Concentration or amounts of developer?

[psmithp]

• A roll of 120 film and one of 135-36 film (of the same type) have roughly the same surface, amount of silver bromide, etc.
• If I develop a 120 roll in 0.6 l of developer and a 135 in 0.3 l of the same developer, I need the same development times.
• When the 135 roll is developed, the developer is exhausted.
• As the 120 roll has the same surface and I use twice the amount of developer, half of the developing oomph must still be there after the prescribed development time, and the average concentration during development is much higher.

But nobody ever suggests reusing the 120 developer. Can anybody explain this apparent paradox to me?

 

[Nitroplait]

You are talking about one-shot development. You probably can reuse in said scenario but the development (time) will be different when reused - and probably also the quality of the result.

 

[psmithp]

I still wonder why development times are the same...

 

[pentaxuser]

My understanding is that if you have developed in stock solution, that is no dilution such as 1+1 , you can probably use use the developer again for both 35mm film and 120. In the case of the same developer you might not need to change the development time for the second film. In theory and following your logical argument above your 120 film which has twice the stock developer for the same surface might not require any change to development time for the second film and in theory the 35mm fílm might need to be developed longer but not the 120 as there is extra capacity there which may not be there for the 35mm film. My guess is and this is only a guess, the same development time for the second film in both 35mm and 120 examples may still be fine for making prints Would a densitometer reveal under-development? Maybe but it may hardly be noticeable

I have no idea why no-one ever talks about re-using the developer for 120 and in fact is it the case that no-one ever talks about re-using developer for 120 film?

pentaxuser

 

[pentaxuser]

I still wonder why development times are the same...

Well both fílms need a the same set time to develop the film to the correct level but as you have said and I agree, there is, in effect. excess developer there for the 120 surface area but it has to be there to ensure that the 120 is fully covered by the liquid.

Thinkíng aloud now for the sake of discussion on this, it seems to me that if there were a way to ensure that a 120 film could be covered by the same smaller quantity of liquid as is needed for 35mm film then you could effectively develop a 120 film in the smaller amount needed for 35mm film

pentaxuser

 

[bedrof]

• A roll of 120 film and one of 135-36 film (of the same type) have roughly the same surface, amount of silver bromide, etc.
• If I develop a 120 roll in 0.6 l of developer and a 135 in 0.3 l of the same developer, I need the same development times.
• When the 135 roll is developed, the developer is exhausted.
• As the 120 roll has the same surface and I use twice the amount of developer, half of the developing oomph must still be there after the prescribed development time, and the average concentration during development is much higher.

But nobody ever suggests reusing the 120 developer. Can anybody explain this apparent paradox to me?

If you dilute developer from the concentrate to fit 0.3 or 0.6 liters of working solution and you keep the same ratio, so you got the same strength solutions and you can run a 135 in 0.6 l and develop for the same time.
If you're speaking about a reusable solution, than no matter what you develop in it you change the contents slightly, but such developers were formulated so to neutralize the negative effects to some extent.

 

[Alex Benjamin]

As the 120 roll has the same surface and I use twice the amount of developer, half of the developing oomph must still be there after the prescribed development time, and the average concentration during development is much higher.

Part of the flaw in your logic comes from believing there is such as thing as "developing oomph" and that it can be precisely divided in half. Film development is a two-way chemical process, It's not only the film that is affected, but also the developer. For example, during the development, oxidation takes place, and the entire developer is affected. Doubling the amount of developer used doesn't change that.

There are other chemical processes that take place, but, also, there are many factors that influence rate of development— and, hence, exhaustion —, such as temperature, dilution, and agitation. Quantity of developing solution is not one of them, in the sense that putting more of the developing solution but with the same dilution, same temperature, same agitation will have little effect on the rate of development of the complete solution (unless, of course, you're talking about much larger differences of ratio in volume than 1 to 2).

Not to mention that rate of development is also affected by the density of the latent image itself. A negative with lots of highlights will not exhaust the developer the same way as a negative will mostly shadows.

Is your complete solution less affected by the various chemical processes at work if you double the volume? Perhaps. By how much? Impossible to tell withouth a whole bunch of highly scientific testing.

 

[loccdor]

The developing times are the same because the developer concentration is the same.

The developer is generally not completely exhausted after developing a 135 film. You would have to be using a very weak dilution for that to happen. Beyond the safety margins of what manufacturers would recommend.

People don't reuse one-shots because the result can be difficult to predict. Many of them also decay quickly with time once diluted. You would need to run an experiment using a specific film and a specific time after 1st development to do the 2nd development. Oxidization rates based on the amount of air getting into your developer may also play a role. Not only would it be a lot of testing, it would only work for a very specific process where you did everything the exact same every time.

In short and as others have said - too many variables - developer is cheaper than film, cameras, and the time and energy spent to take good photos.

 

[Ulrich Drolshagen]

I usually put two rolls of 120 on one spool therefore developing them at the same time.

 

[koraks]

When the 135 roll is developed, the developer is exhausted.

It probably isn't, and if it is, it's only partly due to surface area developed.

Film development is a two-way chemical process, It's not only the film that is affected, but also the developer. For example, during the development, oxidation takes place, and the entire developer is affected.

Indeed, at the same time, halides (bromide & co) dissolve in the developer and as they act as restrainers, they also affect the working properties of the developer. As to oxidation, this occurs as a result of actual development activity (i.e. reducing silver), but also as the developer is oxidized by oxygen that's dissolved in the developer, which in turn is influenced by agitation and tank geometry.

How all this balances out is kind of hard to predict.

As the 120 roll has the same surface and I use twice the amount of developer, half of the developing oomph must still be there after the prescribed development time, and the average concentration during development is much higher.

Well, not 'much' higher since most developers aren't used to the point of exhaustion. We could say something like 'significantly' to 'marginally' higher depending on developer formulation.

 

[MattKing]

• As the 120 roll has the same surface and I use twice the amount of developer, half of the developing oomph must still be there after the prescribed development time, and the average concentration during development is much higher.

But nobody ever suggests reusing the 120 developer. Can anybody explain this apparent paradox to me?

I use developer in a replenishment scheme, so I always reuse the developer after developing 120 film.
@pentaxuser has it right. The only reason you have to use twice as much fresh developer for the 120 roll of film is because the amount of developer that covers a 135 film isn't enough to cover the 120. It is a question of physical geometry, not chemical capacity.
Outside of a replenishment regime, lots of developers, in various concentrations can be re-used in different amounts until exhausted.
But doing so adds complexity, increases the chance of error, and sometimes reduces quality.
So in order to ensure high, consistent quality, many people prefer to use developer one-shot, even if that doesn't maximize economy.

 

[Fatih Ayoglu]

Or you can put 2 rolls of 120 film on a single reel and develop that way. By this you will not waste any developer of that is what you are looking for

 

[pentaxuser]

We may not appear to have answered one of his questions about why he has not heard of anyone talking about re-using developer for 120 film. All I could say it that I wasn't aware that no-one talked about it but thinking about it my recollection is that the subject of re-using developer has been mentioned but only rarely in terms of 35mm and I cannot recall anyone mentioning it in terms of 120

Maybe everyone who has at least 2 x120s to develop uses tanks that do two together or attaches the second 120 onto the first roll and does it on the same reel? That certainly would seem to be the most economical and safest way

pentaxuser