I don't understand about Pyro

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According to Gordon Hutchings' book, Pyro (PMK) stains most heavily in areas where there has been maximum reduction of Silver Halide. At the same time it is said to prevent blocking up of highlights in the print. Since highlights are blocked up because there is already too much negative density, I don't understand why adding Pyro stain doesn't make it even worse instead of better.

-- Bill Mitchell (bmitch@home.com), January 13, 2001


For the same (effective) CI the silver density is about 2/3 that of a non-pyro neg developed to the same CI; the remaining 1/3 density is stain. Or iow, as far as light transmission's concerned the density is the same.

Or to say it differently, it's as if you developed the film less and then added a proportional stain, giving the same overall density.

I think the term "block" is misused; traditionally it means that additional exposure doesn't result in increased density, or the curve slope is flat, no contrast. I believe what Hutchings is referring to is negs that simply have a far greater density range than can be printed.

When printed on VC paper, the color of the stain acts as a lower-contrast filter proportionally to density, so that the higher the density the lower the printing contrast; this dramatically compresses the lighter tones.

The same degree of compression of the high end can be obtained with extremely-compensating development.

Note that reducing contrast, whether via stain and VC paper or compensating development, on a practical level reduces the slope of the curve and at some point _will_ block, or there won't be enough contrast to make a printable detail.

To me, this usally makes prints that have light tones that look like flat grey muck and imho is only useful when there's an extreme brightness range in the light tones in the scene.

-- John Hicks (jbh@magicnet.net), January 13, 2001.

Thanks, John. Does this mean that so-called blocked up highlights can only be "tamed" by printing on VC paper, or is there some sort of compensating effect of Pyro development, in addition to the stain?

-- Bill Mitchell (bmitch@home.com), January 13, 2001.

> Does this mean that so-called blocked up highlights can only be "tamed" by printing on VC paper, or is there some sort of compensating effect of Pyro development, in addition to the stain?

The stain causes the compensating effect on VC paper.

When a pyro neg is printed on graded paper or used for alternate printing methods (platinum etc) the stain is simply printing density. This can be of great benefit for alt methods because sometimes the film's silver image simply can't be developed to such a high contrast and D-Max, the grain would be huge or the curve shape would be weird.

When a pyro neg is printed on VC paper the greenish-yellow stain acts as a proportional low-contrast filter which gives the compensating effect.

Pyro doesn't provide compensating development by itself.

A couple of other things...

There are several pyro formulas that are non-staining; you could even make PMK non-staining by using acid stop, acid fix and not giving the alkaline rinse (used developer or Kodalk).

Barry Thornton's DiXactol is also a staining developer, but since the stain is brownish it doesn't give the highlight compression when negs are printed on VC paper.

Pyro negs aren't exactly fine-grained and sharp; it's somewhat more like chunky grain and mediocre acutance, but of course the larger the format the less concern there is over those characteristics. It might be horrible in 35mm and fine in 8x10.

-- John Hicks (jbh@magicnet.net), January 13, 2001.

I agree with John Hicks that Pyro (I use PMK) negatives look best when you are photographing a brightly lit scene with a long scale of brigtness. In more evenly lit scenes the variable contrast effects of the stain require printing on higher contrast paper.

For those (flat lit) scenes I prefer the results I get with D76, 'though generally I'm not organized enough to switch back and forth from D76 to PMK.

-- Don Karon (kc6d@arrl.net), January 14, 2001.


You should take a look at Carl Weese's article on Pyro in PhotoTechniques printed last summer. He explains the relationship between the type of process being used and the light wavelength required to print it. I'm afraid that I don't have the information in front of me to give a better answer. I belive Hutchings says somewhere in his book that Pyro stain replaces the silver which is why it doesn't become too dense to print under an enlarger light source. The stain, however, is more absorptive of UV rays required for alternative processes, resulting in greater density.

-- Kevin Kemner (kkemner@tateandsnyder.com), January 15, 2001.

Maybe this article?

http://www.phototechniques.com/previous-articles/nov99-weese/nov99- weese.htm

-- Mani Sitaraman (bindumani@pacific.net.sg), January 22, 2001.

Bill alerted me that the link above does not work.

Try going here

i.e. to

http://www.phototechniques.com/previous-articles/sample_article.htm and then scrolling down, and clicking on the link (in the long vertical box on the right) for Carl Weese's article on Pyro Development for dual use negatives.

-- Mani Sitaraman (bindumani@pacific.net.sg), January 25, 2001.

One more time...


-- Mani Sitaraman (bindumani@pacific.net.sg), January 25, 2001.

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