dark room basics

1. DARK ROOM
DR.ROHAN JOHN JACOB

2. WHAT IS A DARKROOM ?
• Enclosed area or chamber dimly lit by safelight
(usually red) but otherwise intentionally
lightproof room where films are handled and
processed.

3. DARK ROOM LAYOUT
• A room should be set aside as a permanent dark
room, ideally with a floor area of not less than
10sq. m.
• The room must be capable of being made
completely lightproof.
• It should not be damp or subjected to extremes
of temperature.
• Water and electrical outlets should be provided.
Sufficient space to accommodate a dry bench , a
wet bench and a sink.

4. DARK ROOM LAYOUT
[contd.]
• Too large room is as undesirable as small room.
Should be near the x-ray examination area.
• Should be well ventilated.
• The wall should be constructed of solid concrete
(15 cm thick), have a lead box inside to store
boxes of unexposed films currently in use.
• The walls and roof should be painted by white
or cream enamel as such a paint acts as a good
reflecting surface for safe light.
• X-ray rotating warning light in hallway switched
"on" signaling that x-ray machine is operating.

5. LOCATION
• Centrally located
• Serviced by hatches from the adjacent
imaging room
• Away from damp or hot areas
• Accessible in terms of power and water
supply
• Adjoining viewing room

6. SIZE
• Minimum floor area of 10 sq meter
• Ceiling height of 2.5 - 3 meter
• Size may be reduced depending on the
department needs.

7. LIGHT PROOF
• The first requisite of a processing room is the
exclusion of all external white light when
radiographs are processed.
• Photosensitive crystals in film emulsions are
extremely sensitive to visible light, and any
light leaking around a door or window may fog
and ruin the films.

8. LIGHT PROOF
[contd.]
• A door that can be locked to avoid accidental
exposure of film to white light.
• Alternatively a light outside the door
indicating that the darkroom is in use.
• When the white light in the darkroom is
switched off, the indicating light outside
automatically goes on.

9. RADIATION PROTECTION
• Walls adjacent to the radiographic room
should be shielded with correct thickness of
the lead all the way to the ceiling.
• In the interests of both darkroom staff and
film material alike .
• 1.6 mm lead is mostly used.

10. FLOORS
• Non-porous flooring
• Non-slip flooring
• Chemical resistant
• Stain proof
• Durable & easy to maintain
• Light coloured (low- light working conditions)
• Asphalt tiles
• Porcelain tiles
• Clay tiles
• Plastic tiles may be used in the dry dark- rooms

11. WALLS/CEILING
• Light in colour to reflect as much light as
possible onto the working surface .
• Easy to wipe or clean.
• Covered with chemical resistant materials .
• Special paints, varnish, ceramic or plastic wall.

12. VENTILATION AND HEATING
• Satisfactory working conditions for the staff
• Good film handling and storage conditions
• Efficient automatic processor performance
• Relative humidity is maintained at around 40-
60 %
• Room temperature maintained between 18-
20 degree celsius

13. VENTILATION AND HEATING
[contd.]
• A minimum of 10 air changes per hour
• All of these conditions can be achieved by
using a good air-conditioning system
• Alternatively, fairly satisfactory ventilation
can be achieved by using an extractor fan
sited higher than and diagonally opposite a
second fan, the latter being placed so as to
obtain fresh and filtered air from outside.

14. TYPES OF ENTRANCE
• SINGLE DOOR SYSTEM
• DOUBLE DOOR SYSTEM
• MAZETYPE ENTRANCE
• LABYRINTH
• ROTATING DOOR SYSTEM

15. DARK ROOM ILLUMINATION
• WHITE LIGHTING
• SAFELIGHTING

16. WHITE LIGHTING
• For inspection & maintenance of cassettes &
screens
• Cleaning of work surfaces
• Servicing of equipment
• Sited close to the ceiling
• Moderate in intensity (60w tungsten, 30w
fluorescent )
• Preferably centrally placed

17. SAFE LIGHTING
• DIRECT SAFE LIGHTING:
• Light from safe lamp directly falls onto the
work surface
• Eg. Beehive safe lamp
• Minimum distance of 1.2 m/ 4 feet from the
working surface
• Best for loading & unloading areas

18. INDIRECT SAFE LIGHTING
• Directs the light towards the ceiling which
reflects light back into the room
• Is intended to provide general illumination of
the dark room
• Suspended at least 2.1 m above floor level

19. SAFE LIGHT FILTERS
• Sheet of gelatin dyed to the appropriate
colour and sandwiched between two sheets of
glass for protection
• Used in conjunction with a 15W lamp
• Extremes of heat and temperature
deteriorates the filter gelatin
• Should be cleaned periodically

20. How Does A Safelight Work?
• When white light is passed through coloured
filters, certain wavelengths (or colours) are
absorbed by the filters, whilst those wavelengths,
which correspond to the colour of the filters will
be transmitted.
• Making the correct selection of safelight filter
(matching the filter to the film), means choosing
a filter, which will transmit a colour to which the
film is relatively unresponsive, whilst stopping all
light to which the film is most sensitive.

21. WHICH COLOUR FILTER TO USE?
• X-ray films have the highest sensitivity to the
blue-green part of the light spectrum .
• The X- ray film is less sensitive to light in the
opposite region of the spectrum - i.e. the
yellow and red region.
• It is obvious that the blue filter cannot be
used, neither a green color filter as it is so
close to the blue. Therefore safelights are
safest when made with amber or red filters.

22. How Safe Is Safe Lighting?
• No safe lighting is completely safe; all films will
become significantly fogged if exposed to
safelights for long enough.
• This is because safelight filters are not perfect
absorbers of the undesirable wavelengths and, in
truth, all films have some sensitivity to all
wavelengths.
• Thus, the intensity of illumination and the film-
handling time must be kept to a minimum if
significant fogging is not to occur.

23. Safelight illumination test
• Place a coin on a small piece of photo paper.
Let it sit for 20 min. and develop the paper. If
you see the outline of the coin, your safelight
isn't safe. If the safelight is not safe, you
should do one of the following to correct the
problem: 1. Replace the bulb with one of
lower wattage 2. Raise the safelight lamp
higher from working surface 3. Check the filter
- may be cracked or broken.

24. DARK ROOM EQUIPMENTS
• Automatic processor
• Manual processing unit
• Processing chemicals
• Hangers for suspending film
• Cassette
• Film storage hopper
• Loading bench
• Cupboards

25. Chemical sensitization
• Chemical sensitization of the crystals are
produced by adding allylthiourea, a sulfur
containing compound to the emulsion , which
reacts with silver halide to form silver sulfide.

26. Sensitivity Speck
• This Silver Sulfide is usually located on surface
of the crystals and is referred as “sensitivity
speck”.
• The sensitivity speck
traps the electron and
forms the latent image.

28. • The film is then passed through the following
four steps:
• Developing
• Fixing
• Washing
• Drying

29. Development
• It is the first stage in processing of the
radiograph.
• Amplifies latent image by 100,000,000!
• The primary purpose: convert the invisible
latent image into visible form.
• Processing initiated at latent image speck.

30. Developing agents
• These are the reducing agents, which carry
out the primary function of supplying the
electrons that convert the exposed silver
halide grains to silver.
• Characteristics: 1. Selectivity 2. High activity
3. Should be resistant to bromide ions in the
solution.

31. 1.DEVELOPINGAGENTS
• Hydroquinone + phenidone/metol
• Hydroquinone(developer) +silver ions
• quinone(oxidised develper) + silver atoms +
hydrogen ions
• Phenidone(developer)+silver ions
• oxidised developer+silver atoms+hydrogen
atoms

32. Advantages of PQ developers
1. Tolerant of increase in bromine ion
concentration. 2. High selectivity and low
chemical fog. 3. Adequate activity even in low
concentrations. 4. Available in liquid concentrate
form. 5. Fast acting 6. Adequate contrast 7.
Super additive effect

33. CONSTITUENTS OF DEVELOPING
SOLUTION
• Developing Agent
• Accelerator
• Restrainers
• Preservative
• Hardener
• Solvent

34. ACCELERATOR/ACTIVATOR/BUFFERING AGENT :
• Alkaline medium for the action of PQ-
accelerates the developing process
• KCO3 or KOH
• Ideal range of pH: 9.8-11.4
RESTRAINER/Anti-foggant :
• It reduces converting unexposed AgX to Ag and
thus prevent chemical fogging.
• KBr, benzotriazole(used with PQ developer)

35. PRESERVATIVE :
• It reduces the oxidation of developing agents.
Eg: Potassium sulphite.
HARDENER :
• It controls gelatin swelling to minimize risk of
physical damage. Eg:Glutaraldehyde.

36. SEQUESTERING AGENT :
• Prevents the precipitation of insoluble mineral
salts which occur in hard water areas.
• EDTA containing compounds are used .
SOLVENT :
• Carrying medium for dissolving the developer
constituents .
• Softens the film emulsion gelatin.MC used :Tap
water.

37. • An adequate combination of both
temperature of the developing solution and
total time of development is important for
complete development.

38. FACTORS AFFECTING DEVELOPMENT
TEMPERATURE FOR DEVELOPMENT
• Optimum temperature is 20-22 oC
• Below 16 o C, action of hydroquinone ceases
• Radiograph lacks contrast and density
• Can be compensated by increasing the
developing time.
• Above 24 o C (too warm) emulsion softens.
• Chemical fog results.

39. • During development ,not all the silver halides
are reduced. Only 40% get reduced.
• The remaining silver halides greatly impair
the usefulness and permanence of the
developed radiograph and hence have to be
removed.

40. STAGE 2:FIXING
• It has four major functions
• Stop any further development.
• Makes the solution more acidic
• Remove the unexposed AgX from the emulsion.
• Convert it to soluble compounds and remove it
• Makes the image chemically stable and no
longer photosensitive
• Completes the process of hardening of emulsion
• Minimizes water absorption and reduces drying
time

41. Constituents of the fixing solution
• 1. Solvent 2. Fixing agent 3. Acid 4. Hardener
5. Buffer 6. Preservative 7. Anti-sludging agent

42. 1.SOLVENT: Water
2. FIXING AGENT :2 agents:
Cyanides :Poisonous
• Not generally used.
Thiosulfates - Sodium and Ammonium Salt
(more active) – called Hypo.
• AgBr + sodium thiosulfate :Ag thiosulfate
complex + NaBr (water soluble)

43. 3. Acid:
• Prevents dichoric fog by inhibiting developing agents.
• Provides a suitable environment for the hardening agents
in the fixer.
• Acetic acid is used usually at a pH of 4-4.5.
4. Hardener:
• Reduces drying time and prevents physical damage.
Aluminium chloride and aluminium sulfate (or Chromium
compounds) are used commonly.
5. Buffer:
• Prevents sulphurization. Neutralizes the developer . Sodium
acetate is commonly used in conjunction with acetic acid

44. • 6. Preservative:
• Retards decomposition of thiosulphates .
Sodium sulphate is commonly used.
• 7. Antisludging agent: Boric acid is commonly
used and this prevents sludging of insoluble
aluminium compounds in the hardener.

45. STAGE 3 : WASHING
• Purpose of washing is to remove fixing
solution from the surface of the film.
• If the film is not properly washed, it will show
a brown staining caused by thiosulfate (fixing
agent that remains in the emulsions).
• The process by which washing works is
diffusion. Tap Water is mainly used.

46. STAGE 4 : DRYING
• The drying medium is dry air of low humidity,
which accelerates the evaporation process
and reduces drying time.
• Film drying box: Heating element with a
circulating fan. It can dry in 15 minutes.
• Film will dry properly if hung in air for a
longer period (1+ hours).

47. • The longer the film spends in the fixer, the
longer the wash time needed.
• This is a 1:2:3 ratio of developer to fixer to
wash.

48. TYPES OF FILM PROCESSING
• AUTOMATIC :
• Unloading the film • Inserting into processor
• MANUAL :
• Unloading the film
• Loading the film onto a hanger
• Development
• Fixing
• Washing
• Drying

49. AUTOMATIC PROCESSOR
• Tanks 1. For Developer solution 2. Fixer
solution 3. Wash tank for water.
• During a 90s processing cycle, Developer-26s,
Fixer - 15s, Wash - 15s ,Drier - 24s, Travel time-
10s.

50. MANUALPROCESSING
• DEVELOPING :
• It is done by time – temperature technique .
• Here film is immersed in developer for 4 minutes.
• Temperature is maintained at 20 o C .
• At time interval within 4 minutes ,film is
examined under safelights.
• If image seems to lack expected density at 4
minutes, development is continued.

51. MANUAL PROCESSING
RINSING :
• Purpose is to slow the action of developer and to
remove it from the surfaces of the film, done by a
plain rinse bath.
• To stop the action of developer, done by acid stop
bath.
FIXING :
• After rinsing, the film is immersed in fixer
solution
• Fixing time can be up to 5 minutes

52. MANUALPROCESSING
WASHING:
• Immerse the film in large tank or in a series of
tanks through which water is kept flowing.
• Time duration:- 20 – 30 minutes
DRYING :
• Hot air drying cupboards or by rapid drier
machines.
• Temperature may vary from 40-50 C

53. 4 Steps of Processing
• Developing – formation of the image .
• Fixing – stopping of development, permanent
fixing of image on film.
• Washing – removal of residual fixer.
• Drying – blowing of warm air over film.

54. COMPARISON
• MANUAL:
• Developing temp. 20 o c
• Fixing temp. 20 o C
• Washing temp. 20 o C
• Drying temp. 43 o C
• Developing time 3-5 MIN • Fixing time 2-10MIN •
Washing time 15-30MIN • Drying time 15-20MIN
• AUTOMATIC :• 35 o C • 35 o C • 35 o C • 57 o C •
25s • 15s • 15s • 20s

55. CLEANING THE PROCESSING TANKS
• The action between the mineral salts in the
water and carbonate in the developing
solutions produces a deposit on the inside
wall of the processing tanks.
• A commercially prepared stainless steel tank
cleaner can be used to remove these deposits.
• Or simply brush thoroughly with a brush and
water.

56. Few important points to be kept in
mind
• The developing solution should be tightly
covered when not in use to reduce oxidation.
• The solution should be discarded and replaced
after three months of use because oxidation
and accumulation of gelatin sludge and other
impurities will cause poor development.
• As the solution weakens, it first turns yellow,
then brown. When it turns brown, indicating
exhaustion, it should be replaced.

57. REFERENCES
• Christensen’s physics of diagnostic radiology