or significant under- or overdevelopment of the film.

After the developer, a bleach converts the metallic [[silver]] generated by development to silver halide, which is soluble in fixer. After the bleach, a fixer removes the silver halide. This is followed by a wash, and a final stabilizer and rinse to complete the process.

The bleach in C-41 does not use [[ferricyanide]], which increases cost; it is possible to develop C-41 using substitute chemicals, which requires an extra step for a stop bath after the developer.<ref name=Watkins-78/>((rp|194–196)) There are simplified versions of the process that use a combined bleach-fix ([[ethylenediaminetetraacetic acid|EDTA]]) that dissolves the [[silver]] generated by development and removes undeveloped silver halide. These are not used by commercial C-41 processors, and are marketed for home or field use.

===Push processing===
Similar to black-and-white film processing, the C-41 process can be adjusted to [[push processing|push-process]] films. Kodak recommends an additional duration of 30&nbsp;seconds in the developer bath to push certain films by one stop.<ref>((cite web |url=https://imaging.kodakalaris.com/sites/default/files/wysiwyg/pro/chemistry/z131.pdf |title=Kodak Flexicolor Chemicals |date= |publisher=Kodak Alaris |access-date=23 January 2024))</ref>((rp|2-9))

Due to the complexity of the film and exacting nature of the process, the results vary widely; as with black-and-white negatives, the process generally results in a negative that is higher in contrast and sometimes higher in grain.((Citation needed|date=July 2008))

===Cross processing===
It is also possible to [[cross processing|cross-process]] [[reversal film|slide film]] for the [[E-6 process]] in C-41, which yields negatives with a color shift and stronger saturation. Varying brands and film speeds yield different color shifts producing bright, saturated colors and high contrast. C-41 film also may be processed in E-6, yielding positive images with a strong green cast, caused by the orange mask.

C-41 film can be processed in standard black-and-white chemicals, to produce a monochrome negative image. The negatives will typically be of very low contrast, and cloudy, partly caused by the orange mask.

==Black-and-white use==

===C-41 "chromogenic" black-and-white films===
While C-41 is usually considered a color process, [[Ilford Photo|Ilford]] currently manufactures a "[[chromogenic]]" C-41 compatible [[black-and-white]] film, [[XP2|XP2 Super]].<ref name=ap/> [[Kodak]] used to manufacture a similar film, BW400CN, but this was discontinued in August 2014.<ref name=pb/> (These should not be confused with regular black-and-white films, which are not compatible with C-41 chemistry.)

These films work like any other C-41 film; development causes dyes to form in the emulsion. Their structure, however, is different. Although they may have multiple layers, all are sensitive to all colors of light, and are designed to produce a black dye. The result is a black-and white image.

The Kodak film has the same orange base as color C-41 films; the base on XP2 is Purple and Fuji films are clear. The orange base on the Kodak film allows them to be printed with correct blacks on standard color printing machines, but this film can be difficult to print on multigrade black-and-white paper, whose contrast is determined by the use of a colored filter during the printing process. Conversely, the clear-based Ilford and Fuji films sometimes results in off-color prints on color paper, but can be optically printed on black-and-white paper, just like any other black-and-white film.

It is often said that prints from these films do not have grain. While they may not appear to have grain, this statement is technically incorrect. On an image from regular black-and-white film, the individual silver particles forming the image are seen as grain. The image on the C-41 films, however, does not contain silver. Instead, C-41 negatives and prints have clouds of dye, causing the resulting image to appear different from that of silver grain.

===Traditional black-and-white films ((anchor|tradbw))===
While regular black-and-white films are not intended for use with C-41 chemistry, some photographers have used C-41 developer to develop high-contrast black-and-white films (such as traffic surveillance film and Kodak's [[Technical Pan]]). This is done in order to lower the contrast. In this application, only a silver image is formed; the bleach step of the C-41 process is not used, as it would destroy the image.

==See also==
*[[Chromogenic]]
*[[Replenishment (photography)]]

==References==
((reflist|refs=
<ref name=ap>((cite web
|title= Essential Guide to Shooting Film
|date= April 20, 2015
|website= [[Amateur Photographer]]
|url= https://www.amateurphotographer.co.uk/technique/expert_advice/essential-guide-to-shooting-film-46405
|access-date= April 29, 2019))</ref>
<ref name=pb>((cite web
|first= Eric
|last= Reagan
|title= Kodak Professional BW400CN Film is Discontinued
|date= August 21, 2014
|website= Photography Bay
|url= https://www.photographybay.com/2014/08/21/kodak-professional-bw400cn-film-is-discontinued/
|access-date= April 29, 2019))</ref>
))

==External links==
*Kodak [https://imaging.kodakalaris.com/sites/uat/files/wysiwyg/pro/chemistry/z131.pdf process C-41 (color negative) processing manual Z-131] ([[PDF]])

((Photography))

[[Category:Photographic film processes]]

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