The Film Developing Process Explained
- Film developing relies on the reaction of certain chemicals to light. A roll of photographic film is coated with layers of silver metal halide, a chemical compound that when exposed to light, forms silver crystals. A developer solution converts the crystals into pure silver. The unexposed halide crystals are washed away in a chemical fixer bath. The remaining silver is now "fixed" to the negative film, leaving dense areas where more intense light struck the film.
- "Film" is a sheet of plastic that is coated with light sensitive materials. The base is made from a liquid material called "dope" and is spread out in extremely thin layers onto a turning wheel. As the wheel turns, the solvents in the dope dry out and a long sheet of plastic cellulose acetate is left over.
- Emulsion is a light sensitive material spread onto the dope to create photographic film. It is made of layers of gelatin with silver metal halide crystals suspended in them. Once the emulsion has been heated and attached to the film base, it is sensitive to light. The size of the crystals and the spacing in between them determines how sensitive the emulsion is to light.
- In a darkroom, the film canister with the exposed film is opened using a can opener and transferred to a light-proof film developing tank. The tank has a reel onto which you thread the unprocessed film. This reel allows the chemicals to cover all surfaces.
- Once the film has been loaded onto the reels, it goes through a series of water washes and chemical baths. The chemicals react with the silver halide crystals, embedding some into the gelatin while washing others away.
The developer bath embeds the silver crystals that were exposed to light into the gelatin, making them permanent. The excess halide crystals are washed away in a second fixer bath. This leaves behind a negative image, denser where the light was stronger, lighter where the light was less intense. - The post processing phase consists of treating the film with a wetting agent to prevent water spots, drying it on a rack or in a film dryer, then cleaning the film of dust and particles with a brush and lens cloth.
The Science Behind The Process
Film Base
Film Emulsion
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Developing
Post Processing
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