Film Processing

FILM PROCESSING

Manual processing

• Automatic processing

FILM PROCESSING

AUTOMATIC PROCESSING

• Four Automatic processing stages
• Development
• Fixing
• Washing
• Drying

MANUAL PROCESSING

• Manual processing stages
• Development
• Rinsing
• Fixing
• Washing
• Drying

LATENT IMAGE

Electrons (released by light from bromine ions) are trapped

Positive silver ions are trapped at the sensitivity speck by the negative charges on the electrons Positive charges on the silver ions are neutralized by negative charges on the electrons and silver atoms form

RE:

• The effect on photosensitive materials (emulsion – Silver
• halides) of exposure to light or X-ray radiation is to produce
• an invisible latent image within the emulsion.
• The emulsion of X-ray films must be chemically processed to
• render visible and permanent the information recorded in the
• latent image.
• Film processing involves a number of complex chemical
• reactions whose activity and efficiency are influenced by
• various factors, including the temperature and acidity or
• alkalinity of the chemical environment in which the reactions

take place.

Temperature is quoted in Celsius (ºC)

• Acidity/ alkalinity is expressed using the pH scale.
• The pH scale
• Is used to express the degree of acidity or alkalinity of a solution.
• It is based on a measure of the concentration of the positively
• charged hydrogen ions in a solution.
• -In a neutral solution, such as pure water, these ions are present
• in equal numbers at a concentration of 10ˉ⁷ mol/l (moles per liter)
• -Increase in the concentration of hydrogen ions to > 10 ˉ⁷mol/1.
• The solution is then said to be acidic.
• -Concentration of hydrogen ions to < 10ˉ ⁷mol/l and the solution is

then alkaline.

PROCESSING CHEMICAL

• May be purchased in a variety of ways (liquids or powders).

May be in concentrated form and need to be diluted or mixed.

Preparing chemicals correctly is important or resulting solution may adversely affect the radiographic product.

• Chemicals should be kept at specified room temperature.
• Variances may adversely affect the radiographic product.
• Too low temps, some of the chemicals may become sluggish in action and produce an under-developed or under-fixed radiograph.
• Too high temps, may be too hot for manual control.

All chemicals should be kept at same temperature.

Variances in temperature between the chemicals can result in film reticulation.

• Reticulation- a darkroom artifact produced by variable chemical temperatures that cause irregular expansion and contraction of the film emulsion, resulting in a mottled density appearance

PROCESSING CYCLE

• Manual
• processing
• Development
• Rinsing
• Fixing
• Washing
• Drying
• Automatic
• processing
• Development
• Fixing
• Washing

Drying

PROCESSING CYCLE

MANUAL

• Exposed film
• Dev.
• Rinse
• Fix
• Wash

Dryer

PROCESSING CYCLE

AUTOMATIC

• Exposed film
• Dev.
• Fix
• Wash

Dryer

DEVELOPMENT

Its primary purpose is convert latent image into visible image During development the exposed silver halide grains are reduced to metallic silver while unexposed remain unchanged A chemical fog is produced by poor developer acting on unexposed grains

CHEMICAL ACTION OF DEVELOPER

Development is a process of chemical reduction;

• This reduction is achieved by developer donating electrons to silver ions in the grains, thus neutralizing their positive charge and converting them to metallic silver

Both exposed and unexposed silver bromide grains are surrounded by –ve charge barrier of bromine ions employed during emulsion manufacture.

CHEMICAL ACTION OF DEVELOPER

• The emulsion becomes wet
• Chemicals penetrate in to the emulsion
• A process of chemical reduction takes place
• Developer donates electrons to the silver ions in the exposed silver bromide grains

Silver ions by obtaining electrons is converted into metallic silver

Charge barriers;

Both exposed and unexposed silver bromide grains are surrounded by a negative charge barrier of bromine ions created by the excess of potassium bromide employed in the synthesis of silver bromide during the manufacture of emulsion The charge barrier normally protects the silver bromide from attack by electrons in the developing solution Exposed silver bromide grains posses a weakness in the charge barrier caused by the presence of neutral silver atoms which have collected at the sensitivity speck

EFFECTS OF THE BY-PRODUCTS OF

DEVELOPMENT

With continuous use, the developer becomes depleted of electrons and it is said to be oxidized and reduced in activity The remaining negative Bromine ions react with positive hydrogen ions in the solution to form hydrobromic acid.

• This causes the pH to fall and reduces the developer activity

The atmospheric oxygen also cause developer oxidation and reduce activity

CONSTITUTION OF DEVELOPER

SOLUTION

In automatic processing the solution added to the working developer in the tank is called developer replenisher When the developer tank is emptied and fresh solution is added the activity of the replenisher is modified by adding a chemical called the starter solution The developer in automatic processing and manual processing are different in several aspects

Developer replenisher

• +
• Starter

Working developer

CONSTITUENTS OF DEVELOPER

REPLENISHER SOLUTION

• Solvent
• Developing agent
• Accelerator
• Buffers
• Restrainers
• Preservative
• Hardener

Sequestering agents

SOLVENT – water

• Functions
• Acts as the carrying medium in which the developer constituents are dissolved.

Provides a means of controlling the developer activity by diluting its effects.

Has a softening effect on film emulsion to allow the chemicals to penetrate into the emulsion and reach AgBr grains (The water should be clean enough not to have any chemical reaction with the developer constituents It should not contain mud & dirt or particles which may cause damage to the delicate film emulsion)

DEVELOPING AGENTS

• Are reducing agents which supply electrons
• Should exhibit the following properties
• -Must be selective and distinguish between exposed and unexposed grains
• Sufficiently high activity
• As resistant as possible to the presence of bromine ions in the solution
• No Single reducing agent which satisfies all of these requirements

Therefore combinations are used

DEVELOPING AGENTS

• Metol and Hydroquinone
• (MQ) were use in early manual
• developers
• Phenidone and Hydroquinone
• (PQ) are used in modern automatic processing

PHENIDONE

• Phenidone = 1-pheyl-3-pyrazolidone
• Quick acting
• Selectivity low
• Mildly sensitive to bromine ion in concentration

Produces low contrast characteristics

HYDROQUINONE

• Requires a strongly alkaline medium in which to act
• More selective than phenidone
• Slow to start the development action
• But once started acts rapidly on exposed AgBr grains
• Does not affect lightly exposed or unexposed grains

Produces high contrast characteristics

Advantages of PQ developer

When phenidone and hydroquinone are together in one developer their characteristics complement each other Therefore PQ developers have the following advantages over the other developers Tolerance of increase in bromine ion concentration High selectivity and low chemical fog Adequate activity even in low concentration

Advantages of PQ developer

• Available in liquid concentration form
• Fast acting permitting complete development in 20-30 seconds

Adequate contrast characteristics

Super-additive effect (the reducing effect of combination is much greater than the sum of the effects they produce when used separately

NB;

DENSITY;

• Amount of darkness in the radiographic image.
• Also known as transmitted density.
• >>> We have air density, bone density, water density (soft tissue) metal density

CONTRAST;

• Density difference between neighboring regions on a

plain photography.

Super-additive effect

The shape of the characteristic curve is controlled by the two developing agents

• Hydroquinone only
• Phenidone only
• Combine effect
• Optical density

Exposure

Accelerators

• PQ developers need an alkaline medium to operate (pH between 9.8- 11.4)
• It is established by adding a strong alkali

Usually Potassium carbonate or Potassium hydroxide is used The alkali is known as accelerator since its function is to accelerate the developing process

PH and development

• The pH of the developer has a marked effect on its activity and on image contrast:
• Low pH – low activity and development sluggish
• High pH – high activity and chemical fog
• The range of pH values for different developers will vary from 9.8 to 11.4

However for a particular developer the pH should not vary

Buffers

A buffer is a chemical compound which has the effect of maintaining the pH of a solution within close limits Potassium sulphite used as the preservative and the potassium carbonate used as accelerator provides an adequate buffering action

Restrainers

Modifies the behavior of developing agents so that they become more selective That is to reduce the tendency to convert unexposed silver halide grains to metallic silver and therefore to prevent chemical fogging KBr-The developer by product will act as a restrainer In PQ developer benzotriazole is used as a restrainer and an antifogging

Preservatives

• To check oxidation of developing agents by the action of atmospheric oxygen
• Additionally it permits more efficient regeneration of Phenidone by hydroquinone

Potassium sulphite is commonly used

Hardeners

To prevent excessive swelling of the emulsion by the absorption of water which is pronounced in the alkaline developer Powerful hardeners like glutaraldehyde may employed – they are more effective in alkaline developer But manufacturers use alternatives because of its undesirable allergenic effects Manual processing does not need hardeners

Sequestering agents

These are chemicals which prevent precipitation of insoluble mineral salts which tends to occur in hard water They act by combining with the minerals to form soluble compounds which do not react with the developer chemicals Compounds based on EDTA are commonly used

Other constituents

• Bactericides and Fungicides
• These inhibit the growth of organisms in the solution and in containing vessels.

Starter solution

• The starter solution is added to the fresh solution in

the developer tank at the start

To reduce the initial activity of the developer to the safe working level by bringing down the pH to the correct value It is an acidic restrainer which provides KBr until the development process produce its self restraining effect Developer replenisher + starter = working developer Manual processing does not use starter solution

Efficiency of development & Factors affecting development

• How is the efficiency of development measured? Or assessed?
• -Assessing the optical density
• -Assessing the contrast
• Factors influence the quantity and quality of development are;
• Constitution of the developer
• -Temperature of the developer
• Development time

How Constitution of the developer

• affect development?
• The activity of the developer depends on
• -Type of developer
• Concentration
• pH
• Concentration of restrainer & anti-foggant
• The developer activity reduces with use because,
• The concentration of developing agent and
• pH drops, while the concentration of

restrainer increases

Therefore the developer has to be replenished continuously if the activity is to be maintained

• The rate of replenishment depends on;
• The area of film processed
• Type of emulsion
• Type of image
• Aerial oxidation
• Not only the activity but the volume of developer also is reduced
• with use because of;
• The developer carry over
• Evaporation
• Gelatin of emulsion absorption

Developer adhering to the film surface

HOW DOES DEVELOPER TEMPERATURE

AFFECT DEVELOPMENT?

• The developer activity increases with temperature
• The temperature has to be controlled and maintained if development is to be standardized
• Methods used – temperature & cycle times
• High temperature development ; 38 – 42 0 C , 90S
• Low temperature development : 20 – 30 0 C, 7m -90s

Medium temperature development ; 37 – 33 0 C, 90s-160s

Effect of increase of temperature

A slightly increased temperature (0.5 0C) without compensating reduction of development time results in:

• Increased image density for the same exposure
• Slightly increased chemical fog
• Increased image contrast
• A more severe rise in temperature (several degrees) initially leads to
• Gross increase in density
• Unacceptably increase in chemical fog
• Reduction in contrast

Effect of increase of temperature

Effect of decrease of temperature

• A slightly lowered temperature will result in:
• Decreased image density for the same exposure
• Slightly reduced chemical fog
• Reduced image contrast
• A more severe fall in temperature will result in:
• Gross overall reduction in density
• Loss of contrast and reduced D-max

Effect of decrease of temperature

Developer temperature in manual processing

Manufacturers of manual processing recommend a temperature of 20 0 C for optimum result. But they provide acceptable results two or three degrees high or low provided the developing time is adjusted accordingly

Development time

This is the time the film is kept in the developer In automatic processing it may be defined as the time interval which elapses between the entry of a specified part of a film (e.g. leading edge) into the developing solution and the exit from the developing solution of the same part of the film.

• It varies with the full cycle time of the processor
• 7 m ——– 130 s
• 3 ½ m ——- 68 s
• 110 s ——— 30 s

90 s ———- 26 s

Development time is determined by:

• Developer concentration
• Developer temperature
• Film type
• Agitation of developer solution
• Agitation of solution in automatic processing is achieved by
• Film motion
• Rotation of rollers
• Circulation of developer

Summary

• Development is the most important part of processing
• The quality of the recorded image greatly depend on development
• To maintain standard development following has to be maintained as constant as possible
• Developer concentration
• Constant temperature
• Constant time

FIL MP ROCESSING

FIXATION

• Fixation has four major functions

To stop further development

To fix the image i.e. Render it chemically stable so that it does not undergo further changes and no longer photosensitive To complete the process of hardening of the film emulsion To clear the image by removing the remaining silver halide from the emulsion

Stopping further development

Achieved by making the fixing solution acidic (pH between 4.0 – 4.5) Phenidone hydroquinone developing agents only operate in an alkaline environment; thus any further development is inhibited as film enters the fixing solution Intermediate rinsing stage between developing and fixing fulfils this function in manual processing

Fixing the image

Process of clearing is also the process of fixing the image Hardening the emulsion:-Ensures the gelatine does not absorb too much water and thus minimizes drying time.

Also toughness emulsion and protect it from chemical damage during washing & drying stages of processing.

Cleaning the image:- Only about 40% of silver halide in the film emulsion is converted to silver during development

Film Processing

During process of fixation the undeveloped halide grains 60% are converted into soluble compounds which then dissolved out of the emulsion into fixing solution. Thus the unexposed parts of the image become transparent and milky appearance is lost Clearing time is the time taken for the image to lose its milky appearance

Constituents of fixing solution

• Solvent
• Fixing agents
• Acid
• Hardener
• Buffer
• Preservative

Anti- sluing agent

Solvent :- Water

• Is the solvent and diluents used in fixing solution
• Acts as a carrying medium for the active constituent in fixer

Provides a means of controlling the activity by diluting its effects.

Fixing agents

Fixing agents:- Are chemical which combine with insoluble halide in the film emulsion to form solution compounds which diffuse and can be washed out of the emulsion Ammonium thiosulphate is supplied in liquid concentration while Sodium thiosulphate is in powder form and used in manual processing

Chemical reaction that occurs in fixer

Silver bromide + Ammonium thiosulphate > Ammonium salt of monogento- dithio- sulphuric acid + Ammonium bromide Compound formed are soluble in water and be removed by washing.

Silver bromide + sodium thiosulphate > sodium salt of monoargento- diothio- sulphuric acid + sodium bromide Compound formed is soluble in water and can be removed by washing

Advantages of Ammonium thiosulphate over the sodium thiosulphate

• Highly soluble, thus its available in liquid concentration
• Highly active , thus fixing can be done rapidly e.g. 15sec in 90 sec processing cycle

Its by products is highly soluble hence readily washed out of the film emulsion

Acid

Stops development as soon as film enters the fixer Avoid staining of the image dichronic fog –which give yellow green blue tinged stain when the image is viewed by reflecting light and tinged pink when view by transmitted light.

• Also provide suitable environment for the hardening agent to fixer.

Acetic acid is used; pH 4.0-4.5

Hardener

• Limit water uptake by emulsion layer: hence
• reduces drying time

ii) prevents physical damage to the emulsion surface

Three Hardening agents used for fixing

• Chrome alum (chrome potassium alum)

Its efficiency last for few days; whether in use or not. Therefore it’s suitable be used soon after preparation

• Works better in pH range of 3.5- 4.7 low pH

cause sulphurization- process of sulphur

2) Potassium Alum

• It retain its hardening properties well with time
• Works well at higher pH from 4.5-4.9
• Ph beyond 5.5 causes precipitate of aluminium hydroxide with potassium alum hardener ( a white bloom) may appear on film

3) Aluminium chloride (Aluminium sulphate)

• Used with rapid ammonium thiousulphate fixers and allows hardening to be completed in very short time

-The optimum pH for hardening action is 4.1 to 4.4

BUFFER

• Prevent sulphurization
• ii) Ensure neutralization of developer

iii) Maintain optimum hardener activity Fixing solution should be buffered against neutralization effect of alkaline developing solution carried by films from the developing tank Chemical used is Sodium acetate with Acetic acid Manual processing rinse reduce developer carry-over into fixing solution.

PRESERVATIVE

• Slow the decomposition of thiosulphate delays the onset of sulphurization

Chemical in use is sodium sulphite

Anti-sludging agent

Aluminium salt used as a hardener have tendency to produce insoluble aluminium compound.

Which precipitate out of solution and form sludge which adhere to the films & to the side of the fixing tank To reduce the formation of sludge boric acid is included as an anti sludging agent

FACTORS AFFECTING FIXATION

• The process of fixing a film material occurs in three
• stages
• The fixing solution diffuses into the film emulsion

ii) The fixing agent reacts chemically with the silver halides in the emulsion iii) The resulting soluble silver complexes and halide dissolve and begin to diffuse out of the emulsion Constitution of fixing solution;

-The activity of fixer at a given temperature depends on a number of aspect relating the chemical composition of the fixing solution

Fixing agents:- Ammonium thiosulphate gives a rapid acting higher energy fixer

Concentration of fixing agent in solution:- Activity increases with concentration.

• As film pass through fixing tank fixing agent is used up in the reaction with silver halides
• Fixing agent is also lost due to carry over of fixing solution during the transfer of films to wash tank.

3.Presence of hardener:- Slow down the fixing process but speed up the drying process

4.pH of fixing solution:- carry over of alkaline developing solution tend to neutralize the acid fixer, causing pH to rinse. Accurately controlled replenishment ensures a stable fixer pH.

5. Types of film material

• Area of film processed:- The volume of replenishment required is proportional to the area of film & also the size and number of films processed
• Type of emulsion:- More fixing agent is needed to process direct exposure x ray film than screen type because the emulsion has a higher coating weight.
• Rapid process film incorporate thin emulsion which can be penetrated rapidly by processing chemicals

Film Processing

• Type of image:- A lightly exposed film contain more unexposed silver halide grains than a similar film which has received greater exposure.

Thus after development there is more silver halide to be cleared , more fixing agent is used and more fixer replenisher is necessary

Film Processing

• Fixer temperature:- Activity of fixing agents increase with temperature and at higher temperatures diffusion processes are more rapid

Too great difference in temperature between developer and fixer results in film reticulation (cracking of film)

• Agitation of film:- vigorous agitation accelerates fixation by speeding the removal of by products from the film emulsion and their replacement with fresh fixer

Factors affecting fixer replenishment rate

Area of film processed: as with developer, the volume of replenisher required is approximately proportional to the area of film and therefore depends on the size and number of films processed.

Type of emulsion: more fixing agent is needed to process a direct-exposure X-ray film than a screen-type film because the emulsion has a higher coating weight. 136 The Radiograph (III) Type of image: a lightly exposed film (or a tightly collimated film) contains more unexposed silver halide grains than a similar film which has received a greater exposure (or been less well collimated). Thus, after development there is more silver halide to be cleared, more fixing agent is used and more fixer replenisher is necessary.

Maintenance of fixer volume

• A small volume of fixing solution is lost due to carry over
• whenever a film leaves the fixing tank, and a similar
• volume of solution is gained due to carry-over on films
• entering the fixing tank from the developer.

The net change in volume from carry-over is therefore not significant.

Other fluid losses occur, however, due to evaporation and the deliberate bleeding off of solution to remove contaminants.

Maintenance of fixer volume

• When film leaves fixing tank small volume is lost due
• to carry over and similar volume of solution is gained
• due to carry over on film entering tank from

developer.

Fixer replenishment ensures that lost chemicals are replaced and contaminated removed hence optimum quality films are produced

Fixing time

• Maximum time for developer to diffuse out of the film
• -Fixer solution diffuse in and processes of clearing and
• hardening completed
• Factors affecting fixing time;
• Fixer activity
• Fixer temperature

Agitation of fixing solution

FACTORS AFFECTING FIXING TIME

• (1)Fixer activity; The higher the fixer activity, the shorter is the
• required fixing time. We have seen that fixer activity depends both

on the constitution of the fixing solution and on its temperature.

(2) Type of film emulsion; Rapid-process films incorporate thin emulsions which can be penetrated rapidly by the processing chemicals. Direct-exposure film, which has a thicker emulsion, may cause problems during a rapid fixing stage. Silver iodide reacts more slowly with fixing agent than silver bromide and it may be necessary to use a cycle time of 3 or 3½min rather than 90s to process such film successfully.

(3) Agitation of fixing solution; As with development vigorous agitation accelerates fixation by speeding the removal of by-products from the film emulsion and their replacement with fresh fixer. third stage: washing.

RINSING, WASHING & DRYING

Intermediate Rinse or stop bath:- Stage in the processing cycle which is between development and fixing in manual processing.

PURPOSE OF INTERMEDIATE

RINSING IN MANUAL PROCESSING

• Slow action and remove developer from
• surface of film
• Stop action of the developer by
• neutralizing effect (Achieved by putting

film in an acid solution e.g. Acid stop bath)

METHOD OF RINSING

• Plain rinse can be;
• A static bath- Just tank full of water
• ii) A spray rinse –Fresh water provided by a
• number of jet directed in the film
• iii) Running rinse- Flow of water through tank,
• water entering at low level and leaving at top

of fixing bath

EFFECT OF INADEQUATE RISING

• Presence of developing agents in fixing bath
• results in:-
• Dichronic fog
• Increased alkalinity of the fixing bath

Brown stain which result from oxidized developer

WASHING

• When film comes out of fixing bath it carries in its
• emulsion layer the following;
• Argento- thiosulphate -which has been formed in the
• chemical action of the fixer
• ii) Residual of fixing agent

iii) Remaining salts which are other constituent

EFFECT OF INADEQUATE WASHING

• Colourless argento-thiosulphate decompose after a while to from silver sulphide which produces yellow brown stain
• Residual fixing agent decomposes and produce substances which attack silver image and form silver sulphide results in yellow brown stain and lost of image
• Residual salts crystallizes on film surface making interpretation difficult.

N/B Tap water wash control Yellow brown sulphur stain

DIFFUSION

Transfer by diffusion of chemical from the emulsion gelatine to wash water occur in the concentration gradient Washing efficiency:-The level of contamination should be reduced to the point where no image staining occur.

In 90 sec cycle processing, about 15 sec is allowed for washing stage while in manual processing 10 min

FACTORS AFFECTING WASHING

EFFICIENCY

a)Film emulsion:- Thick emulsion takes longer to wash than thin one Hardening of emulsion inhibit diffusion but also shortens diffusion path by reducing emulsion thickness

• Condition of fixing solution :- To avoid in adequate washing it is important to maintain fixer in optimum condition by correct replenishment

c) Condition of washing water:- Wash water should be replaced frequently with fresh water

• Agitation:- Ensure fresh water is being forced against the emulsion surface and contaminated water carried away.

This maintain concentration gradient needed and its efficient diffusion

• Washing time:- Duration taken for level of residual containments in a film emulsion to reduced to acceptable level

Film Processing

• Temperature of wash water:- washing efficiency increases with temperature because surface tension of water is reduced and its penetration into emulsion is accelerated

DRYING

• The final stage in processing of radiograph is to remove all water

surface and most of that retained in the emulsion to 10-15% In automatic processing surface water is removed by squeegee rollers while evaporation removes water from emulsion In 90sec processing cycle 25sec is allows for drying stage Three important feature in drying photographic film by air;

• The temperature of the air
• ii) The humidity of the air

iii) The flow of air past the emulsion

Raising temperature of the air increases the rate at which moisture evaporates from gelatin and thus shortens drying time

• Drying temperature is governed by:-
• By amount of drying to be done
• By length of drying time

FACTORS AFFECTING DRYING TIME

Depends upon two factors

• The wetness of the emulsion:- Volume of water retained in the emulsion per unit area of its surface

Depends on two factors

• Hardness of emulsion – hardened emulsion retains less water than a soft emulsion and therefore can be dried quickly
• Emulsion thickness – thin emulsion retain less water than thick one
• Direct exposure x-ray film take longer to dry than screen type of x-ray film

2) The drying condition:- The drying medium is Air.

• The speed at which air cab evaporate moisture from the emulsion depends upon
• Air humidity:- Dry air accelerates the evaporation process and reduces drying time

Relative humidity should not be greater than 60%

• Air temperature:- Heated air can retain more moisture than cold air and therefore more effective drying medium

Air temperature should be between 40 & 60%

Film Processing

• Air circulation:- As moisture evaporate from the emulsion air around the emulsion becomes more humidity; this humidity air should be replaced with drier air by using an air circulation system.

DEVELOPER CHEMISTRY FOR AUTOMATIC PROCESSOR

PHENIDONE

• Quickly build up gray tones in the image
• Reducing agents convert exposed silver into black metallic silver

DEVELOPING AGENTS

HYDROQUINONE

• Slowly build up black tone and contrast in the image

ACTIVATOR

SODIUM CARBONATE

• Swells and softens the emulsion so that reducing agents work more effectively
• Provides required alkalinity for reducing agents

HARDENER

GLUTERALDEHYDE

• Controls emulsion swelling to allow better transportation of film through the processor

RESTRAINER

POTASSIUM BROMIDE

Restrains reducing agents keeping unexposed silver halide from being developed

FIXER CHEMISTRY FOR AN AUTOMATIC PROCESSOR

FIXING AGENTS

AMMONIUM THIOSULPHATE

• Dissolve silver salts in unexposed areas

NEUTRALIZER

ACETIC ACID

• Neutralize alkaline developer carried over from developing solution

HARDENER

ALUMINUM CHLORIDE

• Restrains swelling of gelatin and hardens emulsion

APRESERVATIVE

SODIUM SULPHATE

• Prevents oxidation and discoloration of fixing agents

SOLVENT

• WATER

Liquid for dissolving chemicals

END OF CHAPTER QUESTIONS

• Mention the 4 major functions of fixation outlining how each function is achieved.
• Outline the significance of each constituent of fixing solution.
• Give examples of chemicals used in each constituent of fixing solution
• The process of fixing occurs in 3 stages. Briefly describe each stage.
• Outline the 7 factors affecting fixation.
• Mention the factors affecting fixer replenishment rate

Outline the 3 factors affecting the fixing time

List 2 purpose of intermediate rinsing stage in manual processing

• Outline the 3 methods of rinsing in manual processing
• List 3 effects of inadequate rinsing
• Describe the purpose of washing stage
• What are the effects of inadequate washing
• List 6 factors affecting washing efficiency
• Describe the significance of drying stage
• What are the 3 important features in drying the film by air?

Outline the factors affecting drying time