Selenium-why different tones w/ different papers?

[austin granger]

Hey all. I've been experimenting with how different papers tone in selenium. Can someone (and I know someone can) tell me just why it is that different papers respond so differently when toned in selenium. That is, with all other things being equal (same developer, same time in developer, same fixer, same selenium dilution, same time in selenium, etc) one still gets an incredible variety of hues, dependent on the paper type. Technically, what is going on here? Just curious...

I guess a related question could be; what causes the color in a black and white print?

Oh, and if anyone is searching for a specific tone for their b/w fiber prints, I might be able to help you. I've got everything from a cool Ansel eggplant to a subtle Weston brown to a rather ridiculous red...

[paulr]

Well, all else is equal, but the variable that you're changing--the paper--is a huge one.

I doubt there's ever been thorough research on the chemistry of toning. One factor that makes a huge difference in the color of a print (toned and untoned) and also in the image's reactivity with all kinds of chemicals, is the grain size of the silver in the emulsion. I'm specifically not talking about visible image grain, but rather the microscopic grain of the paper emulsion itself. A long, long time ago, when things were simpler, paper emulsions could be classified as silver chloride (very slow, very fine-grained), silver bromide (fast, large-grained), or some mixture of the two (chloro-bromide or bromo-chloride, depending on the ratio of silver halides).

The finer the grain, the warmer the image tone, and the more reactive to most toners (also, very likely, the more reactive with contaminants).

Where the subtle color shifts come from--the different shades of green, the warm or cool shades of brown--I don't have a good explanation for. In fact I've never seen one.

[Cesar Barreto]

Yes, papers are quite different indeed and multi-contrast emulsions show many subtleties related to development, processes, dilutions and so on.
Tim Rudman made a nice job covering almost all steps on toning on his book "The Photographer's Toning Book - The definitive guide", by Amphoto Books. Although some can argue about the "difinitive" statement, it's quite complete and updated, so it's unquestionably a must on bibliography.

[Merg Ross]

Austin, regarding all things being equal, developer temperature and oxidation are important factors when considering image color. Also, I believe you will find that faster paper emulsions will produce colder tones; for example, the difference between Ilford Multigrade IV and the slower Ilford Warmtone.

[Ralph Barker]

Although you've kept other elements consistent, Austin, don't forget that different developers can also result in different post-selenium colors with the same paper. For example, my understanding is that selenium toning Ilford FB Warmtone developed in Zonal Pro Warmtone Developer you will get a warm brown tone instead of the usual eggplant color.

[Struan Gray]

Despite over a century of empirical evidence, and plenty of reliable-ish recipies for particular effects, predicting the colour of small grains of silver or silver-selenide is still a hard-to-impossible problem in Solid State Physics (my own field). Only in the last ten years or so have microscopes become powerful enough to say what the actual structure of such grains actually is, and the theoretical calculation of their optical properties is still rather hit or miss.

Metals like gold and copper, and the grains in warm/cold tone emulsions are coloured because of a collective excitation of the electrons in the material. This is unlike the colours of insulators like, say, natural sapphire, which is caused by excitation of single electrons on their own and is much easier to calculate. That said, the colour of a piece of copper you can hold in your hand can be accurately predicted because the excitations are in the bulk where the crystal symmetry dramatically simplifies the equations you need to solve. A microscopic ('nanoscale' is the current buzzword) crystal like a film or paper grain doesn't give you that luxury. Surface effects on the outside of the grains become highly important (the atoms move about, and the electron energies are different); the immediate environment - gelatin in photography - has an influence, and the presence or absence of other similar grains nearby also contributes. Worst of all, you have to consider the electromagnetic field of the light and the behaviour of the electrons as a single entitiy - you cannot just solve them seperately. The lack of symmetry, the need to consider all the particles at once, and the coupling of light and matter makes the problem hard, even for boffins.

The good news is that all sorts of fascinating new science is lurking in the midst of that complexity. The research I know about is aimed at applications like flat panel displays, solar cells and electrooptic devices rather than photography, but the information carries across and I know for a fact that the emulsion scientists are keeping their ears to the ground. It seems a bit ironic that we shall probably only fully understand how photographic emulsions work when they have become redundant.

[Struan Gray]

I should have also said that the reason you get such a range of colours is that toning changes the grain size, the grain shape and the grain material, all of which can affect the colour you see, and in different ways. When toning, silver is converted to silver selenide, with the smallest grains converted first and the larger ones converting more slowly, so the toning spreads from the fine-grained highlights to the coarse-grained shadows as you prolong the bath, but each part of the tonal range can have a different colour because the original grains were different, and because the toned grains are different again.

[Gem Singer]

Hi Austin,

Regarding your question "what causes the color in in a black and white print?" Aside from the amount of silver chloride, silver bromide, or silver iodide in the emulsion (each giving a slightly different tone to the final print). You also need to consider the color of the paper base on which that emulsion is coated.

For example: the emulsion of Ilford MG IV fiber base paper contains an increased amount of silver bromide, and it is coated on a neutral white paper base that has been treated with fillers and optical brighteners. For the most part, it does not change color in Kodak Rapid Selenium Toner. However, toning in KRST does produce an increase in the D-Max, resulting in deeper black and a cold toned look to the print.

On the other hand, the emulsion of Ilford Multigrade Warmtone FB paper contains an increased amount of silver chloride, and it is is coated on a buff (cream) colored paper stock. In other words, it contains a warmer toned emulsion that is coated on a warmer toned paper base. It tones very well in KRST, resulting in a warmer looking print.

[paulr]

It seems unlikely that with any emulsion devised in the last 30 years or so, that old categories of chloride, bromide, and iodide still mean much. Modern emulsions are more complex than that--at least according to an Agfa technician I talked to in the late '80s.

Besides, in the cases of all these emulsions, the final image is just silver. Noting that one halide or another gives warmer results tells us nothing about why, or what's actually going on.

On another note, one thing that I discovered is that the degree of development (a factor of development time and temperature with any given paper/developer combination) radically influenced the way the paper toned. Even if I couldn't see much effect from the change of development before toning, the final color (after selenium, or particularly after nelson gold toner) would vary a lot. I had a hard time controlling color before I figured this out.

[Gem Singer]

PaulR,

Perhaps that's the reason why Ilford (and others) recommend developing their papers to completion. For Ilford Multigrade Warmtone FB paper, which I have been using ever since it was introduced a few years ago, 3-5 minutes does not an seem to be an extremely long developing time. I usually add some benzotriazole restrainer solution to my PQ type developer. As a result, the development times are prolonged to begin with.

However, any variation of the tone that I've observed seems to be a function of the time , temperature, and dilution of the KRST toning solution, in my experience with that particular paper and toner. I'm sure that the final tone from KRST would also vary with the type of paper used and whether, or not, it was developed to completion.

As a final note, I usually wash and dry my prints before toning. Re-wetting, toning, and a final wash (with a wash aid) are then done at a later time.