Outline of the Photographic Process

Silver-based photographic materials (for both black and white and colour) consist of mixtures of solid crystals of silver chloride, silver bromide or silver iodide (the exact mix depends upon the product) suspended in gelatine and coated on a film or paper support.   The processing of photographic films and papers consists of two or three basic steps:

• Development: of the images.
• Fixing: removal of some or all of the silver, depending on the process concerned.
• Washing: finally, the image is stabilised by rinsing residual thiosulphate and silver thiosulphate complexes out of the emulsion layer with water.

  In the case of “washless” processing of colour materials, a chemical stabiliser solution replaces the water.

The Colour Photographic Process

Colour photographic materials include the majority of amateur and professional films and papers, motion picture films and some graphic arts products.

• Developer: metallic silver is formed in the image areas along with a dye. 
• Bleach: the metallic silver produced in the development step is then converted to crystals of silver bromide or silver chloride.
• Fixer: the silver chloride or bromide is removed as a soluble thiosulphate complex in a solution. 

  In most colour paper processes, the bleach and fix baths are combined into a single solution called a bleach-fix. 

In colour products, virtually no silver remains in the film or paper after processing.

In processing colour photographic materials, the exact process will vary depending on market demand, imaging media and application.  Hence, every system will have local variations that need to be understood.

Typical Colour Photographic Processing Equipment

Typical Colour Minilab Film Processor

N1 - Developer N2 - Bleach N3 - Fixer NS - Super Rinse / Stabiliser

Typical Colour Minilab Printer-Processor

P1 - Developer P2 - Bleach Fix P3 - Super rinse

The Black and White Photographic Process

The black and white process has been around for well over a hundred years, in one form or another. It includes X-ray, graphic arts, microfilm and general-purpose operations.

It has the same 3 processing steps mentioned above, namely developing, fixing and washing.

There are now 2 main types of black and white material:

• Traditional silver materials where a substantial amount of the original coated silver (usually converted to metallic silver) remains in the film or paper after processing.
• Materials based on colour technology where the final image is composed of dyes instead of silver. These use the colour processing technology outlined above.

Unlike colour processes there are no standardised processes for traditional black and white processing.

There is wide variation in the composition and volumes of liquid waste from such processes. The manufacturer or supplier of the chemical products can usually provide more information on typical waste composition although this will vary with each installation.

There are many types of processing machines in use for black and white processes. A typical roller transport machine is shown here.