Kodak z131 (Flexicolor): Why is pre-soak not recommended?

Hi all,

 

Tonight, I plan on processing with Kodak C-41 chemistry for the first time. I noted that the Kodak z131 manual does not recommend a pre-soak stage for rotary tank processing. While I am using a Paterson tank, I feel their recommendation may still hold. As far as I know, the pre-soak stage is just bring the temperature of the tank and film up to 38C/100F. Here's their recommendation:

 

Do not immerse the film in a warm water pre-soak. Warm-up step is done by warming the outside of the tube with hot air or in a tempered water bath.

 

Some part of the emulsion runs off after the pre-soak. (I think the water is usually a blue-ish color.) On one hand, maybe those chemicals are really inteded to be their during development. On the other hand, seems like it might be good to keep those 'blue chemicals" out of the developer working solution. But, no science to back any of that.

 

Anyone have a more scientific answer?

 

Thanks!

I can say things, but they'll be hypothetical. I have substantial experience with C-41, but it's primarily in high-volume replenished systems; never with a prewash. So I can't say for certain what would be the effect of a prewash.

 

Now, dry film has a certain thickness of the emulsion. When it gets wet, it swells (some people compare it to a very thin sponge). Sure, it's on a microscopic level, but development also works on such a level. In normal C-41 processing the developer enters a dry film emulsion, and everything is fine-tuned to work from that starting point. The film swells as the developer diffuses into it, and the developing agent becomes locally (on a microscopic level) exhausted and byproducts are released. And things diffuse in and out of the emulsion. Anyway, the net result is, ideally, a well-controlled process with "good" result.

 

If you were to precede this process with a presoak, the emulsion will be already swollen with water. The developer will have to diffuse through a greater distance, and diffuse into water. So the chemicals concentrations within the emulsion will also be different, at least initially. If I had to guess as to the actual results, I'd say that the bottom dye layer would be most affected, at least for the first half--minute or so, until the water is mostly counteracted.

 

I have no idea how significant this would be, but I suspect that most people would not see a difference. Especially since almost everyone works from scanned film nowadays, and ... well, high-quality color is a rarity in my view. Now, if you do multiple rolls from a batch of developer, the prewash from each roll is gonna dilute the developer more and more, so...?

 

If there was a well-controlled high-quality lab doing optical prints of, say a studio portrait, I'd bet that they would see a difference, likely a color cross in the skin tones. And the more diluted the worse it would get. But a seriously high-quality lab isn't gonna be using prewash.

 

You might wonder why Kodak didn't initially design around a prewash. Well, these processes were designed for lab use, where a stable, high quality, and economical product has always been important. And replenished systems fit the bill. The main thing a prewash would do is to dilute the developer, requiring more replenisher. So the operating cost would go up, and it would produce a higher effluent load. So it's just an overall bad idea in the pro world. Now, if you have a system where you can't get a quick, clean immersion into the developer, then a prewash might be beneficial. But I tend to see it more as a bandaid being put on a bigger problem. Anyway, just my two bits.

Anyone have a more scientific answer?

I read a patent some years ago for a substance called 'mercapto-tetrazole' or something similar. In brief, the patent described the action of the chemical as being a selective restrainer; holding back development of the top layer(s) of a 3 layer colour film. Such that the development was evened-out across the depth of the emulsion.

 

I'm guessing, that if such a restrainer was incorporated in the film, then a pre-bath might wash it out or upset its action in some other way.

 

Plus the C-41 developer timing is quite brief, and the dilution and delay caused by a pre-bath might well cause under-development.

 

Whatever. I've always followed the maker's instructions closely when processing C-41 in a Jobo rotary machine, with good results. So no need to mess with a procedure that obviously works.

Some part of the emulsion runs off after the pre-soak....

With B&W film, especially T-Max, that's the anti-halation dye. The same dye isn't used in colour film.

 

My experience with processing large format sheet film in a rotary tank is that, with B&W, a pre-bath is beneficial in preventing foaming and filling marks. However, the same doesn't seem to apply with 35mm and rollfilm. Nor with the C-41 process.

Edited July 3, 2020 by rodeo_joe|1

Modern color films are multi-coated –overcoat—UV filter coat—fast yellow—slow yellow—interlayer-fast magenta—slow magenta—interlayer-mid magenta—slow magenta—interlayer—fast cyan—mid cyan—fast cyan (again)—annihilation—subbing—base. Additionally, preservatives to prevent organic growth, hardeners to reduce gelatin swelling, rate of infusion controllers, sequestering agents to control reactions from stray metal ions, acids and bases to adjust pH, chemical scavengers to prevent unwanted interactions, polymers that improve physical characteristics.

 

Prover developing is dependent on controlling the infusion rate. The gelatin emulsions swell when wet, this allows the chemicals of the process to enter and exit. Control of the infusion rate is a customized. A pre-soak affords unwanted changes to the infusion rate.

Modern color films are multi-coated –overcoat—UV filter coat—fast yellow—slow yellow—interlayer-fast magenta.....

Thanks for that Alan. A very detailed view of why a pre-bath isn't a good idea with colour film.

Thank you all. It seems that Bill and Alan have, more or less, come to a similar conclusion that the swelling of the emulsion layers have an effect on the rate of reaction of the development process. Initially, I would have thought the presence of water (swollen film) might lead to over-development if I think of film as a kitchen sponge. A very dry sponge takes a while to initially absorb water and to become saturated. So, I figured dry film might act similarly. However, seems like dry film is pretty hydroscopic so it will tend to suck in developer solution upon contact. In this case, if the film is already pre-saturated with water, then displacing the water with developer requires some time, which may lead to slightly less development..though...how much can it really be?

The simplest answer (the more complex answers might be better) is that the timing of the first chemical step assumes that the developer will need to soak into dry film, not film that is already wet. A presoak will allow the developer to diffuse faster. In B&W processing, wet film requires a shorter developer time but in color film, which has many layers, the development may be uneven through the layers if the film is already wet.

When I used to develop 8x10 inch Ektachrome sheet film, I would start with the developer temperature three degrees higher than the designated developer temperature of 101 deg F. I learned on my first attempt that putting six sheets of film at room temperature into 101deg developer instantly dropped the developer temperature down to 98 deg. F. resulting in magenta cast results. I later thought that I should have pre-soaked the film in 101 degree water to warm it up before putting it into the developer. From the above posts I guess that would not have been a good idea.

In this case, if the film is already pre-saturated with water, then displacing the water with developer requires some time, which may lead to slightly less development..though...how much can it really be?

 

Hi, like I said above, it's purely hypothetical on my part, but I expect that the difference would be fairly small, and probably not even noticed by most people. (You really need either a reference to compare against, or practical experience to know what could have been.)

 

My experience is mainly from a large studio chain where we would periodically run critical tests on film/paper materials under consideration for use (these were always the "professional" products intended for portrait work). These would include perhaps five models with different complexions and hair color, etc., over a wide range of exposures. Then we'd make a "best" reference print from a "normal" exposure, then everything would be hand-balanced for a close match. So we might end up with 50 or so 8x10" prints, plus maybe a half-dozen 16x20s laid out in a "color booth" for evaluation. We'd look critically at skin tone reproduction, from darkest shadows into highlights, looking for "color crosses," plus at color references, etc.

 

(A color cross is where color changes in conflicting directions with brightness change. For example, say we have a good skin color on most of the face, but the semi-specular highlight areas have a slight bluish tinge. Now, to "correct" that tinge you "remove" the blue by making the print more yellowish. But now the bulk of the skin color is too yellow. In other words this color problem is not correctable by normal means; the shadows vs highlights require different corrections.)

 

Now I would be virtually certain that we would be able to see significant differences in a film that is processed with a pre-soak. In fact, I'd probably be willing to bet nearly everything I own on it. But you can see how finicky we were about things, and we look at them side by side. But as I said, we never actually did a pre-soak test - cuz it's fundamentally a dumb thing to do with a replenished chemical system.

 

Now, if a more "regular person" were to process film using a pre-bath, perhaps photos from a car show or a family get-together, etc., and scan the film, or whatever, I'm very doubtful that they would see a problem. You might wonder if they are capable of seeing differences. I would say yes, most people, unless they specifically have some sort of color vision deficiency, CAN see this sort of difference. But it might need to be in side by side comparison to something better. Then the situation becomes, "oh, this one is much better!" If you point out, "earlier you thought this one was fine..." the response would probably be, "oh, that was before I saw the better one." In other words you don't know what you're missing; you don't miss what you never had.

 

Back to Kodak's recommendations, I've worked with Kodak materials and specs, etc., for a lot of years. I would say that Kodak's position has historically been to take a conservative position on their recommendations, meaning that they try to protect their customers from screwups. Consequently a lot of people will successfully stretch chemical usage beyond what Kodak recommends, or do things contrary to what Kodak says. They can mostly do this, because Kodak was conservative with the recs.

 

Anyway these are just my views. In the end, people mostly are gonna do what's"good enough" for them, for what they have to "pay."

I suspect that the timing for black and white developers should be different, but that it is close enough most of the time.

 

My old favorite developer is Diafine, which specifically says no presoak.

 

Diafine works by part A soaking into the emulsion, and then being activated in part B.

The exact amount of A soaked in determines how it develops.

 

I don't know if presoak would make developer diffuse faster (into the already wet emulsion)

or slower (while the water diffuses out).

 

In any case, C41 timing is designed without it.