Saturday, September 12, 2015

Chemicals in Film Processing

Chemicals in Film Processing

A progression of chemicals is used to process photographic film. These chemicals work to create an image on the film and eliminate the film's sensitivity to light so the image can be preserved. A series of chemicals are required for a typical black and white photo process. Color photography uses a similar process with some additional chemicals, because color film is made up of multiple photosensitive layers to capture color ranges.

Developer

    Black and White photographic film is coated with a light-sensitive emulsion containing silver compounds. These compounds change their chemical structure when exposed to light, allowing the emulsion to capture an image. A solution called photographic developer, made up of a sodium sulfite solution, causes the silver that was exposed to light to turn a dark color, with the darkness related to how much light was received. This creates a photographic negative.

Stop Bath

    The reaction between the film emulsion and developer will continue until all of the emulsion has reacted and the negative turns completely black. In order to prevent this, a stop bath is used. Consisting primarily of acetic acid, a common organic compound found in vinegar, the stop bath immediately halts the reaction between the developer and the emulsion, preserving the state of the negative.

Fixer

    Although the stop bath halts the developer reaction, the film is still sensitive to light. Additional exposure to light will cause further reactions of the silver in the emulsion, ruining the negative. Fixer is applied to the negative to remove any remaining silver. Fixer consists of a solution of sodium thiosulfate, aluminum dodecahydrate and several other chemicals. Once the film has been treated with fixer, it is no longer sensitive to light.

Washers, Cleaners, Spot Removers

    After processing is complete, negatives are often treated with cleaners. These cleaners remove traces of photo-developing chemicals and prevent water spots on the negatives. Among the more common are Kodak Photo-Flo, which contains propylene glycol, and Kodak Hypo Clean, a mixture of sodium sulfite, sodium metabisulfite, sodium citrate and EDTA.


Chemicals in Film Processing

A progression of chemicals is used to process photographic film. These chemicals work to create an image on the film and eliminate the film's sensitivity to light so the image can be preserved. A series of chemicals are required for a typical black and white photo process. Color photography uses a similar process with some additional chemicals, because color film is made up of multiple photosensitive layers to capture color ranges.

Developer

    Black and White photographic film is coated with a light-sensitive emulsion containing silver compounds. These compounds change their chemical structure when exposed to light, allowing the emulsion to capture an image. A solution called photographic developer, made up of a sodium sulfite solution, causes the silver that was exposed to light to turn a dark color, with the darkness related to how much light was received. This creates a photographic negative.

Stop Bath

    The reaction between the film emulsion and developer will continue until all of the emulsion has reacted and the negative turns completely black. In order to prevent this, a stop bath is used. Consisting primarily of acetic acid, a common organic compound found in vinegar, the stop bath immediately halts the reaction between the developer and the emulsion, preserving the state of the negative.

Fixer

    Although the stop bath halts the developer reaction, the film is still sensitive to light. Additional exposure to light will cause further reactions of the silver in the emulsion, ruining the negative. Fixer is applied to the negative to remove any remaining silver. Fixer consists of a solution of sodium thiosulfate, aluminum dodecahydrate and several other chemicals. Once the film has been treated with fixer, it is no longer sensitive to light.

Washers, Cleaners, Spot Removers

    After processing is complete, negatives are often treated with cleaners. These cleaners remove traces of photo-developing chemicals and prevent water spots on the negatives. Among the more common are Kodak Photo-Flo, which contains propylene glycol, and Kodak Hypo Clean, a mixture of sodium sulfite, sodium metabisulfite, sodium citrate and EDTA.



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