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Re: Pyro Developers Question.From: dickburk@ix.netcom.com (Richard Knoppow) "Darkroom User" <Darkroom.User.69f9028@photobanter.com> wrote in message news:Darkroom.User.69f9028@photobanter.com...
Boy, have you opened a can of worms here:-) Pyro was the first organic developer discovered and applied c.1860. Previous developers were inorganic and nowhere near as efficient. Pyro remained a favorite for the next fifty years but was eventually supplanted by developers employing a combination of Metol (AKA Kodak Elon and a bunch of other names) and hydroquinone. These two in combination can make a very wide varity of developers. Pyro, in the right sort of formula produces a stain image along with the silver one. The stain image is usually a yellow or greenish brown. It increases the effective printing density when the printing material is sensitive only to blue light. Pyro became popular when it was discovered that the stain image would act as a contrast mask when films were printed on variable contrast paper, tending to lower the contrast of the highlights. This was considered desirable because some modern fils, tabular grain ones like Kodak T-max for instance, can produce extremely high maximum densities. Because the traditional Pyro developers tended to be somewhat grainy some more modern ones were devised. PMK in particular has become popular. However there may be problems with it, for one thing the books on photographic chemistry warn that borax is not compatible with Pyro and should not be used in Pyro developers. PMK uses "Kodalk", Kodak's trade name for sodium tetraborate, a borax compound. I've seen several explanations of why this is OK in this particular formula. Traditional Pyro developers are mixed from two or three stock solutions. This is because the most Pyro developers are vulnerable to oxidation from the air and are not long lived when mixed. When Pyro was the principle developing agent a great deal of work was put into devising _non-staining_ formulas. This is because the effect of the stain on printing density is not easily predictable and it was found in motion picture practice that obtaining consistent results was difficult. When D-76 was introduced in 1926 it very rapidly displaced all other developers for motion picture negative processing. This was partly because it produced fine grain negatives but also because it was more consistent and controlable than previously used developers. Pyro has a couple of advantages especially for tray use: while it is itself rapidly oxidized it does not produce aerial fog, secondly, its a fairly good desensitizer so is advantageous when developing by inspection. The short life was addressed in some two part forumulas which included Metol. In these developers the Metol is present mainly to preserve the Pyro although it also functions as a developing agent. Kodak D-7 is an example. The three part developer, often called ABC developer, evolved over the years to the point where the published formulas were all the same. Kodak D-1 is a classical ABC developer. These are still quite satisfactory but are probably a bit grainy for 35mm film. Some early formulas used acetone as an intermediate for generating carbonate (actually hydroxide) in solution. Because the acetone is volitile these developers tend to be inconsistent and are the main reason that Pyro got the reputation for being inconsistent. The later formulas using sodium carbonate are much more satisfactory but one still has the problem of determining actual printing density and contrast due to the stain image. BTW, the stain is composed of a humic acid pigment, not a dye, and is probably more permanent than the silver image. Pyro will also work as a warm tone print developer but the Coloring Pictures">color may not always be a desirable one. I collected a bunch of Pyro formulas which someone kindly posted to their web site. It appears as a PDF at: <> There are some good articles on Pyro developers on the web: A Google search for Pyro Film Developers will find lots more. -- -- Richard Knoppow Los Angeles, CA, USA dickburk@ix.netcom.com
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