Twist agitation - has anyone ever done tests?

[faberryman]

The last time I developed film in a group setting I noticed that all the students used somewhat different methods, timings, and patterns for agitating. Everyone's film came out without issue. Unless you are having a problem, I'd continue doing what you are doing. I have been using the same way of agitating for fifty years. I learned it from a friend who taught me how to develop film in high school. Who knows where he learned it. I don't know if it is the right way, but I have maintained a dogged consistency, and it has served me well. Sometimes I think we would be better off without YouTube where experts who aren't really experts tell you the correct way to do things which they probably learned from a friend too.

 

[AgX]

I think for twiddling to work, you'd have to do it continuously in one direction.

I think one aim of this thread is to validate this.

In favour of your stand speaks that the last Jobo tanks offering the twisting-feature got a kind of ratchet design allowing only clockwise twisting.

 

[Arvee]

There is high variability in person-to-person testing.

Excellent point! Technique can be a huge factor in the variability of results/observations cited on the internet. I hadn't considered this facet of the issue. To conduct a meaningful test, it definitely must incorporate a standardized technique.

 

[BrianShaw]

I wish you luck in getting actual sources of scientific evidence. Already all of the posters are giving you their experience of what has worked for them. This is all most of us can do.

If we were to respond strictly to what you have asked the answers would be short to the point of sounding abrupt

If you wish us to stick strictly to the terms of your request then it might help if you were to re-iterate exactly what your terms are

If you do, then expect short or no answers but if you do not wish the thread to end this way then fine, most of us will continue to respond in our usual way

pentaxuser

Excellent observation! I won’t bother responding because I wasn’t asked.

 

[BrianShaw]

I think one aim of this thread is to validate this.

In favour of your stand speaks that the last Jobo tanks offering the twisting-feature got a kind of ratchet design allowing only clockwise twisting.

I rotate slowly in both directions, back and forth two or three times for agitation at each minute. Works for me.

 

[Sirius Glass]

I rotate slowly in both directions, back and forth two or three times for agitation at each minute. Works for me.

That is similar to what the Jobo processor does.

 

[Helge]

I rotate slowly in both directions, back and forth two or three times for agitation at each minute. Works for me.

With that few rotations, the developer in the middle of the spiral would move very little.
You might get compensation if you have very generously exposed shots or you’re pulling. But otherwise I’d start carefully inspecting my negatives.

 

[Helge]

That is similar to what the Jobo processor does.

Might be wrong but isn’t Jobo always continuous agitation?
Anyhow in a Jobo film is only partly submerged. That makes a huge difference to laminar flow.

 

[BrianShaw]

With that few rotations, the developer in the middle of the spiral would move very little.
You might get compensation if you have very generously exposed shots or you’re pulling. But otherwise I’d start carefully inspecting my negatives.

Well. That is about 3-5 seconds of agitation at each minute. I can hear 'swishing' so I know the chemistry is moving. As I stated, no uneven effects observed.

 

[MattKing]

Sometimes, I twiddle vigorously and sometimes do the wobbly figure eight according to my whim.

I put on nitrile 'examination' gloves when I develop film.

And that is indeed one of the problems I've observed when only twiddling.

I think for twiddling to work, you'd have to do it continuously in one direction.

I rotate slowly in both directions, back and forth two or three times for agitation at each minute. Works for me.

It occurs to me that if someone who has no contextual knowledge should come upon this thread, they might have some very strange images come to mind!

 

[Sirius Glass]

It occurs to me that if someone who has no contextual knowledge should come upon this thread, they might have some very strange images come to mind!

Monitor going off topic and rogue at the same time, in coordination, together, simultaneously, at once!

 

[Craig]

I think it's a useful experiment to try twiddling in a Paterson tank with the lid off , so the motion of the liquid can be observed.

I do a vigorous twisting to get both the liquid and reel moving, then abruptly stop the reel. The liquid keeps moving and tumbles around the reel. It's definitely not laminar flow. Another large variable is how much liquid is in the tank. With the rotation, the liquid is flung toward the edge of the tank and the fluid level drops in the centre. I find if the tank is fairly full (such as when doing a 120 film) the liquid rises up to the lid and then falls over creating turbulence.

As with inversion, there are a number of variables than can affect outcome.

I was taught the "twiddle method" in school decades ago and it's worked well for me.

 

[Helge]

I think it's a useful experiment to try twiddling in a Paterson tank with the lid off , so the motion of the liquid can be observed.

I do a vigorous twisting to get both the liquid and reel moving, then abruptly stop the reel. The liquid keeps moving and tumbles around the reel. It's definitely not laminar flow. Another large variable is how much liquid is in the tank. With the rotation, the liquid is flung toward the edge of the tank and the fluid level drops in the centre. I find if the tank is fairly full (such as when doing a 120 film) the liquid rises up to the lid and then falls over creating turbulence.

As with inversion, there are a number of variables than can affect outcome.

I was taught the "twiddle method" in school decades ago and it's worked well for me.

Most things and processes come in degrees.
There is bound to be some degree of laminar flow in between the tight spiral of film.
If the spiral was moving up and down it would be less.

Which made me think of an old idea I had. How about pumping developer down through the center column where the stick goes?
It would be a matter of finding the right flow rate. Intake for the pump would just be next to the entering tube in the mouth of the funnel of the tank.

 

[Andrew O'Neill]

Nothing wrong with twiddle stick developing but... be gentle, especially when processing 35mm film. I got awful surge marks between the sprocket holes when I first processed film years ago. Realised it was because I was treating that little stick like a roulette wheel.

 

[Craig]

There is bound to be some degree of laminar flow in between the tight spiral of film.

Depends on the Reynolds Number!

 

[Helge]

Depends on the Reynolds Number!

It’s basically water so that’s easy. With a two to three millimeter distance between layers, yes there is.

 

[ozphoto]

I do both and see no difference with 35mm films. The key is to not twiddle to fast.

Agree with this 100%. I've been using the "twiddle" method for over 30 years (and have also undertaken the inversion method as well) - have never seen a difference. Admittedly, I'm not concerned with the science, so I have never measured my negs with a densitometer; for me, achieving consistent, correctly developed negatives and consistent prints on my paper, and grade of choice, are what I'm after.

It should be noted though, that I did do some thorough testing on my developer and films of choice when I first started out - for many years this was Agfa's superb Atomal FF, and I tested the complete B&W Agfa range, as well as Kodak's TriX, PX125, and their TMax range and Ilford's original FP4 and HP5. When Agfa's film division shut up shop, I eventually moved to D76 and Rodinal, depending on availability and where I was based. Both of these have performed just as well - I can't discern any difference at all

I also use the method for 120 negs and these too have never shown uneven development. As @Eric Rose points out, the speed at which the negs are "twiddled" is the most important factor, get that right (along with the correct developer) and I'm confident you won't face any issues.

All I can suggest is, test, test, test; burn a couple of short rolls of your favourite film and developer combo, run the first lot using the twiddle stick method and the second using the inversion method. Once dry, have a good look at the negs and see if you have any issues (if so inclined check with a densitometer too) - if what you get is acceptable on both fronts, choose how you wish to continue developing and stick with it. IMHO, continuously changing from one developer to another and back (along with your processing method) isn't conducive to consistent results, often ending in disaster or disappointment; instead, make those changes because you want to investigate new combinations (or change your developer of choice completely) and be sure to once again, test, test, test.

 

[koraks]

How about pumping developer down through the center column where the stick goes?

Wouldn't it be more straightforward to just use inert gas agitation as several people in the large format arena do? Pump something like CO2 into the bottom of the tank. There won't be any laminar flow and lots of turbulence. A suitable perforated plenum might be installed in the bottom of the tank; there's usually plenty of room for this if the developer volume is expanded only a little bit to account for the reel sitting a bit higher.

Of course, either of these pumping solutions (no pun intended...) are way more complex than just picking up the tank once in a while and turning it, or just throwing it onto a rotary processor and wait until it's all done. That's probably why I never bothered seriously looking into it. I can see the usefulness for large format shooters who for some reason intend to stick with x-ray film, particularly the double sided kind. The only way I'd imagine you can get even development from that stuff is in a hanger-and-tank setup with gas burst agitation.

 

[Craig]

Wouldn't it be more straightforward to just use inert gas agitation as several people in the large format arena do?

I think the problem with that for roll film on reels is that the introduced gas will likely trap bubbles within the reel, causing uneven development and air bells. That's not a concern for sheet film on hangars in a deep tank.

 

[AgX]

Wouldn't it be more straightforward to just use inert gas agitation as several people in the large format arena do? Pump something like CO2 into the bottom of the tank.

CO2 is NOT a inert gas.

 

[koraks]

@Craig I doubt that's a problem with sufficient burst frequency.

@AgX, duly noted and correct, but given the buffering of typical developers it won't present problems I'm sure. Argon would be better and way more expensive.

 

[AgX]

Good point with the buffer, but why stressing the buffer in addition.

 

[foc]

If you want to use a gas burst in the developer (deep tank) then why not use nitrogen, like in C41rack & tank processing.

 

[Arvee]

Since I posted, I have been scouring the web (again!) for information and found one case that had conducted rudimentary tests using a densitometer and reported a noticeable difference in density between frame 1 and frame 36. Also, I sort of recorded comments in my head whether the person noted a difference or no difference. Those who noted a difference said it was end to end where I only found one comment that the person saw an edge to edge difference. In a very crude analysis, I felt the split was about half and half; half encountered issues and the other half had no issues; issues of end to end variation in density.
This led me to believe that technique may be a much larger factor than originally anticipated. Perhaps those who experienced problems twirled gently/cautiously which would reduce the amount of turbulence seen at the center of the spiral vs the outer rim. This is true regardless of how vigorous the agitation technique.
Perhaps those who agitated more aggressively would see ample turbulence at the center to satisfy the diffusion process. but more turbulence at the outer rim than needed to fulfil the diffusion process. This presumption is based on the assumption that the diffusion process occurs at a linear rate independent of the degree of turbulence in the laminar layer and would explain why some folks have problems with uneven densities where others see none.
Which begs the question: does anyone out there have intimate knowledge of the diffusion process and is it a linear function or a second or third order function? I am unable to find anything on the net in this regard.
With my limited knowledge of physics, I intuited that the diffusion process is a steady linear function as developer migrates through the layers of the emulsion and controlling the rate of fresh developer reaching the emulsion.
If my assumptions are valid, this would explain why twist agitation works well for some and not for others. The subjective nature of technique is creating the variability in the amount of fresh developer is reaching the emulsion.

Again, anyone have intimate knowledge of the rate of the diffusion process? I really would like to know! I seem to recall Mr. Koch sharing information about the process a while back. Gerald?

And, again, thanks for the many replies; they are aiding my limited understanding of the agitation process.

 

[Sirius Glass]

Since I posted, I have been scouring the web (again!) for information and found one case that had conducted rudimentary tests using a densitometer and reported a noticeable difference in density between frame 1 and frame 36. Also, I sort of recorded comments in my head whether the person noted a difference or no difference. Those who noted a difference said it was end to end where I only found one comment that the person saw an edge to edge difference. In a very crude analysis, I felt the split was about half and half; half encountered issues and the other half had no issues; issues of end to end variation in density.
This led me to believe that technique may be a much larger factor than originally anticipated. Perhaps those who experienced problems twirled gently/cautiously which would reduce the amount of turbulence seen at the center of the spiral vs the outer rim. This is true regardless of how vigorous the agitation technique.
Perhaps those who agitated more aggressively would see ample turbulence at the center to satisfy the diffusion process. but more turbulence at the outer rim than needed to fulfil the diffusion process. This presumption is based on the assumption that the diffusion process occurs at a linear rate independent of the degree of turbulence in the laminar layer and would explain why some folks have problems with uneven densities where others see none.
Which begs the question: does anyone out there have intimate knowledge of the diffusion process and is it a linear function or a second or third order function? I am unable to find anything on the net in this regard.
With my limited knowledge of physics, I intuited that the diffusion process is a steady linear function as developer migrates through the layers of the emulsion and controlling the rate of fresh developer reaching the emulsion.
If my assumptions are valid, this would explain why twist agitation works well for some and not for others. The subjective nature of technique is creating the variability in the amount of fresh developer is reaching the emulsion.

Again, anyone have intimate knowledge of the rate of the diffusion process? I really would like to know! I seem to recall Mr. Koch sharing information about the process a while back. Gerald?

And, again, thanks for the many replies; they are aiding my limited understanding of the agitation process.

In short, this agrees with my expericence with twist agitation: too little or too much causes development problems, what is in between works well.