Black and white film , also written black and white film , refers to a film material that is used for black and white photography and for films. Although color photography prevailed in the 1970s, black and white photography is still used in special niches. In the film industry , too, with a few exceptions, the classic black and white film has been displaced.
As film material there is a black and white film for photographing of images from a photosensitive layer ( photosensitive emulsion ) of silver halide in gelatine , is applied to a carrier material. The black and white film in the classic sense (this does not mean a chromogenic film) contains microfine silver in the finished image (usually as a negative). So the result is an image made up of different shades of gray. The material is available for small format cameras and normal format cameras ( black and white photography ) but also for film cameras . One speaks of a cinema film .
Black and white films are in many cases not black and white, but colored in different ways. On the one hand, the carrier material or the gelatin layer can have a basic color, and on the other hand, a change in color of the silver image can occur as a result of post-treatment or the type of development. For example, underexposed films treated with copper enhancer turn reddish brown in color.
Black and white film generally consists of three layers:
- Light-sensitive layer, consisting of a retouchable gelatine protective layer and a photo emulsion of light-sensitive silver halides and gelatine, which is spread extremely thinly on the substrate. The emulsion represents the light-sensitive layer,
- Layer support, consisting of plastic, also called film base. At the beginning of the film production the carrier material consisted of very flammable nitrocellulose as well
- Antihalation layer; this is a colored gelatine backing layer (for roll and flat films), 35mm films, on the other hand, do not have a special protective layer, but a colored layer base that reduces exposure to radiation.
Developing a film means making visible the latent image which is present in the light-sensitive photo emulsion of the film as a result of the exposure that has taken place. In general, development means the chemical development of the development nuclei formed. This effect amplifies the latent image by a factor of around 100 million. Only then has photography with short exposure times become possible. The developer himself is a combination of different components in a precisely coordinated relationship with one another that have different tasks and functions. A distinction is made between the actual
Developer substance ( reducing agent )
This reduces the silver ions in the exposed crystals to silver atoms, resulting in a visible blackening.
- Used reducing chemicals
- Hydroquinone , Metol , ascorbic acid , catechol , glycine , para-phenylenediamine , Paraminophenol , Amidol and other
- In the development process, roughly speaking, silver ions are reduced to silver atoms. This process takes place at preferred locations in the crystal, the development nuclei formed during exposure. Thus, in the course of film development, small silver grain agglomerates are created, which are ultimately visible under the microscope. Their different densities within the light-sensitive layer lead to the visually perceived gray tones. The developer itself is oxidized during this process.
Triggering or accelerating substance (developer alkali)
The alkali neutralizes the protons released during development . Every developing substance only works from a certain pH value . The choice of alkali therefore depends on the developing substance. The stronger the alkali, the faster, stronger, but also coarser-grained the developer works.
- Basic chemicals used
The alkali creates an excess of hydroxide ions ( ) in the solution . These neutralize the protons ( ) resulting from the oxidation of the developer .
Protective substance or preservative
The protective substance is intended to prevent the developer from auto-oxidation with the oxygen; without the protective substance the developer would quickly become unusable.
- Stabilizing chemicals used
- Sodium sulfite ( ), potassium disulfite ( )
- In solution, sodium sulphite can easily oxidize with the dissolved oxygen to form sodium sulphate, but the developer substances do this much faster! The protective effect of the sulfite is based on the formation of stable sulfonic acids with the developer substances, so that they cannot be further oxidized by the oxygen.
Retarding or anti-fogging substance (clear holder)
Without means of delay, the development process would proceed too quickly and unregulated. The anti-fogging agent is intended to prevent the development of the unexposed crystals, since a so-called development fog (gray fog) also forms in the unexposed areas.
- Used slowing chemicals
- Potassium bromide ( ), potassium iodide ( )
- The potassium bromide dissociates in an aqueous solution into potassium ions ( ) and bromide ions ( ). The bromide ions counteract the development, as they suppress the concentration of silver ions in the solution according to the law of mass action in chemistry. In general, the bromide ions have a slowing effect on the development process, since they increase the negative charge around the halogenated silver grain and so it is more difficult for the developer ions to reach the development nuclei.
Stop bath or interrupt bath
After the development has ended, the development process should be interrupted. Because the activity of a developer depends on the milieu of its alkali, immediate interruption by an acidic bath can be guaranteed. In addition, the stop bath prevents residues of the (alkaline) developer from increasing the pH value of the fixer and thus extends its shelf life. Suitable is e.g. B. acetic acid in 2% solution, this neutralizes the alkaline developer residues. Because of the dangers posed by acetic acid (development of a vinegar allergy, chemical burns on skin contact, lung damage when inhaling vapors, harmful emissions), citric acid is increasingly used. When using an acidic fixer, the stop bath can in principle be dispensed with.
This process makes the photographic material light-proof. After all, the negatives should be enlarged once. To do this, the unexposed and still light-sensitive silver halides must be removed. Sodium thiosulphate is used for normal fixation baths, and ammonium thiosulphate for rapid fixation baths . However, the fixing process is not a solution process, rather the thiosulphate initially reacts with the silver halide to form insoluble silver thiosulphate , which then gradually changes into a soluble complex:
If the fixing process is terminated prematurely or if the layer in the fixing bath is not moved, the process stops in an intermediate step. Fixing baths are acidified with sodium bisulfite ( ) or potassium disulfite ( ) to protect against fogging, to finally neutralize the developer and also to decolorize the substrate. If acid is carried over into the fixer, depending on the fixer, sulfur dioxide and ammonia are emitted . To protect against health hazards, the stop bath should not be carried over into the fixer, and adequate ventilation should be ensured.
Chromogenic black and white film
As early as 1980, the English manufacturer Ilford launched the XP1, the first chromogenic black and white film. Due to their fundamental photochemical similarity to regular color negative films, chromogenic b / w films can be reliably developed in every minilab in the world with the standard C-41 process - this is an enormous simplification and shortening of the long analogue path to the finished image, which today can hardly be reproduced in today's fast digital photography.
The advantage of the large exposure tolerance of this type of film is offset by the disadvantage of standardized film development, which does not allow any individual development variants with their special possibilities of influence. Like a color negative film, the film contains a pure, fine-grained dye image after laboratory processing; the silver image that emerged during development is removed.
Processing in the C-41 process
- Reduction of silver:
- The developer is oxidized in the process; a developer oxidation product is formed.
- The developer oxidation product reacts with the color couplers to form dyes (yellow, magenta, cyan) in equal proportions (50% yellow + magenta + cyan = gray value, 100% yellow + magenta + cyan = black).
- Bleach bath
The silver is converted back into a silver halide compound in the bleach bath.
The silver salt compound is now made water-soluble and washed out.
Comparable with color film , the term black and white film can also be found for the sequence of moving images made up of the colors white, black and their gray values, for example as a cinema film or other product of film art , but also in black and white television . In this sense, practically all films before the 1930s were black and white films, which were only replaced by color films in the 1950s and 1960s - and from the 1970s also by color television . In artistic photography, color film has never been able to completely displace black and white material, as subtle shades are usually more effective if no additional color information distracts the viewer. In the amateur sector - for vacation photos - black and white film played practically no role even before the spread of digital technology (except in Nina Hagen's GDR hit “You forgot color film”).
Black and white films are still being made today. They are used, for example, when a film deals with interpersonal issues and elaborate color images distract from the often complicated story. Such films often remain specialty films and are shown in art house cinemas, but there are also well-known examples of modern black and white films, for example Schindler's List or Tim Burton's Ed Wood . This film was shot in monochrome to match the time the action takes place. Another example is the film Sin City , which is black and white, but uses some colored details such as eyes, cars or blood (color key technique). As a rule, black and white films allow the scenes to be illuminated with more contrast. This stylistic device is almost inextricably linked with film noir , which is why even today homages to this genre like to do without color film (for example The Good German ). Black and white film is rarely used together with color film in order to delimit different narrative levels, such as flashbacks or a story in the story (for example Stalker by Andrei Arsenjewitsch Tarkowski or the crime scene episode The Oide Depp ). In addition, (economically usable) color film was significantly less sensitive to light until the 1980s, so that in situations where artificial lighting had to be avoided and natural light was insufficient, black and white material remained the only option for technical reasons.
Black and white films require special attention from the cameraman as well as the costume and set designers . Two completely different colors look exactly the same in a black and white image if they have the same gray values. If it is not possible to influence the given body colors, the contrast can be increased in such cases by using colored filters in front of the camera lens or headlights. The cameraman and the lighting technician must take this fact into account in their work and create a high-contrast image so that all the desired objects can be correctly identified in the image.