Benzotriazole vs. Potassium Bromide
I am trying to compound a developer which has slightly more contrast and slightly less density than the modified AGFA-Ansco 17M I have mixed. I mixed it with 5x the normal amount of sodium metaborate, as recommended in the old Ansco literature I have, to increase both the contrast and density. I would like a bit more contrast, and a bit less density. The info I have from Troop's "The Darkroom Cookbook," page 105, indicates to effect that change I should increase both the amount of hydroquinone and the restrainer, potassium bromide (KBr).
I am wondering if, instead of the KBr, I could try benzotriazole. I have mixed a 0.2% solution, for use with paper, and if anyone could advise me on how much to start with, I'll give it a whirl. My fallback position is to increase the hydroquinone to 4.0g/l, from 3.0g/l, and to double the KBr to 1.0g/l, from 0.5g/l. Any input would be appreciated!
The bromide will help the contrast. Benzotraizole is usually only added to Phenidone type developers to give colder tones. Try cutting the carbonate & raising the sulphite as well.
I thought Benzotriazol was added to print developers to keep highlights clean. At least that's what I remember from Fred Picker.
With Phenidone based developers, I add Benzotriazole when I want Blue/Black tones.
Originally Posted by George Collier
I keep percentage solutions of both KBr and Benzotriazole handy when I'm printing. Dilution, sulfite and alkali are also "knobs" that can be used.
Everything is analog - even digital :D
Benz and bromide work differently.
Originally Posted by George Collier
Benz gets rid of paper fog - where silver has already started to form in the emulsion before it has started to develop. Benz forms a waterproof polymer when it contacts any metal and this keeps the developer from acting on the grain. Once the the developer starts acting the benz has less effect. The major use of benz is rustproofing. It only works on paper that is fogging because of storage, it won't help with paper that has been fogged by light. It will change the image tone to cold as there will be fewer very small grains of silver in the resulting print as the benz has kept them from the developer action.
I find benz won't completely recover age-fogged paper, but a few seconds in Farmer's Reducer will get the paper back to white before anything happens to the highlights.
Bromide restrains the developer so that a lightly exposed grain takes longer to develop. It will keep the highlights clear but won't do as much for already age fogged paper. It will help with light-fogged paper. It will change the image tone to warm as, with the lessened developer activity, the developed silver grains will be finer.
Finer silver grains are why very dilute developers will form a warm-tone image.
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Here is a quote from a patent reference:
"On the other hand, although triazoles such as benzotriazole and imidazoles are used for preventing eluation of non-ferrous metals such as copper and copper alloys, and cobalt ions of super-hard alloys, these compounds are also unsatisfactory in respect to rustproofing abilities. "
Benzotriazole does not work in all cases as a corrosion inhibitor and rustproofing agent, and with silver halide the reaction is totally different and also sometimes failes with respect to being an antifoggant.
Benzotriazole, phenyl mercapto tetrazole and nitro-benzimidazole nitrate are all classed as antifoggants in photo engineering usage. They adsorb to the crystal surface and form mild to strong salt like materials or complexes with the silver halide to reduce development rate and fog formation. These complexes are much less soluable than the original silver halide itself. While doing so, they also 'tone' the image changing the color of the silver metal by changing the form taken by developing silver metal.
Bromide is one of the constituents of a grain in many cases and retards development simply by changing solubility of silver halide or by a counter ion effect. Development produces halide. If you add enough of the halide to the developer to start with, development slows down. Fog slows down, speed slows down and contrast lowers. Of course, this is often the same result as the antifoggants I list, but by a slightly different method. It also requires different amounts of each of these to get to approximately the same point.
Benzotriazole works with all developers as an antifog agent. As mentioned above, it helps with development fog and fog caused by aging. It tends to cool print tones very slightly. It is said to increase contrast a bit, but I have not seen this. Potassium bromide is a less effective antifog agent, but it still has that effect. It tends to warm tones a bit, depending a lot on the paper and the developer it is used in.
Wouldn't it be easier to decrease your exposure to give you less density and increase your dev time to increase contrast? Just a guess.
Originally Posted by Photo Engineer
Thanks for this very lucid and complete explanation. It is very helpful and interesting.
[QUOTE=analogfotog;621050]I am trying to compound a developer which has slightly more contrast and slightly less density than the modified AGFA-Ansco 17M
It seems to me you are creating a problem then looking for a solution. Instead of Ansco 17m, just use D76. Would not the additional hydroquinone in D76--compared to Ansco 17m-- do exactly what you want?-Moreover, the old lab rats with whom I worked back in the 1960s would sometimes increas the borax concentration of D-76--even substituting Kodalk, sometimes.
John, Mount Vernon, Virginia USA