The effect of pyro stain on VC paper contrast.

I was taught that a grade 2.5 - 3.0 was "normal contrast" for enlarging due to enlarger flare and when compared to a contact print at a true 2.0. This is why even today I print at about 2.5 - 3.0 for normal enlargements.

PE

Photo Engineer said:

I was taught that a grade 2.5 - 3.0 was "normal contrast" for enlarging due to enlarger flare and when compared to a contact print at a true 2.0. This is why even today I print at about 2.5 - 3.0 for normal enlargements.

PE

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In one of those long threads Steve posted some tone-reproduction cycle curves (source??) and the one using grade 3 paper had the straightest curve.

Well, the curves of VC papers are dependent on the skill of the people making the coating and is always a function of the individual curve for any contrast. This was shown in a paper by Dickerson and Zawadski in Creative Darkroom Techniques nearly 10 years ago.

PE

Ian Grant said:

It might surprise you that by the late 1930's pyro devs, often Pyrocatechin rather than Pyrogallol but still staining developers were being used to give high quality results with 35mm films. The article I'm reading is a sequel to an earlier 1939 article by the same author and he's describing using very dilute Pyrogallol developers with 35mm films

However his approach was not the norm.

Ian

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Maybe I have to say it in a different way: At that time, pyrogallol and particularly catechol was used mainly for large format. I used it for 9x12 cm. Just after WWII, catechol was chosen by amateurs too. This was also caused due to the shortage on chemicals and a catechol developer requires only small amounts of chemicals.
The grain was such that it was not possible to use it for 35 mm. I used developers like D-76 for 35 mm in the 1950's.
In the 1930's we had the economic crisis years. The pyrogallol had to be imported in Germany. But there was no money to import the pyrogallol. That caused a shift to catechol. I have a German paper on the development properties of pyrogallol derivatives. The idea behind it was that these pyrogallol derivatives could be synthesized in Germany. The project was a dead end.

Jed

Maybe Jed, markets varied. Hans Widisch was advocating Pyrocatechin based developers in "Die Neu Foto Schule" in 1938 for 35mm films, and there was commercial use of newer types of dilute Pyro developers in both the UK and US, not dependant on German manufacture.

Many companies including Johnsons were all making and selling Pyro devs for 35mm films before WWII, Johnsons continued with them until pulling out of all chemistry manufacture in the early 1970's. They manufactured raw chemicals as well as compounded developers.

However few were using the early Multigrade papers back in the 1940's

Ian

Ian Grant said:

It might surprise you that by the late 1930's pyro devs, often Pyrocatechin rather than Pyrogallol but still staining developers were being used to give high quality results with 35mm films. The article I'm reading is a sequel to an earlier 1939 article by the same author and he's describing using very dilute Pyrogallol developers with 35mm films

However his approach was not the norm.

Ian

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I am referring to 35 mm photography. In motion picture 35 mm that was different.

I found a catechol formula in a book (1950) and for Tri-X a magnification of 5 was the maximum.It has been used primarily for 120 film.
Pyrogallol, usually had more grain. Amateurs did not use it for developing sheetfilm, because development was done in trays.

Jed

experience

My direct experience is that with a condenser emlarger(tungsten) this is generally true but when I switched to a V54 coldlite I had to bump up my contarst by one filter 3 to 4 etc. Which cut down my range or I had to endure unduly long developement times to try and get the contrast up.

Nicholas Lindan said:

The evidence above is that pyro stain does not correspond to VC filtration. It seems its pass-band is wrong for effecting contrast. It's not the right color.

Pyro stain, it seems, blocks both actinic green and blue - making it ineffective as a contrast filter.

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The so-called evidence above does not show that the stain can affect contrast with VC papers because the tests used to derive the "evidence" were flawed in design.

The flaw is that a uniform stain was applied to the step wedge exposures and that's not the state of the stain in a pyro-developed negative. The stain is not uniform, it varies proportionally to the amount of silver present in the negative.

You also have come to a conclusion that the color of the pyro stain is not the "right color". You can tell this with your eye? What then do you think would be the right color?


To affect the contrast of a VC paper, we need to modify the light so that the ratio of blue light to green light changes from the highlights to the shadows. Your test only looked at the added filtration that would be seen in the highlights, but it doesn't address the amount of filtration that would be present in the shadows. To determine this, I did some tests a few years ago...

Here's the results from one of those tests - I took some negatives that were developed in PMK and Pyrocat and I bleached the silver from the negatives. I then cut some of the wedge steps out of the negatives and put them into a scanning spectrophotometer and measured the absorbance of the stain in the films from these two developers and compared the results. I scanned them from near IR to well into the UV.



See the link below for a bit more info:
http://keyesphoto.com/Resource/TechInfo/Kirk_D_Keyes-PMK_vs_Pyrocat_scan.pdf

Notice that both the PMK and Pyrocat stains have more absorbance in the blue and UV spectrum than they do in the green. (For VC papers, we really only need to look at the blue and green wavelengths.) Additionally, that absorbance increases when the amount of developed silver increases in the processed film. It's this change in absorbance that affects the response of the VC paper to stained negatives - not just some amount of stain that is unvarying in the neg, as your test used.

That's what your tests do not address.

By the way - Negatives from non-staining developers show very little absorbance all the way across the visible wavelengths.

(Also note that the Pyrocat stain has a large increase in the UV as well as less overall absorbance in the visible wavelengths - it's this property that I think prompted Sandy King to persue the use of pyrocatechol (used in Pyrocat) over pyrogallol (used in PMK) as he was interested in it's use as a developer for non-silver printing processes and he wanted a clearer stain for visible light processes.)

Look at the two PMK plots - the dark blue plot is from a highlight area on the negative with the silver removed and the light blue plot from the base+fog of the same film (similar to a very deep shadow area of a neg). At 500nm in the green region, the difference in absorbance between the two plots is only about 0.16 Abs (0.50-0.34=0.16). At 420 nm in the blue region, the difference in absorbance between the two plots is about 0.54 Abs. (0.98-0.44=0.54).

That means the highlights in this film had about 0.38 Abs more in the blue wavelength relative to the green. That is, it had less exposure from blue light. The added blue absorbance is the same as putting in more yellow filtration on your enlarger.

But how much affect does this have in actual printing situations? Since the absorbance curves for neither PMK or Pyrocat are perfectly flat, it's hard to say without more testing. Looking at the amount of blue that is being absorbed relative to the green that is still being transmitted, I guess from this data that it's about a 30 or 40 Y difference in enlarger filtration.

Since the shadow areas of the neg are going to have a little more blue Abs than the base+fog did in my test films, I'd say for practical purposes, it ends up being that the contrast changes about 25Y filtration going from the shadows to the highlights, or maybe 1/2 grade for a neg that is printing with no filtration or with a #2 filter. Of course, this amount of yellow filtration is going to get swamped by a #0 or a #5 filter, and some of it will be lost even with less extreme filtration settings.

So yes, the stain has little effect with a grade #5 filter or a grade #0 filter, but with a neg that prints with a grade #2 or #3 filter, the highlights will be compressed a bit. Think about it this way, it's like adding a bit of yellow filtration only to the highlights, and not much to the shadows - and that will affect the overall contrast of the neg if printed without much other filtration in the pack.

Very good points Kirk, and ones that I missed even after re-evaluating my original answer. I went with the sensitometry and not with the spectral distribution which is important here!

PE

Hi Kirk,

I saw your graph yesterday, I really appreciate the data you presented, it helped put this in perspective for me and I believe you have the tools to carry out a refined follow-up test.

I would say Nicholas' test with a uniform stain is a good scientific test to isolate one variable.

By providing a Zone VIII exposure, he gave a sample near the maximum stain. I know there would be a proportional stain in a step-wedge test or pictorial negative.

I expected a subtle effect, there are many postings that the effect is subtle. Nicholas' test quantifies that effect - it is about 0.4 stops in the highlights - for a Zone VIII exposure and a#5 filter.

I interpret it as follows: If you print a pyro negative that has a Zone VIII exposure using a #5 filter, the yellow pyro stain holding back blue will account for about 0.4 stops less exposure in that Zone than if there was zero effect. If you print the same negative through a #0 filter, there is zero net effect in Zone VIII.

But the negative I would select to print through a #5 filter would not have a Zone VIII exposure, so the hold-back effect I would get is probably 0.3 stop. A third-stop is what I would consider a subtle effect.

In a fine print, a subtle effect can be powerful, so I don't feel this test invalidates anybody's feelings.

It's just too bad the effect occurs mostly where you can't use it, when you need high-contrast filter, you don't have a lot of stain.

The experiment only tests one - and only one - facet of pyro stain: does it alter intrinsic VC paper contrast? No more, no less.

The conventional assumption is that pyro’s highlight effect is due to its ability to modify the ratio of ‘green’ to ‘blue’ (*) light. If this were to be true then the insertion of a highlight-level of stain should alter the contrast of VC paper. The stain should absorb more ‘blue’ than ‘green’ and therefore the paper should show a lower contrast.

But the evidence is that the contrast isn’t changed. Although the stain adds density, it doesn’t alter the ratio of ‘blue’ to green’ to any significant amount.

Pyro stain seems to form simple density.

Negatives developed in staining developers have a different effective HD curve [HD curve as seen by the paper] than negatives developed in other developers. Prints from pyro negatives will look different from negatives developed in other developers. Rodinal negatives look different to Microdol-X negatives and nobody seems to give any particular thought or invest any emotion into to the why of the matter - it just is. Same with pyro - it just is.

As I sell a product to be used with pyro negatives I have some interest in the specific effects of the stain. After all, the product has to work and not just wave its hands. I thought the results of the experiment were interesting so I posted them. Why anyone should give a particular hoot is beyond me.

I've often observed that emotion rushes in to fill the void when hard knowledge is thin on the ground.

As has been said before “I’m tired of all the bickering.”


from http://xkcd.com/386/ [worth a visit]

(*) The terms 'blue' and 'green' are bandied about but until the spectral sensitivity of the 'green' and 'cyan' sensitizers and of the unsensitized 'blue' emulsion are known one may as well call them Thing One, Thing Two and Thing Three. The experiment makes no dependence on the color of the stain - it could be anything, it doesn't matter - the question is "Does it affect intrinsic contrast?" The answer is "No."

Correspondence closed

Kirk;

I cannot get to your web site, and the absence of the spec curves removes a powerful visual statement to your post IMHO.

After looking at your curves and those Nicholas posted, there is a chance that the "real" curve for a true pyro negative would be the sum of the two curves posted by Nicholas, ie, a lowering of contrast with the stain. At least this is one possible prediction by observation of your curves and his curves. The only way to prove it one way or another is to do it.

PE

Your test only looked at the added filtration that would be seen in the highlights, but it doesn't address the amount of filtration that would be present in the shadows

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If one has a paper that prints as a "2" with no filtration, and the pyro stain in the OP is similar to "2" filtration, then the amount of pyro stain in the highlights or shadow does not affect the contrast.

But it apparently can. This is because the stain itself varies from low to high densities. It is like having a variable density #2 filter for your VC paper or better still like split grade printing.

PE

Photo Engineer said:

This is because the stain itself varies from low to high densities.

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Of course it does. The stain is [mostly] proportional to silver. Or are you saying something different?

I am saying:

1. The stain as a constant filter does not change contrast. You have shown that in the OP.

2. The stain varies with each step and has density in the region of the spectrum that papers are sensitive to, especially MG papers.

So... Given that, what might happen is this....

Since the filter does not change contrast, but does vary in density with each step, it offers the possibility of a variable density filter from toe to shoulder. If it acts that way both you and Kirk are correct but what you see is the DIFFERENCE between the two curves you posted (I think I said sum in an earlier post). This is due to the fact that at Dmin there is no filter and at Dmax there is maximum filter and so the final curve is the line drawn between the two curves you show.

Visually, one might then suspect that the filter caused this due to its very nature, but this is probably not the case as you have shown. Rather it is due just to having an extra density filter present (much of which is in the UV region).

The experiments would have to be done to show the validity of what I say, but I am basically splitting the difference between what you and Kirk are showing.

PE

Nicholas Lindan said:

Of course it does. The stain is [mostly] proportional to silver. Or are you saying something different?

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It does

Didn't someone one say that in Post #15 of this thread ?

"So thinking laterally assuming max stain is equivalent to Gd 2 in the highlights then that drops proportionally to the shadows where there's no stain."


Kirk's data backs up the various article showing a clear difference in behaviour with different wave lengths of light.

What I can't understand is why people bicker & dispute the facts shown clearly with tests & measurements that are repeatable.

Anyone who uses staining developers seriously knows how they print, but there is a huge issue of variability between how films stain, effects of different developers on different films, and we should add differences between developers & variable contrast/MG papers as that's what we are looking at in this thread.

Ian

Photo Engineer said:

offers the possibility of a variable density filter from toe to shoulder.

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That's exactly what it does. I didn't know there was ever any debate on the issue.

Nicholas Lindan said:

That's exactly what it does. I didn't know there was ever any debate on the issue.

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There wasn't because no-one thought of it like this or rather didn't write it that way

Ian

For me, this everything looks extremely simple .

1) Everyone knows that (the total density of) stain is proportional to silver density, no need to prove.

2) Everything that counts is whether the blue-to-green ratio (can be called "color") is same at lower and higher stain densities, or does it change.

And, Kirk has shown undoubtedly that it changes, and has definite numbers how much it changes -- after we define "blue" and "green".

So, what still lacks, is:
what are the exact spectral sensitivities of typical VC papers? This information is needed so we can define "blue" and "green" from the viewpoint of the paper, and to exactly define how much the blue-to-green ratio changes based on Kirk's graph.

After you have that, you have the answer. Then you can go on debating and pickering about how significant this effect is, and whether it can be seen or not. Don't forget that some people claim they can see it, and some claim they cannot see it... It will be a hard battle.

Good luck for everyone .

Nicholas Lindan said:

That's exactly what it does. I didn't know there was ever any debate on the issue.

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Kirk raised the issue in his post, as did several others which prompted me to clarify the information already presented. I had no problems after my unfortunate misread of the OP. Your curves were perfectly clear.

PE

hrst said:

... So, what still lacks, is:
what are the exact spectral sensitivities of typical VC papers? This information is needed so we can define "blue" and "green" from the viewpoint of the paper, and to exactly define how much the blue-to-green ratio changes based on Kirk's graph.

After you have that, you have the answer. ...

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Don't we also need the spectral power distribution of the light source? What about the UV filtering of the lens? It doesn't help if VC paper is sensitive to UV if the light/lens system does not produce any of it or doesn't allow any of it to get to the paper.

RalphLambrecht said:

Don't we also need the spectral power distribution of the light source? What about the UV filtering of the lens? It doesn't help if VC paper is sensitive to UV if the light/lens system does not produce any of it or doesn't allow any of it to get to the paper.

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IMO, you are making it more complicated than it is!

I can't see how the spectral power distribution of light source would change how the stain works, of course given that the spectral distribution is usable for multigrade printing to begin with, and given that we are not very close to extreme grades.

So, let's take any light source that is capable of producing different contrast grades. To do this, it needs to emit both blue and green in practical amounts. The spectrum shape is quite irrelevant, only thing that matters is that the bands absorbed by the silver halide or sensitizing dye exist.

VC contrast filter just removes these bands in different proportions depending on filter grade. If the light source changes, we may need to change the contrast filter to compensate, but after that, we are again back to the same blue-green ratio determining the contrast.

UV indeed is problematic, and important as Kirk's data shows! The blue-green ratio difference comes bigger the more towards UV we define our "blue". The differences in UV filtering in different systems may be one of the reasons why some people find the effect of stain and others do not. It is at least sure that multigrade filters have to filter out UV somewhat to work well. So, leaving the filter out might change something. And some machines may have additional UV filters. Even the light bulb's front glass might have such a filter.

Here is a sensitivity test of Ilford MGIV (a wedge spectrogram in technical terms).

There is a lot of UV, I assure you, but I cannot capture that with my equipment.

Most enlargers have UV absorbers and heat absorbers to prevent problems, but who knows. I do know that there is a lot of UV absorption in Pyro negatives.

PE

hrst said:

IMO, you are making it more complicated than it is! ...

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There is a thin line on APUG between being blamed to over-simplify and to over-complicate. Let's see:

hrst said:

... The differences in UV filtering in different systems may be one of the reasons why some people find the effect of stain and others do not. It is at least sure that multigrade filters have to filter out UV somewhat to work well. So, leaving the filter out might change something. ...

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That's what I was getting at.