C-41 process
C-41 is a chromogenic
Chromogenic refers to color photographic processes in which a traditional silver image is first formed, and then later replaced with a colored dye image.- Description :...

 color print film
Color print film
Color print film is the most common type of photographic film in consumer use. Print film produces a negative image when it is developed, requiring it to be reversed again when it is printed on to photographic paper....

 developing 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 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 layers

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 the classic illustrative example, there are three emulsions: one is red sensitive, another is green sensitive, and the last is blue-sensitive. The top layer is blue-sensitive. Beneath the blue layer is a yellow filter, composed of dyes or colloidal 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.

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 sensitive to each color. Each of these 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. Some films are top-coated with UV blocking layers or anti-scratch coating
Anti-scratch coating
An anti-scratch or scratch-resistant coating is a film or coating that can be applied to optical surfaces, such as the faces of a lens or photographic film. The coating does not interfere with how the lenses function and does not affect vision, but creates a permanent bond with the lens that...

s. There also may be layers to space different emulsions, or additional filter layers.

C-41 Processing can not be done on TRUE black and white negatives.

Each emulsion layer, in addition to the light-sensitive components, contain chemicals called dye couplers. These couplers, located in the blue, green and red-sensitive layers, produce yellow, magenta and cyan dyes, respectively, when developed.


The C-41 process is the same for all C-41 films, although different manufacturers' processing chemistries vary slightly.

After exposure, the film is developed in a "color developer". The developing ingredient is a paraphenylene diamine
p-Phenylenediamine is an organic compound with the formula C6H42. This derivative of aniline is a colorless solid, but typically samples can contain yellowish impurities arising from oxidation. It is mainly used as a component of engineering polymers and composites. It is also an ingredient in...

-based chemical known as 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 over-development of the film.

After the developer, a bleach removes the metallic silver
Silver is a metallic chemical element with the chemical symbol Ag and atomic number 47. A soft, white, lustrous transition metal, it has the highest electrical conductivity of any element and the highest thermal conductivity of any metal...

 generated by development. After the bleach, a fixer removes the unexposed undeveloped silver halide. This is followed by a wash, and a final stabilizer and rinse to complete the process.

There are simplified versions of the process that use a combined bleach-fix
Ethylenediaminetetraacetic acid, widely abbreviated as EDTA , is a polyamino carboxylic acid and a colourless, water-soluble solid. Its conjugate base is named ethylenediaminetetraacetate. It is widely used to dissolve limescale. Its usefulness arises because of its role as a hexadentate ligand...

 that dissolves the silver
Silver is a metallic chemical element with the chemical symbol Ag and atomic number 47. A soft, white, lustrous transition metal, it has the highest electrical conductivity of any element and the highest thermal conductivity of any metal...

 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

Like the black-and-white film process, the C-41 process can be used to push process
Push processing
Push processing in photography, sometimes called uprating, refers to a film developing technique that increases the effective sensitivity of the film being processed. Push processing involves developing the film for more time, possibly in combination with a higher temperature, than the...

 films. 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.

The negative

The resulting film is a negative, meaning that the darkest spots on the film are those areas that were brightest in the source. Nearly all C-41 films also include an additional orange mask to offset the optical inadequacies of the dyes in the film. 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. The finished negative is printed using color photographic paper
Photographic paper
Photographic paper is paper coated with light-sensitive chemicals, used for making photographic prints.Photographic paper is exposed to light in a controlled manner, either by placing a negative in contact with the paper directly to produce a contact print, by using an enlarger in order to create a...

 to yield a positive image.

Use with black-and-white films

While C-41 is usually considered a color process, Kodak manufactures a C-41 black-and-white
Black-and-white, often abbreviated B/W or B&W, is a term referring to a number of monochrome forms in visual arts.Black-and-white as a description is also something of a misnomer, for in addition to black and white, most of these media included varying shades of gray...

 film called BW400CN. Ilford
Ilford Photo
Ilford Photo is a manufacturer of photographic materials known worldwide for its black-and-white film and papers and chemicals, as well as its range of Ilfochrome and Ilfocolor colour printing materials. Ilfochrome was formerly called Cibachrome, developed in partnership with the Swiss company...

, a British company, produces a similar film known as XP2 Super. Fuji
is a multinational photography and imaging company headquartered in Tokyo, Japan.Fujifilm's principal activities are the development, production, sale and servicing of color photographic film, digital cameras, photofinishing equipment, color paper, photofinishing chemicals, medical imaging...

 produces a third film called Neopan 400CN.

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 the Ilford 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.

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
Technical Pan
Technical Pan was an almost panchromatic black-and-white film produced by Kodak. While it could reproduce the visible light spectrum, it leaned to the red, and so unfiltered outdoor shots would render blues, most notably the sky, with additional darkening and reds with some lightening. These unique...

 film; 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.

Cross processing

It is also possible to cross-process
Cross processing
Cross processing is the procedure of deliberately processing photographic film in a chemical solution intended for a different type of film. The effect was discovered independently by many different photographers often by mistake in the days of C-22 and E-4...

 slide film
Transparency (photography)
In photography, a reversal film is a type of photographic film that produces a positive image on a transparent base. Also known as dias or slide. The film is processed to produce transparencies or diapositives instead of negatives and prints...

 for the E-6 process
E-6 process
The E-6 process is a chromogenic photographic process for developing Ektachrome, Fujichrome and other color reversal photographic film....

in C-41 , which yields negatives with a color shift and stronger saturation. (C-41 also may be processed in E-6 yielding positive images with a strong green cast, caused by the orange mask.) Varying brands and film speeds yield different color shifts producing bright, saturated colors and high contrast.

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.

External links

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