[pure-silver] Re: Grain Size


----- Original Message ----- From: "Koch, Gerald" <gkoch02@xxxxxxxxxx>
To: <pure-silver@xxxxxxxxxxxxx>
Sent: Friday, October 27, 2006 6:09 AM
Subject: [pure-silver] Re: Grain Size


Hi Bogdan,

One could do that, but the reason that people usually use D-76 diluted is for the type of negative it then produces. The maximum action of sulfite is around 7.5% and not the 10% that is used in such developers as D-76 and D-23. So you would have to calculate the actual concentration for the added sulfite solution based on the dilution that you intend to use. The actual increase in graininess is not that much. You are not going to see boulder size grains using diluted D-76. In any case Xtol is a better choice for finer grain than D-76.

Jerry

The optimum sulfite concentration for developers of the D-76 type is around 75 to 80 grams per liter, in agreement with your 7.5%. There are other factors affecting grain such as pH and general activity. I am not a good enough chemist to explain the details. At various times there have been alternative D-76 type formulas with different concentrations of the developing agents. Some of these were designed for automatic motion picture processing machines which operate at elevated temperatures. Kodak has a formula, D-96 I think, which is an example of a modified D-76 type intended for motion picture processing. The formula is included in the "module" for B&W motion picture processing available off the Kodak web site (with some detective work to find it).
D-76 has come to refer to a family of developers of similar formulation, i.e., using Borax as the accelerator and having a high sulfite content. There are a great number of variations on this theme incuding developers with other developing agents, for instance Ilford Microphen which uses Phenidone rather than Metol. All have similar characteristics, notably relatively fine grain, near maximum film speed, fairly long development time, and reasonable acutance effects. For finest grain developers of the Microdol-X or D-25 type are optimum but both loose some film speed and do not produce the sort of edge/border effects needed for acutance. D-76 type developers employing Phenidone or one of its derivatives tend to produce maximum film speed. Maximizing acutance effects requires so called local exhaustion, really a misnomer, generally achieved by high dilution and minimum amounts of Sulfite or other protective agents. In general, high acutance developers are not compatible with minimum grain.
I have not experimented with making up D-76 with half the amount of developing agents in it but that would be along the lines of the motion picture developers mentioned above.
I should say that I have not noticed a significant difference in the grain of negatives developed in diluted and un-diluted D-76.
For 35mm work where I want good tone rendition I have lately been using T-Max 100 developed in full strength Ilford Perceptol. Perceptol and Microdol-X appear from their MSDS to be virtually identical. When either is diluted 1:3 the film speed loss is eliminated but the grain becomes about the same as D-76 and one gets moderate acutance effects. At full strength with T-Max the improved smoothness of the tone rendition is quite noticable (at least to me). When my back gets better I will try it on some Rollei negatives to see if the difference is perceptable there.

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

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