[rollei_list] Re: Developer 130
----- Original Message ----- From: "X.TRUONG" <truongthx@xxxxxxx> 
To: <rollei_list@xxxxxxxxxxxxx>
Sent: Thursday, October 30, 2008 2:40 AM
Subject: [rollei_list] Re: Developer 130



Thank you very much Mr. Knoppow.
My mail server had some problems
I saw some thing about the chemistry, metol make the print sofer, hydroquinone make more contrast, borax make film harder, postassium bromide prevent the highlight of first print??? Or sodium sunfit make the film or 
print clearly... Please give me something about these...

Best regards,
Xuan Truong
Well, the chemistry of developers is rather more complicated than this. I am not sure what books I can direct you to since the better ones are pretty old now. The understanding of photographic chemistry has changed a lot in the last twenty years so, to a real chemist, the older books are pretty outdated. Still, they give a good idea of the function of the various parts of the developer at a more elementary level. The relative contrast given by Metol or hydroquinone is partly due to the pH of the solutions they need to work. Generally, the more alkaline developers tend toward higher contrast. Metol will work in a neutral, or even slightly acid solution while hydroquinone needs a quite alkaline one. But, there is more: these two developers tend to react with each other when used in combination in a way that does not necessarily affect contrast but does affect the capacity of the developer and other characteristics because they tend to regenerate each other. The same is true of some other combinations such as Phenidone and hydroquinone and either Metol or Phenidone with ascorbic acid. A combination developer can be made to have a wide range of contrast, for instance D-76, a low contrast film developer and Dektol, a relatively high contrast paper developer, are both Metol and hydroquinone types. Borax is a relatively low pH alkali used mainly in film developers. AFAIK it was first used in Kodak D-76. D-76 is a relatively low contrast developer with fairly fine grain and good film speed. While it was originally designed for fine grain motion picture use it has become as close to a universal film developer as there is. More contrasty or more active developers usually rely on an alkali with high pH than Borax, for instance, the alkali in Dektol is sodium carbonate. In really high contrast developers, like Kodak D-8 one finds sodium hydroxide. This developer is intended for copy negatives of line work (drawings) with little, if any, gray scale. Its also a Metol and hydroquinone type. Potassium bromide is a fog suppressor also called a restrainer. Restrainers tend to reduce the number of _unexposed_ silver halide crystals that develop along with the image. If much bromide is used some of the low exposure image crystals will also be suppressed. Film developers tend to have the minimum amount of bromide necessary to eliminate fog and some developers, D-76 for instance, usually do not contain bromide. This is because bromide tends to reduce the usable film speed. Print developers have more because fog in a print veils the highlights and is very undesirable. Bromide comes out of film when its developed and accumulates in the developer. It tends to reduce fogging but also reduces the film speed especialy in the shadows. Some developers are more affected by bromide than others. For instance, Metol is relatively unaffected while hydroquinone is strongly affected so one finds lots of bromide in very high contrast developers which use bromide. There are more modern fog suppressors which have less effect on film speed. The one most often encountered is benzotriazole which is often found in developers using Phenidone. Sulfite has a very complex function in a developer. It tends to absorb oxygen preferentially to the developing agents so protects them from oxidation from contact with the air. It also has anti-oxident action with the reaction products of development. These last are complex and vary with the developer. For instance, the reaction products of Metol tend to suppress development while those of hydroquione tend to accelerate it. Where both developers are used these two properties tend to counteract each other and sulfite reduces them even more. Sulfite also has a "salt effect" which tendst to prevent swelling of the gelatin. This is important for several reasons but one important one is that it tends to prevent the migration of individual developed silver grains causing "grain clumping" and a grainy appearance. Sulite has another very important function and that is as a silver halide solvent. The solvent effect affects the way the silver crystals form when developed and tends to minimise grain. At the level of solvent action present in developers like D-76 the action also tends to slightly dissolve the surface of the halide crystals making more development centers available to the developer and increasing film speed slightly. More solvent action, for instance as in full strength Microdol-X, will destroy some of these development centers thus losing some speed. There is an optimum amount of sulfite which depends on the rest of the chemistry and on the intended use of the developer. Sulfite is also present in fixing baths to prevent oxidation of the thiosulfate and also to prevent staining from carried over developer. Liquid concentrate developers often do not have sulfite but rather some other chemical which can be dissolved in sufficient concentration but which functions as sulfite in the active developer. These four functions: developing agent, preservative, accelerator, restrainer, are present in nearly all developers. In a few cases sulfite is used as both the preservative and accelerator (D-23) and the preservative and restrainer are not always sulfite and bromide, as pointed out above, and not all developers have a restrainer (D-76, D-23 and others) but these four functions are present in nearly all. 

--
Richard Knoppow
Los Angeles, CA, USA
dickburk@xxxxxxxxxxxxx 
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