Dark room - 12.0 Flashcards
What is the purpose of a safelight?
Provides light in the darkrom that does not expose film during processing and handling
What are specifics about safelight that should be considered?
The color of the safelight should consider the spectral sensitivity of the film that is being used.
A normal, silver halide film has light sensitivity to blue wavelength (450-500nm). Safelight should not be blue - but in the brown/amber to red wavelengths (600-750nm)
What are some specific filter specifications for types of film?
Silver halide - blue wavelength (450-500nm) - brown/amber/red (600-750)
Ortho film - film that is used with intensifying screens using rare earth metals (that produce in the green wavelength [500-550nm]), and film is covered in green absorbing dye - require a red safelight (650-750nm)
Pan film - film that is covered in red absorbing dye
What are the 3 zones of safelight in the darkroom?
Brightest - films are washed and placed in dryer (development has already occurred)
Medium - films are developed and fixed
Dim - where films are stored, loaded and unloaded
How is the latent image formed on an emulsion?
Light interacts with the silver halide crystals - releasing a bromide ion and electron
Bromide ion is lost in the emulsion
electron is attracted to sensitivity speck
At the speck - the electron will attract and reduce a silver ion into metallic silver atom
Silver atom acts to further attract electrons and silver ions forming a latent image
What part of a film is developed?
The portions of the film that have formed a latent image
Darker areas - regions with greater # of exposed crystals
Lighter areas - regions with lesser # of exposed crystals (fewer latent image centers)
What happens to the un-exposed crystals
Will be washed away and not developed
However, if left int he developer for a long enough time, some of these crystals will develop
What are the four steps of development?
developer
fixer
washing
drying
What occurs in the developer
Reducing agents serve as catalysts to reduce the remaining silver ions in the crystals that have latent image centers
What are the components of the developer solution?
Developers: hydroquinone and phenidone Activators: NaOH Restrainers: Potassium halide (KBr, KI) Preservative: sodium sulfite Hardener
What does each component of the developer solution do?
Develop: catalyze reduction of silver ions
Activator: maintains pH of the solution (basic)
Restrainer: prevents unexposed crystals from developing
Preservative: prevents oxidation by free oxygen in the air
Hardener: controls swelling of the emulsion
What are the components of the fixing solution?
Activator: Acetic acid
Clearing agent: ammonium thiosulfate ‘hypo’
Hardener: KCl
Preservative: Sodium sulfite
What does ech component of the fixing solution do?
Acetic acid: stop bath - prevents further reduction of silver ions (neutralizes the base)
Clearing agent: removes unexposed silver halide crystals
Hardener: shrinks, hardens the emulsion
Preservative: prevents oxidation of chemicals from room xygen
What is the replenisher?
Replenishes chemicals after each use.
The amount that is replaced depends on the size of the film, optical density of the film etc.
What are optimal storage conditions for un-exposed film?
10-20C
