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PLATE PROCESSING AND COPYING

Procedure for development of 10 x 10 and 5 x 7 inch plates using tray rocker development in the 5th floor darkroom

Preliminary Check List
This is a step by step outline. More detail is given in the Notes.

1
Pour an accurately measured 2 litres of developer into the grey PVC rocker tray and replace the lid. (Note 1).
Ensure that the temperature of the solution is 20°C ±0.5°C. (Note 2).
2
Ensure sufficient developer is available for the anticipated night's work. (Note 8).
3
Mix 8 litres of de-ionised water and 80mL Kodak Indicator Stop Bath in the large white tray alongside the tray rocker. This gives a solution containing 0.85% v/v acetic acid. (Note 3).
4
Check that the two gas burst fixer tanks are filled to the indicated mark and are levelled in the sink. (Note 4).
5
Set the nitrogen pressure regulator to deliver 100kPa and check that all tubing is free from leaks and kinks. (Note 5).
6
Set the nitrogen burst control unit to deliver a 1.2 second burst every 8 seconds and run the system briefly to clear the pipe work. (Note 6).
7
Ensure that the rinse and Hypo-Clear baths are filled.
8
Place a grey PVC processing rack in the sink between the stop bath tray and firstfix. Separate racks are available for 10 x 10 and 5 x 7 inch plates.
9
Close the outer darkroom door and close and lock the inner door. An illuminated `IN USE' sign is activated by the lock. (Note 7).

Development Procedure. (Note 8)

1
Insert the plate, emulsion up, in the clear Perspex frame and push in the retaining clips. (Note 9).
2
Start the tray rocker (foot switch) and remove the lid.
3
Push the Perspex frame firmly but without splashing into the developer, start the timer and replace the lid. (Note 10).
4
Towards the end of the development time, remove the lid and locate the lifting handles on the tray. Lift the tray clear of the rocker and allow to drain for a few seconds, with the tray vertical, one corner down.

5
The end of the development time should coincide with entry of the plate into the stop bath. Push the tray firmly into the solution. Do not slide the tray in. Lift out first one side, then the other, repeating this rocking action several times fairly quickly. (Note 11).
6
With the processing frame still immersed in the stop bath, withdraw the holding clips and transfer the plate to the grey PVC processing rack. Note that the emulsion is very tender at this stage. The plate can remain in the stop bath as long as necessary i.e. long enough to put the next plate into the developer.
7
Lower the rack into the first fix bath and turn on the gas burst control unit. The first burst occurs 8 seconds later. Fix for 2 or 4 minutes. (See Note 15 for a description of the gas burst controller.)
8
Transfer the rack to the second fix bath. Fix for a further 2 or 4 minutes. (Notes 12, 13).
9
Transfer to the running water rinse bath. The time is not critical, but a minimum of one minute with occasional agitation of the rack is suggested.
10
If necessary, remove remaining traces of antihalation backing with a cotton wool pad wet with developer. 098 and IIIaF plates have particularly tenacious backing and backed IV-N plates need special treatment. (Note 14).
11
Immerse in Hypo-Clearing solution for at least two minutes and use gas burst agitation as for the fixer.
12
Wash in running water for at least 10 minutes, and then rinse briefly in PhotoFlo 600. (20mL concentrate in 13 litres (3 imperial gallons) of water.
13
Gently swab the emulsion with a cotton wool pad provided and rinse off any particles with a brief flood of distilled water.
14
Dry in wooden rack, corner down in room air. Do not force dry.

Developing 2 2 inch plates using nitrogen burst development

Preliminary Check List]

1
Check that the half-gallon tanks of developer and fixer are connected to the nitrogen lines from the gas burst control unit, A separate line is used for each solution. (Note 15).
2
Set the gas burst controls to deliver 1.2 second bursts every 8 seconds.
3
Set the nitrogen pressure to 50 kPa and check for leaks and kinks.
4
Check the distribution pattern of bubbles, particularly in the developer tank. If necessary level the tank by packing card or old plates beneath it.
5
Check solution temperatures. (Note 16).

Development procedure (Note 17).

6
Load the plates into the special nylon inserts in the racks provided. (Note 18).
7
Remove the floating lid from the developer, switch the gas burst control on and insert the rack of plates. (Note 19).
8
Towards the end of the development time, lift the rack clear of the tank and allow 10 seconds draining.
9
Immerse the rack in the stop bath. This should be regarded as the termination of development time. Re-immerse and drain several times over a 30 second period.
10
Fixation and subsequent operations are essentially similar to those described in section 6.2.7. - 6.2.12. A wooden rack is provided for drying. Small plates can be dried in the drying cabinet in moving cold air without ill effect.

Notes
1
The quantity of developer is critical. The angle of tilt and tocking rate has been adjusted to give maximum uniformity with 2.0 litres of solution in the tray. (See Miller 1971)
2
The developer temperature must remain constant for plate to plate consistency. The recommended temperature is 20°C. The room temperature is set so that this temperature is maintained in the tray rocker with the lid on. An immersion heater is provided to raise the temperature of solutions which have cooled through evaporation. The 1500W heater will raise 2 litres of solution through 1°C in about 7 seconds. The element must be totally immersed and not in contact with plastic.

The temperature of other solutions and washes is less critical and should be in the range 18 to 21°C. Sudden temperature changes from bath to bath cause reticulation of the emulsion and must be avoided.

3
The 10 mL Kodak Indicator Stop bath per litre of water is a lower concentration than that recommended by Kodak for graphic arts films and plates. However, experience has shown that the normal 16 mL per litre (equivalent to 1.3% v/v acetic acid) can cause bubble formation in the emulsion.
4
For even gas distribution the tanks must be level. Two metal shims are normally left beneath the tanks to compensate for the slope of the sink.
5
Leaks in the tubing will allow gradual flow-back of solution into the distributor and lines. A significant and variable fraction of the burst time will then be taken up clearing the system, thus reducing agitation efficiency.
6
Burst times much over 1.2 seconds allow the bubbles to form flow channels in the liquid giving uneven agitation across the plate. Although the fixation process is taken to completion it seems sensible to allow it to do so in controlled manner. There is nothing to be gained by increasing the burst time beyond 1.2 seconds. The 8 second interval is the minimum available period between bursts.
7
The outer door of the 5th floor darkroom is not completely light-tight, the inner one is. The amount of light entering the darkroom with the inner door open and outer door closed is very small. With the lid on the tray rocker it is possible to leave the darkroom during long development cycles without endangering the plate, which is in any case relatively insensitive once in the developer. The gas burst fixer tanks are also sufficiently light-tight with the lid in place to permit exit from the darkroom during processing. Make sure you stick a notice on the outer door if you leave a process under way. Make sure you remove it when not required.
8
Kodak publication J1 (Kodak 1973b, page 24) indicates that 2 litres of D19 will process the equivalent of twenty 10 x 10 inch plates and 2 litres of D76 will process eight such plates before the solution is exhausted. For very critical work where plate to plate consistency is essential the developer may be replaced after every 10 x 10 inch plate or every pair of 5 x 7's. If this kind of precision is required the developer temperature must also be reproduced and maintained to ± 0.05°C for each plate.

Normally 2 litres of D19 will process the equivalent of five 10 x 10's plates without noticeable loss of activity and D76 will process two plates.

Loss of developer activity also occurs through aerial oxidation. Replace the developer in the tray rocker at least once in the night irrespective of the number of plates processed.

9
The frame must be clean and dry and at room temperature when the plates are loaded. This can be done while the previous plate is still in the developer. When developing 5 x 7 inch plates both spaces in the frame must be occupied. Cleaned 5 x 7's plates are available to fill the vacant space when processing single plates.
10
The plate must be wet rapidly and evenly and all developer displaced from beneath the frame to assure even processing, but this must be achieved without splashing. It is normal for the frame to move ± 1mm withint the PVC tray during the rocking cycle. Replacing the lid minimises evaporative cooling.
11
The time in the stop bath is not critical, but must exceed 30 seconds. Efficient and even termination of development is as important as the initial wetting stage in the developer. Use vigorous agitation for the first half minute in the stop bath.
12
As from June, 1985 (plate 2397) we have abandoned the use of `conventional' fixer in favour of Kodak Rapid Fixer (Liquid) with hardener, in an attempt to improve archival storage properties. A two-bath system is used, with the fixer diluted 1 vol concentrate + 3 vol water in each. Hardener is added according to the manufacturer's recommendations.
13
A useful rule of thumb is to fix for twice the clearing time. At 20°C the clearing time of fine grain emulsions is 1-1.5 minutes while some coarse-grained emulsions take up to 3 minutes to clear.
For fine-grain emulsion types IIIa, IV, 2415 etc. - Fix for 2 minutes in each bath
For coarse-grain types IIa, 098, 103a etc. - Fix for 4 minutes in each bath
The plates may be inspected in white light after the first fix bath. However they should be immersed in the second fixer to complete the removal of soluble silver and thiosulphate complexes for a period similar to the clearing time. This and subsequent processes may be carried out in white light.
14
The removal of any remaining backing almost certainly will be carried out in white light. If the plate is handled for inspection at this state it is probably more convenient to rinse it under the tap. The rinse is important to avoid excessive carry-over of fixer and to maintain the activity of the Hypo-Clear.

IMPORTANT The fluorescent X-ray viewers mounted on the wall and in the bench top have a bright and persistent afterglow. This is normally not seen because the fluorescent light destroys dark adapted vision very quickly. Do not use the bench mounted viewer until processing is completed. The afterglow takes several minutes to disappear completely.

15
The small tanks are conveniently arranged on the flat part of the bench between the sinks. The tanks should be level on that surface but must be checked before use. The Kodak gas burst distributor is fitted with two (non-standard) toggle switches, one for each solenoid valve. The two valves can thus be operated independently, both in the continuous mode (switch up) to clear the pipe work and via the timing circuits (switch down) for normal operation. In the central position the timer still operates but does not actuate the solenoids. Turn the unit OFF with the central rotary switch.
16
Gas burst agitation for 15 minutes as recommended in section 6.3.2 lowers the temperature by about 1°C. For critical work with a 15 minute development time it is suggested that the `drift-by' method be used, i.e. start development at 20.5°C and assume a constant fall to 19.5°C over 15 minutes. The temperature of other solutions should be in the 18-21°C range.
17
Each tank holds about 1700mL of solution. D19 should process at least 100 plates 2 x 2 inch plates without noticeable loss of activity. D76 should be discarded after processing 40 plates. The life of the developer is considerably extended by use of the floating lids provided. These also serve to minimise evaporative cooling.
18
There must always be at least two plates in the rack. Whatever the number, the end members must always be turned emulsion in so that there remains a constant space between emulsion and either another emulsion or plate back. Do not leave spaces in the centre of a partially filled rack.
19
The rack is designed to sit on the gas burst distributor at the bottom of the tank. The long direction of the rack must be parallel with the long direction of the tank and the rack must be reasonably central within the tank. In all other solutions the rack can be at 90° to the above position, i.e. the handles resting on the tank sides.

Plate Copying

It is our policy to copy all direct plates (at least to the stage of a positive film) before they leave the Observatory. These copies will not be used or made available to others without the written permission of the original investigator for at least 2 years (longer by negotiation with the Director) from the date of exposure of the original plate. The process for making these copies may be of general interest and is outlined below.

The Film

Kodak Commercial Film type 4127 is available in 4 x 5, 8 x 10 and 10 x 12 inch sizes. This material is blue sensitive, has fine grain and an excellent straight line characteristic curve when processed as described below. The film can be handled under bright red safelight conditions (Kodak safelight filter 1A, 25 Watt lamp no nearer than 1.5m from the film). The film edge is notched so that the emulsion faces you when the notch is at upper right.

The Developer

Extensive experimentation has shown that this film will maintain a linear characteristic curve at low (0.60) over a brightness range of 1000 to 1. To achieve this the exposed material is processed in 2.5% Ilford Print developer (Ilfospeed) or Kodak Dektol liquid at the same concentration for 3.5 minutes at 20°C.

The Contact Printer

Copies are made by exposing the film in contact with the plate in the Agfa-Gevaert SV400 diffuse light vacuum contact printer. This tungsten light printer has been modified to give 12 brightness levels, each step about twice as bright as the previous one. The steps are selected by means of a six-position step switch and two-position toggle switch. Brightness increases from A1 to A6, and from B6 to B1.

The unit has been calibrated using the 4127 film and 2.5% Ilfospeed developer, and calibration curves are kept with the instrument. The unit is run via a constant voltage transformer for consistent results. Calibration and exposure information is with the printer in the first floor dark room.

Determination of Exposure

To retain information about the faintest objects and at the same time preserve as much detail as possible in the denser parts of a plate, the exposure for the film copy is chosen to produce a background (sky) density of 1 to 1.2 (ANSI diffuse, as measured on the Macbeth densitometer) irrespective of the fog level of the original plate. The density of the sky background towards the centre of the plate is measured on the Macbeth and simply read off on the calibration curve. This curve is drawn for a standard time of 10 seconds exposure.

Procedure

1
Measure the lowest background density towards the centre of the plate using the Macbeth densitometer.
2
Read the appropriate exposure from the calibration curve. Pre-set the timer (rotate the clear cover) and the step and toggle switch.
3
Place the plate emulsion up on the platen of the printer and clean with a soft brush. Place a sheet of film emulsion down on the plate.
4
Close the printer lid. The vacuum pump should start. Press on the lid to establish a vacuum seal. When the vacuum gauge reads 0.6 kp/cm, wait 30 seconds, then start the exposure by pressing the centre of the timer firmly.
5
At the end of the exposure, press the small button behind the timer to release the vacuum and lift the lid.
6
For 8 x 10 and 10 x 12 inch film, mix 25mL of Ilfospeed developer concentrate with 1000mL of water at 20°C. Ensure thorough mixing and pour into an 11 x 13 inch dish immediately before use. Use once only.
7
Lower the exposed film into the developer rapidly. emulsion down. Lift and turn over and return to the developer. Lift out and turn over continuously throughout the development period, using alternate or random long and short sides of the film to grip between the fingers.
8
Stop development in Kodak Indicator Stop Bath, diluted 16 mL/litre, for about 30 seconds with continuous agitation.
9
Fix for twice the clearing time (total 2-3 min ) in rapid fixer, plus hardener diluted 1 + 5.
10
Wash for 20 minutes or rinse for 2 minutes, followed by 2 minutes Hypo-Clear and 5 minutes water wash. Rinse in diluted PhotoFlo solution and dry.

Ownership of Plates and Copies; Plate Log

All plates taken on the AAT remain the property of the AAT Board and are loaned to the investigator for two years from the date of the exposure. After that period plates must be returned to the Epping Laboratory where they are made generally available. Plates returned before the two-year period are deemed to be available for general use. The duration of the loan can only be extended by application to the Director. These conditions apply to all plates and films obtained on the telescope.

Full details of exposures are recorded in a working log by the night assistant. A computer printout of most of the information in the log is available on request with the data sorted into both plate number and right ascension (1950) order.



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Next: PHOTOGRAPHIC FACTSFIGURES Up: AAT Photography Previous: WORKING NOTES FOR



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