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06-12-2011 |
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Black-and-White Reversal Process
Exposure. When you expose the film to light, a invisible image is formed in the photographic emulsion, called latent image. The photographic emulsion consists of silver halide crystals suspended in gelatin, coated onto substrate called film base. The substrate is a plastic film (polyester or cellulose acetate). The latent image is a small cluster of metallic-silver atoms formed in or on a silver halide crystal due to reduction of interstitial silver ions by photoelectrons.
(1) First Developer. The developer is a chemical that makes the latent image on the film visible. The developer chemically reduces the exposed silver halide in the film to form a metallic-silver image (negative image).
(2) Rinse. Removes first developer from the film.
(3) Bleach. The bleach is a chemical that dissolves the metallic-silver image (negative image) that is produced in the first developer but does not affect the remaining undeveloped silver halide.
(4) Rinse. Removes excess bleach from the film.
(5) Clearing. The clearing bath is a chemical that removes any bleach left after rinsing and prepares the residual silver salts (unexposed silver halides) for the subsequent steps.
(6) Rinse. Removes clearing from the film.
(7) Re-exposure. In this step, the silver halide crystals that were not exposed in the camera have to be exposed to light to make them fully developable.
(8) Second Developer. This developer reduces the re-exposed silver halide remaining in the emulsion to form a metallic-silver image (positive image).
(9) Rinse. Removes second developer from the film.
(10) Fixer. Redevelopment leaves a small proportion of silver halide grains undeveloped. And there may be silver salts or other hypo-soluble compounds deposited on the film, which will darken and discolor the highlights after the film has been stored and exposed to light. One of the functions of the fixing bath is to dissolve these residues, causing a reduction in minimum density and an improvement in overall brilliance and highlight quality. This step should yield minimal silver.
(11) Rinse. Removes fixer from the film.
(12) Final Wash. You use a wetting agent to aid in even drying and an antifungal agent to protect the film.
(13) Drying. Dries the film in preparation for projection.
(II) How Each Processing Solution affects Your Results.
(1) The first developer is the most critical phase of the process. Consistent results are only achieved if temperature, time, and agitation are followed. The required development time could vary with different processors and will need to be determined by practical tests. Lengthening the first development time leads to lighter films. Shorting the time will produce denser films. While some control of maximum density, minimum density, and contrast can be exercised in other steps of the process, the effect of excessive or insufficient first development cannot be fully compensated for in the later steps, and a loss of quality is almost inevitable. It is very important to choose the correct developer. There are developers of many types: high-contrast, low contrast, slow, fast, etc.
(2) A water wash is necessary to prevent the carry-over of first developer into the bleaching solution. Between the developer bath and the rinse, you can pour into the tank a stop bath (concentration of acetic acid around 1 to 2%) for 1 minute. The developer is an alkaline solution and the stop bath is an acid solution. When you pour the stop bath into the tank, the pH of the developer is altered and it stops working.
(3) Occasionally, the bleach can cause heavy density and streakiness to appear in the picture after the second developer. This may result from insufficient agitation, improper mixing, or from an increase in pH of the bleach due to use of the bleach solution beyond its capacity. Too much bleach time can result in a reduced sensitivity to re-exposure,causing a selective loss in lower mid-tone densities and consequent excessive contrast. A high level of agitation is important in the bleach. You can the bleach solution with potassium dichromate or potassium permanganate. If you use pemanganato, bath temperature should never exceed 20ºC. If this temperature is exceeded, the emulsion may be damaged. This bleach solution is less toxic and easier to remove from the film. An you need less time and water to clean the film.
(4) It is important to thoroughly wash the film thoroughly to remove the bleach solution, because otherwise, it can lead to stains.
(5) A stronger than recommended clearing bath or a long immersion time will often cause a loss in density. Short times in the clearing bath can lead to stains.
(6) You can do this rinse at the same time than the re-exposure. The re-exposure should be done with the film immersed in water. Thus the light falls evenly over the surface of the film. Drops on the film surface can cause that the light is not evenly.
(7) The re-exposure should be sufficient to render the residual silver salts fully developable. Optimum re-exposure is about 8600 Lux-sec (800 fcs). This will be provided by a 10-second exposure to a 60-watt lamp at 12 to 18 inches (31 to 46 cm). The amount of re-exposure is not critical. However, excessive exposure (in the order of 10 times) may cause a slight and undesirable increase in density, which will be most noticeable in the highlight areas of the projected image. Too little re-exposure (in the order of 1/100 of the optimum) tends to reduce the maximum density objectionably. Re-exposure levels should be checked by trial to ascertain that no noticeable change in picture quality accompanies a two- to five-times change in re-exposure in either direction. Re-exposure can be applied at any point from the latter part of the clearing treatment to the early part of the second developer. If re-exposure is given in the clearing bath, no additional contact with that bath should be required; if given while the film is in the second developer, sufficient time must be allowed subsequently for the developer to complete its work.
(8) In this step, use the same developer, but half the time that you used on the first step. You can also use two differents developers: one of low constrast and other of high contrast. For the first step you use the low contrast developer and, for the present step, you use the high contrast developer.
(9) Between the developer bath and the rinse, you can pour into the tank a stop bath (concentration of acetic acid around 1 to 2%) for 1 minute. The use of stop bath prevents contamination of the fixing bath. This is important when the fixing bath is not acid, because stains may appear in the film.
(10) An exhausted fixer, or one that contains an excess of dissolved silver halide, won’t remove all of the unexposed silver halide from the film. As a result, films will turn yellow after a time in the white areas.
(11) You can use a hypo clearing agent to shorten the rinse time. This chemical removes the fixer from the film.
(12) Use distilled water for your final rinse and wetting agent. This agent will prevent that appear water marks when the film is dry. You can also add an antifungal agent to preserve intact the gelatin if storage conditions are not right (high relative humidity).
(13) For drying, you can hang the film on a rope or you can leave it in the tank. If you hang the movie, you must be careful. The film can be damaged if the emulsion touches the rope. You can also use a drying rack. Keep the film-drying area clean and free of dust. If the film is over-dried and has excessive curl, the ambient conditions may be too dry; the temperature may be reduced or the relative humidity may be increased.
(IV) General Notes.
(a) Agitation is also an important factor for the final result. In the case of manual processing try to be consistent. If the agitation is excessive, you can increase grain of film. For similar results, you should always agitate the same way. You have to move the spiral in the sense of clockwise. Agitation for all steps: continuous the first 15" and during 5" every 30" (or 10" every 60").
(b) Maintain total darkness during first developer and first minute of the bleach solution. The next processing steps can be done outside the developing tank. When working with the tank open, light the room should be soft.
(c) You can develop the film at temperatures between 16 and 25º C. You can consult the following table to set the times to temperature, clic here.
(d) Filtration. Processing solutions and wash water may contain some insoluble materials. If these materials aren’t filtered out, they can stick to the film or to tank walls, and possibly damage the film. You must filter out chemicals and must keep the tank clean.
(e) The temperature and the processing time are critical factors in the first developer step. In the other steps, the temperature and the time are not so critical.
(V) Some formulas.
Note: To prepare processing solutions, distilled or (if not available) at least boiled water is recommende.
Bleach with Potassium Dichromate (Foma FB-2) [5 minutes at 20ºC] 1. Water.......................................................750 mL 2. Potassium Dichromate................................5.0 g 3. Sulfuric Acid (96%)..................................10.0 mL 4. Water to make..........................................1 L
Bleach with Potassium Dichromate (Orwo 833) [1-2 minutes at 23-25ºC] 1. Water.......................................................750 mL 2. Potassium Dichromate...............................10.0 g 3. Sulfuric Acid (96%)..................................15.0 mL 4. Water to make..........................................1 L
Bleach with Potassium Dichromate (Kodak Bleach R-9) [2-3 minutes at 20ºC] 1. Water.......................................................750 mL 2. Potassium Dichromate...............................9.0 g 3. Sulfuric Acid (96%)..................................12.0 mL 4. Water to make..........................................1 L
Bleach with Potassium Permanganate (Kodak Bleach R-10) [60 seconds at 20ºC] 1. Water......................................................750 mL 2. Potassium Permanganate...........................2.5 g 3. Sulfuric Acid (96%)..................................15.0 mL 4. Water to make..........................................1 L
CAUTION: Always add the sulfuric acid to the solution slowly, stirring constantly, and never add the solution to the acid; otherwise, the solution may boil and splatter the acid, causing serious burns.
Clearing Bath (Foma FB-3) [3 minutes at 20ºC] 1. Water......................................................750 mL 2. Potassium Disulfite....................................50.0 g 3. Water to make.........................................1 L
Clearing Bath (Kodak CB-2) [30 seconds at 20ºC] 1. Water......................................................750 mL 2. Sodium Sulfite (Anhydrous)......................210.0 g 3. Water to make.........................................1 L
Fixer (Calbe A 30, used by Orwo) [1 minute at 23-35ºC] 1. Water, about 50ºC...................................750 mL 2. Sodium thiosulphate 5 hydrate..................200.0 g 3. Potassium bisulphite...................................20.0 g 4. Water to make....................................... .1000 mL
Fixer (Kodak fixer F-10) [50 seconds at 20ºC] 1. Water, about 50ºC.....................................500 mL 2. Sodium thiosulphate (hypo).........................330.0 g 3. Sodium Sulfite (Anhydrous).........................7.5 g 4. Kodak Balanced Alkali...............................30 g 5. Glacial Acetic Acid.....................................19.5 mL 6. Potassium Alum..........................................22.5 g 7. Water to make....................................... .1000 mL
Sodium Metaborate is an alkali, a moderate one, that Eastman Kodak calls 'Kodalk' or 'Kodak Balanced Alkali'. Is chemically close to Borax but a bit more alkaline.
(VI) Solution storage.
In a completely filled and closed glass or PVC (plastic) container, the working solutions will keep on average of the following:
(VII) Consulted documents.
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(I)
General description of what happens during the processing steps.