Some thoughts on seasoning and steady state

I have been reading several threads lately that discuss replenishment and several older threads stick in my mind that covered steady state seasoning and replenishment.

It seems that there is a great misunderstanding over the situation with both seasoned developers and with the steady state of seasoned developers.

First off, let me state that I fully understand that by many definitions, steady state excludes startup and shutdown of a given process. Now, understand this. If, in photography, steady state did not include startup and shutdown, a lot of customer’s films would be ruined every time a photo lab charged their machine(s) with new developers. The startup in a photo process must yield the same results as the seasoned one as closely as is possible.

In the case of D-76, it is achieved by D-76 as startup and D-76R as replenisher. Each of these have different formulations and used separately would yield different results. Used properly, they will give you a constant result from startup to shutdown thus giving the effect of a steady state condition. The tank developer does not resemble either the fresh developer or the replenisher (see below).

In other words, fresh D-76 and replenished seasoned D-76 should give close to the same results. I know that there are some differences, but this is due to unavoidable leaching of development byproducts and chemistry into the developer by the wide range of films being put through the process and which cannot be perfectly compensated for due to the variety of films one may use.

In the final analysis, the steady state may yield the same characteristic curve, sharpness, speed and grain as the fresh developer, but it does it by a slightly different chemical composition. So, for example, the final seasoned D-76 in the tank contains Iodide and Bromide and neither the startup developer nor the replenisher did. But, the seasoned developer also has a different blend of HQ, Metol and alkali. This balance is changed to reflect not a steady state in chemical analysis necessarily, but rather, as closely as possible, it represents a steady state in the film’s characteristics when processed in the ever changing developer. In other words, the film’s steady state remains constant from startup through equilibrium and no customer film is lost even though the chemistry in the tank is undergoing a change from startup to steady state or equilibrium.

Even some excellent engineers and chemists seem to miss this point. Since it is not a generally published topic, nor is the condition easy to analyze for, it is often misinterpreted or overlooked. I thought I might shed some light on it.

So, steady state can refer to the condition of the developer solution composition, or to the state of the results obtained from the process, or both. In photography it mainly refers to the results obtained. And, in so doing, it must encompass the startup and continuous running or we would be ruining a lot of customer film in photo labs. I think that you can see that what I have described above is obvious.

A photofinisher cannot run blank film through his process to season a fresh tank of developer. It is not cost effective. The developer must be right at startup. The same goes for us when we mix up new developer. We must not be required to season that developer. It must be at a steady state at startup to yield the proper results.

I hope I have clarified things for some people.

PE

 

Ian;

I did say it was not exact, but the alternative is a very large difference between fresh and seasoned. There is no huge difference. The actual differences are very tiny or customers would reject their film as being misprocessed. I think you can agree to that.

PE

 

I think you will find that the average user can usually not spot the difference. Or, that the difference is not important enough to comment on, and that is my point. The developer varies quite a bit as it seasons and is replenished, but the final result varies hardly at all. And, the variation is not important to the average user.

PE

 

Well, you can use any method you want, the basic system is designed to work with batch replenishment or by using flow meters. As for the variations between fresh and seasoned, it is there, but in terms of quality, it is minor. After all, fresh and seasoned color processes work just fine except for a tiny shift in color balance in some cases. I think that even this has been worked out in recent years.

At Cape Canaveral we ran thousands of feet of MP film a month and did not have to "run in" fresh developer before quality was up to release standards. In the lab I worked in in college, we did not run in. And, at Kodak we worked with fresh developer and measured release standards, while the release technicians worked with seasoned developers. Our data were comparable in terms of all release characteristics within tolerances.

PE

 

If there was a significant difference, I think that the manufacurers would be moved by the commercial and professional photographers to publish this fact and the data. As is, they support one "aim" from each developer and do not mention the seasoned state for the most part.

I think that Fotch has a point that cannot be dismissed. Many of the "well known" sources are years old and many had single tests, that they said were lower in quality. They did no have side-by-side adjusted comparisons.

PE

 

Sandy;

There is a fairly big operation in NYC that does a lot of custom B&W. It is called SixtyeightDegrees. Another is an APUG sponsor doing custom B&W work. So, this is by no means a vanished type of process.

PE

 

This is a very important statement. My reply is rather easy though.

1. D-76 is old, but in spite of that replenishsment with it still works by giving the same (or virtually the same, depending on POV) observed results with modern films and with old type films in spite of the differences in chemistry. In fact, that caveat in prens above may be due more to the mixes of film in commercial operations than for any other reason. I might add that many other developers do as well or better. XTOL does the job by being its own replenisher, and that is the result of a modern formulations with modern films. So, this addresses one point.

2. Your comment seems to feel I am suggesting replenishment, but in fact, I was answering some threads and posts here and elsewhere, and also some e-mails and PMs which indicated to me that there were some people who did not understand the way the replenishment process worked. I am not advocating that anyone change. If it works, use it!

PE