The effect of pyro stain on VC paper contrast.

Photo Engineer said:

Well, we do not know the form of the silver that is created by the staining developer, do we? Silver itself has color! It can be warm or cold toned. We cannot see it through the "stain". That further complicates the test.

PE

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This has been questioned before. The brown ' proportional stain ' of a catechol developer is often not thought to be stain but the color of the silver.

Jed

Jed Freudenthal said:

This has been questioned before. The brown ' proportional stain ' of a catechol developer is often not thought to be stain but the color of the silver.

Jed

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Well, look back at the spectral scans I posted earlier and you can see that the stain color is not all from silver and it certainly largely from the stain.

I have scans of non-stained film and it varies little until you get into the UV and then the gelatin itself starts to absorb strongly.

Jed Freudenthal said:

The brown ' proportional stain ' of a catechol developer is often not thought to be stain but the color of the silver.

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I don't think so, because complete bleaching of a negative developed in Pyrocat-HD leaves a nice brown (though of course milky, unless fixed) image behind. I've tried it myself. The stain is definitely brown.

There have been suggestions here that the ratio of 'blue' to 'green' changes with negative density. A bleached, stain revealing, negative shows a uniform color:



The color change for a 1/2 grade change in contrast is shown by the surrounding Kodak VC filters.

A contrast altering level of color change isn't evident in the pyro negative.

Someone posted spectrophotometer plots that purported to show color change. Unfortunately, without a plot of the B+F absorbance the plots can't be properly interpreted.

I'm not shying away from spectrophotometers - I design them for a living. A large part of my engineering practice is developing instrumentation for clinical chemistry - there is a good chance your blood has flowed through one of my designs. I have designed spectrophotometers that can measure to 0.000003 OD in a sample spinning past on a centrifuge rotor - the duration of the flash that illuminated the sample was 1 microsecond. So I do know how to measure absorbance. The effects here, however, are gross - they are discernible to the eye without any instrumentation; experiments anyone can make.

The question isn't one concerning spectral plots but finding if the stain does or does not act as a VC filter. Experiments with MG paper indicate it doesn't.

Nicholas

This is pretty convincing evidence. Thanks for sharing these results.

Nicholas Lindan said:

The question isn't one concerning spectral plots but finding if the stain does or does not act as a VC filter. Experiments with MG paper indicate it doesn't.

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Thank you,

Kirk Keyes said:

Well, look back at the spectral scans I posted earlier and you can see that the stain color is not all from silver and it certainly largely from the stain.

I have scans of non-stained film and it varies little until you get into the UV and then the gelatin itself starts to absorb strongly.

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You made spectral scans with pyrocat as developer. In pyrocat there are more developing agents. The l structure of a pyrocat silvercrystal is different from that of a catechol developer like the Windisch developer, where catechol is the only developing agent. The optical properties of the silver crystals are different. It is like with the warm color of chlorobromide papers and the cool color of bromide papers.

Jed

Jed Freudenthal said:

You made spectral scans with pyrocat as developer. In pyrocat there are more developing agents. The l structure of a pyrocat silvercrystal is different from that of a catechol developer like the Windisch developer, where catechol is the only developing agent. The optical properties of the silver crystals are different. It is like with the warm color of chlorobromide papers and the cool color of bromide papers.

Jed

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You may be right that there is a difference in silver structure between Pyrocat-H and Windisch. I can't say, as I've never used Windisch.

However, people need to keep in mind that "Catechol" is a name for 1,2-dihydroxybenzene, which is the internationally accepted name for this compound.

So names that are synomyms for 1,2-dihydroxybenzene are:

1,2-benzenediol
catechol
pyrocatechin
pyrocatechol
and probably a few others...

Pyrocat-HD uses pyrocatechin (from the formulation here: http://unblinkingeye.com/Articles/PCat/PCat2/pcat2.html ) and phenidone.

I don't have any info on how the phenidone affects the color of the tanning stain.
pyrocatechol

Nicholas Lindan said:

Someone posted spectrophotometer plots that purported to show color change. Unfortunately, without a plot of the B+F absorbance the plots can't be properly interpreted.

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Someone... That was me.

Please review the plots I posted - It clearly states that for each film/developer shown, there is a spectral scan from one of the densest steps from the step wedge contact (labelled as "Step 1 Bleached" for the TXT320 in PMK and "Step 2 Bleached" for the FP4+ in Pyrocat) as well as a corresponding spectral scan from the B+F of each test film.

I'm sorry if that was not plainly labelled enough for you. If you need to, please click on the graph so it displays larger so you can read the labels.

(Please note that I redid the colors of the lines so that the densest step scan for each film/developer combo is a solid line and the corresponding B+F scan for each combo is a dashed line. I left the original graph online so you can verify all that changed was the color of the lines and the line style.)

Here it is again four your review:

Nicholas Lindan said:

There have been suggestions here that the ratio of 'blue' to 'green' changes with negative density. A bleached, stain revealing, negative shows a uniform color:

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Nicholas Lindan said:

I'm not shying away from spectrophotometers - I design them for a living. A large part of my engineering practice is developing instrumentation for clinical chemistry - there is a good chance your blood has flowed through one of my designs. I have designed spectrophotometers that can measure to 0.000003 OD in a sample spinning past on a centrifuge rotor - the duration of the flash that illuminated the sample was 1 microsecond. So I do know how to measure absorbance.

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Perhaps you could use just a regular, old photographic quality color densitometer and read the steps of your bleached step wedge. (And hopefully you have a duplicate that was not bleached so you can compare that for use as well.)

My color densitometer shows that both films that I scanned had a large difference in absorbance between the blue and green channels of the stained film. Can you check you film and see if you get a similar difference?

I suspect that you'll find a big difference in densities.

Kirk Keyes said:

You may be right that there is a difference in silver structure between Pyrocat-H and Windisch. I can't say, as I've never used Windisch.

Pyrocat-HD uses pyrocatechin (from the formulation here: http://unblinkingeye.com/Articles/PCat/PCat2/pcat2.html ) and phenidone.

I don't have any info on how the phenidone affects the color of the tanning stain.
pyrocatechol

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The information that in a pure catechol developer, the color is the result of an optical effect came from a German paper, published long ago. It will take some time to retrieve that paper. What I recall is that the size of the grain ( or crystal, filament) is responsible.

Anyway, I am using pure catechol developers, and the pH is certainly different from a developer like pyrocat. In the buildup of the grain, the pH plays a role. The structure of a pure catechol grain will be different from that of a pyrocat grain. And as a result the optical effects.

When I use the pure catechol developer with different films ( different primary halide crystals), I notice different colors. In Fortepan 200 their is a clear light brown color, with FP4+ you will noting no visible color change. That doesnot mean there is no color change. On a VC paper you will observe the differences. That makes VC paper valuable, but difficult to understand.

Jed

Jed Freudenthal said:

The information that in a pure catechol developer, the color is the result of an optical effect came from a German paper, published long ago. It will take some time to retrieve that paper. What I recall is that the size of the grain ( or crystal, filament) is responsible.

Jed

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It's true that the choice of developer and time/dilution effects the size of the grain and so the colour of a silver based image but this is really only applicable to warm tone papers and chloro-bromide / bromo-chloride emulsions.

One additional problem when comparing staining developers to non-staining is there's slight staining with many developers containing Hydroquinone.

Ian

Ian Grant said:

It's true that the choice of developer and time/dilution effects the size of the grain and so the colour of a silver based image but this is really only applicable to warm tone papers and chloro-bromide / bromo-chloride emulsions.

Ian

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This is also applicable to film emulsions. A review paper on the subject is written by T.H. James, The mechanism of development, published in The Theory of the photographic process, 4 th edition. In particular the subject on filament formation (p.390 ff) deals with this subject.

And, one can hardly imagine that the grain structure is not affected by the development conditions. The ionic silvertransport during the crystal buildup is controlled by all these parameters.

Jed

Jed;

It is correct that film "color" varies as a function of developer and density and the reference you state is just one of many pieces of data on this subject that has been published. It should be more widely known, but sadly it is not.

PE

While I know that grain can had different colors associated with the size and shape of the developed silver, it needs to be visible with transmitted light to affect VC papers. The tanning stain in developers like PMK, Pyrocat, or WD2D is definitely transparent and can have more effect than simple neutral density.

Here's the densitometer readings of one of the sheets of film in the spectral scans I posted above. It's for the sheet of TXT320 I developed in PMK 1:2:100. I exposed the sheet under my Saunders 4500 enlarger with a 80A filter over the enlarger lens to convert the color temp of the enlarger light from about 3000K to about 5500K.

I used a Stouffer 21 step 4x5 transmission tablet. Step 2 of my tablet has a density of 0.19 density, and I used a dense part of the middle of the tablet for the B+F exposure. To ensure that I was truely getting no light through the tablet in that region, I placed a strip of silver mylar tape.

Density readings were made with a Noritsu DM-201 color densitometer using Status M filtration and calibrated with a Stouffer transmission calibration film. My understanding is that Status M filters have peak transmission at about 450, 545 and 640 nm for Blue, Green, and Red respectively. The responses are fairly narrow, roughly on the order of 40 nm spectral width. The Noritsu appears to measure the visible somewhere between green and red - I have no info on that.

The sheet I used for the spectral scans had the following Visible (V), Blue (B), Green (G), and Red (R) density readings -

Before bleaching this sheet, it had the following readings -

Unbleached TXT320 4x5 - Step 2 area:
V: 1.62
B: 2.33
G: 1.67
R: 1.52

Unbleached TXT320 4x5 - B+F:
V: 0.10
B: 0.18
G: 0.11
R: 0.08

After Bleaching this sheet, it had the following readings -

Bleached TXT320 4x5 - Step 2 area:
V: 0.13
B: 0.61
G: 0.15
R: 0.07

Bleached TXT320 4x5 - B+F:
V: 0.07
B: 0.13
G: 0.06
R: 0.05

As you can see, there was very little change in the B+F density readings of this film from before bleaching to after bleaching. On average, the bleached film is only 0.04 density readings lower for all channels of the densitometer.

It's been stated in this thread that the color of the stain does not change with stain density. I believe that the data I've presented shows that the "color" does change - actually, it's the saturation of the color that changes.

PMK stain in my experience has a yellowish tint to it. It's not a very strong yellow, but as the stain increases in density, so does the blue absorbance of the stain and hence the amount of yellow increases.

You can see that in the densitometer reading I presented above, as well in the spectral scans I presented. In the spectral scans, the amount of blue absorbance increases faster than the green absorbance. The red absorbance is affected very little by the stain.

For this reason, I figure that the readings made with the red channel with the densitometer are probably very close to representing the actual density that is present from the developed silver in the film alone. If you compare the readings with a non-staining developer, the density on the film can change very little regardless of which channel is used to make the reading. Here's some measurements of an unbleached sheet of TXT320 4x5 that was developed in XTOL 1:1 at the similar density as the sheet above had for visible reading -

V: 1.67
B: 1.72
G: 1.67
R:1.65

As you can see, the XTOL does not cause a large difference in color density readings.

VC papers will be affected by changes in the relative amounts of yellow and magenta filtration that is used on the exposing light source - If you've used a dichroic enlarging head to print VC papers you will agree that small amounts of filtration have have an effect on the contrast of the print. I often use adjustments of 10 or even 5 points of filtration when setting the filter pack for a print.

I think we can all agree that if there is an equal amount of blue and green absorbance in the pyro stain there will be no effect on the VC paper - the paper will see those equal amounts of density as being simple neutral density.

The densitometer readings of the unbleached film on the Step 2 exposure area shows an excess of 0.66 density from the blue and the green channels (2.33B - 1.67G = 0.66B excess). That's quite a large amount of yellow filtration that is being added to the film from the stain. After bleaching, that same film showed 0.46 more blue absorbance than green (0.61B - 0.15G = 0.44B excess ). Even after bleaching, there is a large excess of yellow filtration (or blue absorbance if you like) left in the film.

When I calibrated my Saunders 4500 dichroic enlarging head against my Ilford Multigrade printing filters, this much yellow filtration was equal to about a Grade #1.5 filter. It's a significant change from printing with no added filtration.

And to show that the filtration changes from the shadows in the film to the highlights, looking at the B+F of that sheet, it had a difference between blue to green of 0.07 more blue for the unbleached film (0.18B -0.11G = 0.07B excess), and after bleaching it was still 0.07 more blue (0.13B - 0.06G = 0.07B excess).

So you can see from these measurements, there is yellow filtration being added to the highlight areas of the developed film from the pyro stain that is not present in the B+F or shadow areas. It's this increase in the saturation of the stain that has an effect on VC papers.

Page 6 of this pdf from Kodak has a nice graph of the Status M densitometry filter absorbances if anyone is interested:
http://motion.kodak.com/motion/uploadedFiles/printing_density_1007.pdf

Good article Kirk. Tom is a neighbor of mine and we used to share an office. We also used to car pool to work. I'll have to ask him about this work sometime. I didn't know what he was up to these days.