Controlling Print Image Tone

30 marzo 2006  Pier-Luigi  Formule (0)
Two main factors control the color or image tone in a black-and-white print. The first is the type of paper and its halide composition, meaning how much silver bromide and silver chloride it contains. Although the terms bromide and chlorobromide are terribly unscientific and misleading they do suggest something about the general halide mix in a black-and-white paper. These days all papers contain a mix of bromide and chloride, but generally speaking, a bromide paper has less silver chloride than a chlorobromide paper. Keep in mind that its altogether possible for Brand Xs bromide paper to have more silver chloride than Brand Ys chlorobromide. Bromide papers tend to be faster and produce colder or more neutral tones. Socalled bromide papers are the mainstays of general black-and-white printing. Papers called chlorobromide by manufacturers tend to be slower and yield warmer image tones. Many people like the look of a chlorobromide print over a colder, bromide type. These slower papers are also more flexible in that they respond more readily to image tone manipulations produced by developer modifications. Chlorobromide are best suited for neutral to cool print tones. Amidol is considered as the classic developing agent for creating cold tones on bromide papers. Cooler color is best obtained with print toners. Neutral and cold tones tend to create an emotional distance, a sense of looking at the image from the outside. Warm tones tend to engage the viewer emotionally, drawing them to the image. Learning to manipulate and control the tone of a print opens up new vistas and ways to communicate a photographer vision. Whereas the tint is most easily seen in the highlights, the tone of a print is most obvious in the shadows. The developer is the second factor contributing to image tone. A developer can foster either a warmer or colder tone depending on its composition. Although developer composition exerts an enormous influence on overall image tone, it turns out that most image tone effects can be controlled with just three ingredients; bromide concentration, organic restrainer (antifoggant), and type of developing (reducing) agent. Cold tone developers can be used to produce very subtle cool tones on bromide papers. Gold toning of normally warm chlorobromide papers is generally reconized to provide the most pleasing cool image tone. Paper-Developing Agents Pyrocatchin: warm tones. Glycin: neutral tones and subtle gradations. Amidol: cold-tone formulas. Manipulating The Print Image Tone Cold Tones MQ Developers Reduce the amount of bromide. Reduce the amount of bromide and add benzotriazole. PQ Developers Eliminate the bromide and replace it with 1 benzotriazole solution. Increase the benzotriazole, 1 solution, up to 15 ml per liter of working solution. Substitute Phenidone and benzotriazole for metol and bromide. Neutral Tones Eliminate or reduce the amount of bromide and/or substitute benzotriazole. Warm Tones Reduce the amount of sodium carbonate. Substitute potassium carbonate for sodium carbonate. Increase the amount of potassium bromide using a 10 solution. Increase the exposure and shorten the developing time. Dilute fresh developer with up to 50 used developer. Generally speaking, increasing the bromide level in a developer leads to warmer tones, whereas increasing the level of an organic antifoggant (e.g. benzotriazole) leads to colder tones. Since PQ (phenidone -hydroquinone) developers generally contain an antifoggant, they often produce colder tones than nominally equivalent MQ (metol -hydroquinone) types. Developers containing the agents glycin or chlorohydroquinone produce warmer tones if organic restainers are ommited from the formulation. These agents produce more neutral tones if an organic restrainer is included. This suggests that you could devise a continuous-tone control scheme using a stock, warm-tone glycin or chlorohydroquinone developer plus a stock solution of benzotriazole, or 6-nitrobenzimidiazole, etc. The system would be calibrated for a particular print paper by adding varying drops of restainer to produce a given image tone. Potassium bromide may be added as a restrainer. It should usually be prepared as a 10 percent solution. You might begin with about 50ml of a 10 solution of potassium bromide per liter of stock developer. Check on the effect of the bromide, and add more as necessary until you have the disired effect. Examine the print in daylight if feasible, for a more accurate color evaluation. The bromide sometimes adds a slightly greenish tone to the image, which can be overcome in most cases by selenium toning. Benzotriazole (Kodak Anti-Fog #1) provides about the same restraining effect, but produces a noticeable shift in print color toward the blue. Use 25ml of a 1 solution of benzotriazole per liter of stock developer. Adding 50 ml of the 1 solution causes a noticeable color shift toward the blue, and with 100ml the effective paper speed by roughly two-thirds of a stop. Increased amounts of benzotriazole seem to affect the image contrast somewhat, more so than potassium bromide, but this effect may depend on the paper and developer used. The use of both of these chemicals effectively reduces the speed of the papers, and thus requires an increase in exposure. They may also lengthen the emergence time of the image in the developer., and some papers may therefor require lower than normal development factors. With contemporary papers benzotriazole will cause a distinct cooling of the image color, and potassium bromide will increase its warmth. Based on the solubilities of the silver salts 1.0g/liter of Potassium bromide is roughly equivalant to 0.2g/liter of Benzotriazole (Anti-Fog#1).

 

Useful 10 solutions Sodium carbonate: To cool the image tone add 400 ml per liter of working developer. Too much sodium carbonate will fog the print. Hydroquinone: To increase the print contrast add 100 ml per liter of working developer. If you plan to store this solution, mix it with 40 grams of sodium sulfite to prevent spoilage. Metol: To reduce print contrast add 50 ml per liter of working developer. Useful 0.2 solution Phenidone: Due to the small amount of Phenidone required by many formulas, it is often disirable to use a percent solution. 100 ml of this solution contains 0.2 grams of Phenidone. Phenidone, 0.2 solution Chemical Amount Units Water (125°F/52°C) 750 ml Sodium bisulfite 90 g Phenidone 150 g Water to make 1000 ml Development Time A 3 minute standard developing time is recommended for fiber-based papers. A useful technique is to slightly underexpose the print and then extend development time about ½ again more than normally used. Oriental VC: Toning charecteristics: Medium brown thio-carbonate tone. Print Developer Formulas --------------------------\ Developer Chemical \-------------------------- B&J 1:2 GAF-125 1:2 PD-130a 1:3 Agfa-120 1:3 E-72 1:3 GD-67 1:4 D-155 1:2 WW-1 1:3 PD 106 1:3 GAF 120 1:2 Metol ($0.08/g) 3 3 2.2 - - 4 0.4 5 - 12.3 Phenidone (g) - - - - 0.3 - - - - - Glycin (g) - - 11 - - - 2.6 5 28 - Hydroquinone (g) 12 12 10 24 - - 4.0 10 9 - Ascorbic Acid (g) - - - - 19 - - - - - Sodium Sulfite (anhy) (g) 40 44 60 60 45 57 22 50 85 36 Sodium Carbonate (anhy) ($0.01/g) 62 65 67 67 82 82 18 72 153 32 Potassium Bromide (g) 0.8 2 5.5 - - 0.6 4 10 4 1.8 Benzotriazole ($0.16/g) - - - - - - - - - - Water to make (ml) 1000 1000 1000 1000 1000 1000 1000 1000 1000 1000

 

 

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