When exposing films from which prints are to be ultimately made, exposure is not critical as any variation in negative density can usually be compensated for at the printing stage. When a film is to be reversal processed camera exposure must be fairly accurate if good quality transparencies are to be produced. For general outdoor or indoor work an exposure meter should be used and the published meter setting for the film used as a guide to exposure - though the setting that will give the best results for any one user may be slightly different and is best determined by a practical test.

Exposures for copying can be determined by taking an "artificial highlight" meter reading. To do this a sheet of clean white paper - approximately 12 inches square - should be placed over the evenly illuminated original. Hold the meter about 6 inches away, facing the white paper, and note the maximum reading obtained as the meter is slowly moved from side to side. The recommended setting for Pan F when using a Weston meter by this method, and using the "O" position on the exposure dial, is 25.

When copying, the exact exposure for a particular set of conditions should ultimately be found by trial and error even is an exposure meter is used. It is a good idea to make a series of trial exposures at half, equal and double the indicated exposure. Examine the processed result - over-exposure gives too light a slide, under-exposure too dark a slide.

Recommended Safelight

The recommended safelight for use with Ilford B&W films is an Ilford GB safelight Nº 908 (very dark green). In practice, it is safest to process the film in total darkness.

Solutions Required

Reversal developer

Ilford Bromophen developer made up to contact paper strength and with the addition of sodium thiosulphate (hypo) crystals, as given below, is recommended for the reversal processing of Ilford films.

Pan F, FP3 roll-film, Selochrome, HP3 and HP4 films: 8 grams hypo/litre; FP3 35mm and FP4 film: 12 grams hypo/litre.

Bleaching Solution

Sol A.
Potassium Permanganate 2 g
Water to 500 cc

Sol B.
Sulphuric acid conc. 10 cc
Water to 500 cc

Note: Always add the acid to the water slowly whilst stirring. It is hazardous to add the water to the acid.

The stock solutions will keep for a long time. For use mix equal parts of A & B. Mix a fresh working solution for each film.

Clearing Solution

Sodium (or Potassium) Metabisulphite 25 g
Water to 1 litre

Fixing Bath

A hardening fixing bath should be used, as the bleaching operation softens the emulsion. The use of Ilford Hypam Fixer - with hardener - is recommended.

Processing

In the method of reversal processing described in this sheet, a negative image is first obtained by development of the original latent image. This negative image is then dissolved away in a bleach bath, and the silver halide remaining is exposed and developed, giving a positive image. The second development is followed by fixing in an acid hardening fixing bath. The time required to carry out all the operations from the first exposure to the beginning of the final wash is about 30 minutes.

First Development

An ordinary spiral tank is recommended for the first development. Fill the tank with the recommended quantity of developer, and adjust the temperature of the developer to 20ºC. Place the tank in a water-bath to maintain a constant temperature. Working in total darkness, load the exposed film into the spiral and lower this into the developer, lifting it out again to remove air-bells before placing the cover on the tank. Agitate during development by giving a 5 seconds inversion to the tank every 15 seconds.

A development time of 12 minutes at 20ºC is recommended for all the Ilford films listed. It is important that this time and temperature be closely adhered to if consistent results are to be obtained. Careful control of the time and temperature of the first development is as important as accurate camera exposure. It is best to remove the cover from the tank before development is complete so that the spiral can be quickly removed from the developer and immersed into water to rapidly stop development. The developer, which will be required later for the second development, should be kept until needed. The tank itself must be washed and should then be filled with the bleaching solution (mixed at working strength) in readiness for the bleaching operation.

First Washing

Wash for 3 minutes in running water.

Bleaching

Treat the film for 5 minutes in the bleaching solution at 20ºC with continuous, strong agitation, lifting the spiral from the solution and returning it rapidly and repeatedly. This vigourous agitation is necessary to ensure complete bleaching. White light may be switched on after the film has been in the bleaching solution for 30 seconds. The rest of the process can be carried out in white light.

Second Washing

Wash for 2 minutes in running water.

Clearing

Soak the film for 2 minutes in the clearing solution.

Third Washing

Wash for 2 minutes in running water.

Second exposure

Remove the film from the spiral and expose it for the equivalent of 30 seconds at 18 inches from a 100-watt tungsten-filament lamp. Insufficient second exposure will result in a reduction in density when the film is finally fixed. Two to four times the specified exposure may safely be given, but over exposure beyond this extent may lead to foggy highlights.

(An alternative if the spiral is clear, is to leave the film in it and immerse it in a white bowl of water at 20ºC, then illuminate from above, moving the bowl or the lamp slowly to even out the exposure to all parts of the film. Give a longer exposure, two to four minutes or more. Barry)

(Take care not to allow any splashes of water to get on the lamp, they may cause it to shatter, sending glass flying and exposing the live parts inside. Also, do not handle the light fitting, wires, plug or other electrical parts, or touch the switch, with wet hands. Barry)

Second Development

If the spiral tank employed permits re-insertion of the film in the spiral this should now be done. It may help if this operation is carried out under water. If, however, re-insertion of the film is not possible, the second development and subsequent operations may be carried out in a dish by the "see-saw" method.

Develop for 6 minutes at 20ºC in the solution used for the first development - the hypo in this developer helping to give clear highlights. Development time is not critical - it should simply be continued until maximum density is achieved.

Fixation

Fix for 10 minutes in the acid hardening fixing bath.

Fourth Washing

Wash in running water for 30 minutes.

The film is ready for projection when dry.