Airbell Experiment

[markbarendt]

A capped container filled with liquid will allow no circulation. Therefore, agitation results in nearly zero exchange of chemicals. There must be some movement of the liquid and / or the reel to accomplish this.

PE

Ok so I just went into the kitchen to test this. Grabbed a glass Ball canning jar filled it completely with water and added a small pinch of used coffee grinds and capped it. One rotation and the entire contents was the color of tea and uniform. Dumped and there were some grinds left in the bottom, refilled and capped again. One shake and they were randomly dispersed.

Rotating the jar around any axis showed the grinds changing position relative to the jar, the shape of the jar also seems to provide a fair amount of turbulence when not rotated around the normal vertical axis.

I would assume the chemicals we use would act no different and that the film reel would add even more turbulence.

What am I missing?

 

[Arvee]

I don't even attempt to explain it; it's a red herring.

The root cause of this problem is Acros. Different developers produce varying degrees of foaming, regardless of which film they're acting on. There's an inherent characteristic of Acros which prevents those foam bubbles, however numerous, from leaving its surface when gravity is the only force motivating them to do so. With 35mm Acros, the "latched" bubbles end up in the sprocket area, so there's no real problem. With 120 Acros, no matter the measures taken, one can minimize but never completely eliminate bubble-caused circular underdeveloped spots.

In rotary agitation, where motion is mechanically driven, the bubbles are continuously dislodged from Acros' surface and don't cause an issue. I've never achieved satisfactorily (to me) even development of 120 black and white negatives using a Jobo processor; I've tried Jobo 1500 and 2500 reels/tanks as well as the Jobo/Hewes 1500 reel, using both a CPE2+ and CPA/CPP2+. Therefore, I only process 120 film (never Acros) using inversion agitation in small tanks.

Acros has several unique characteristics, including its spectral sensitivity and freedom from reciprocity failure. The way I use it is in its 4x5 form, developing the sheets in Jobo Expert drums. Perfectly even results with no air bell defects.

With all due respect, Sal, I remain unconvinced. I shoot Acros 120 exclusively and develop in D76, Xtol and Rodinal. I have never had air bell. I must be the exception to your rule.

 

[Sal Santamaura]

...I shoot Acros 120 exclusively and develop in D76, Xtol and Rodinal. I have never had air bell...

Perhaps the OP and I, both near sea level, don't have the advantage of lower ambient air pressure that you do high in the mountains. That might be what it takes for the air bells to pop, despite Acros' propensity for hanging onto them.

 

[Peltigera]

Ok so I just went into the kitchen to test this. Grabbed a glass Ball canning jar filled it completely with water and added a small pinch of used coffee grinds and capped it. One rotation and the entire contents was the color of tea and uniform. Dumped and there were some grinds left in the bottom, refilled and capped again. One shake and they were randomly dispersed.

Rotating the jar around any axis showed the grinds changing position relative to the jar, the shape of the jar also seems to provide a fair amount of turbulence when not rotated around the normal vertical axis.

I would assume the chemicals we use would act no different and that the film reel would add even more turbulence.

What am I missing?

What you are missing is that the coffee grounds are not dissolved and they are denser than the water. Invert the canning jar and the grounds will move through the water because they are denser. That does not occur in developing - all the ingredients are dissolved and the developer solution is homogeneous. This means that no part of the developer is denser and nothing will move when you invert the container

 

[DWThomas]

Hmmm -- over the last few years I've developed approximately 50 rolls of Acros in HC110 1+63 and have not been seeing this problem.
I do one-shot, mixed with distilled water.
I do NOT pre-wet the film.
I use 425 mL in a typical stainless steel tank, which brings the developer about a 1/4 inch above the reel but leaves air space -- I found development more even than with the tank full.
For the first 30 seconds, I do inversions at about one every two seconds or so, thumping the tank on a firm wood block after each. I also (in general) rotate the tank about 120º around its vertical axis between each inversion to spread the motion around.
After the initial 30 seconds, I do five inversions (in about six to so seconds) at each minute. I usually do a couple of thumps at the one minute mark, but after that don't bother.
I use a Hewes reel; I wash the film on the reel, but do NOT put the reel in PhotoFlo (see-saw film, on clips, thru a plastic container).

What can I say?!

 

[DWThomas]

This means that no part of the developer is denser and nothing will move when you invert the container

But agitation will occur -- yes the liquid tends (but far from perfectly) to stay stationary, but the twisting of the tank is moving the reel and the film (and the tank) relative to the developer and that's all we need to accomplish.

 

[Peltigera]

That would depend on the spirals being fairly loose in the tank. With my rather old Paterson tanks I would not want to rely on the very minimal movement of the spirals to achieve sufficient agitation.

Sent from my A1-840 using Tapatalk

 

[Arvee]

Ok so I just went into the kitchen to test this. Grabbed a glass Ball canning jar filled it completely with water and added a small pinch of used coffee grinds and capped it. One rotation and the entire contents was the color of tea and uniform. Dumped and there were some grinds left in the bottom, refilled and capped again. One shake and they were randomly dispersed.

Rotating the jar around any axis showed the grinds changing position relative to the jar, the shape of the jar also seems to provide a fair amount of turbulence when not rotated around the normal vertical axis.

I would assume the chemicals we use would act no different and that the film reel would add even more turbulence.

What am I missing?

Mark, repeat your test with a drop or two of food coloring. This is much closer to the real life situation.

 

[markbarendt]

What you are missing is that the coffee grounds are not dissolved and they are denser than the water. Invert the canning jar and the grounds will move through the water because they are denser. That does not occur in developing - all the ingredients are dissolved and the developer solution is homogeneous. This means that no part of the developer is denser and nothing will move when you invert the container

I fully agree that the grounds will sink but for a low tech test they do provide a very reasonable visual aid.

If there were little or no motion/turbulance in the water as the jar was inverted the grounds would not disperse easily from their place at the bottom of the jar. One inversion cycle dispersed them nicely.

The place I can see no airspace as a problem is with "sloshing" agitation.

The place I can see an airspace as an advantage is with constant rotation, where crossing the boundaries from air to fluid would mechanically eliminate bubbles.

What I don't see yet is any advantage to an airspace when inversion is in involved.

Inertia dictates that the liquid is going to try and "stay put" unless acted on by an outside force and our hands are forcing the film and reels to move through the liquid for roughly 180 degrees, the drag and shape of the container should start moving the liquid some but its not a gel or solid that will follow exactly, then we reverse the rotation for 180.

With film and reels that's a lot of turbulence in the tank, how can that possibly leave the fluid unaffected/undisturbed?

 

[markbarendt]

Mark, repeat your test with a drop or two of food coloring. This is much closer to the real life situation.

That's essentially what my first unwashed pinch of coffee grounds showed. One inversion cycle to full dispersion of the "fines" which did not drop out of solution. Once uniformly mixed, the size of the fines/the coloring particles, makes observation of their motion problematic.

 

[markbarendt]

That would depend on the spirals being fairly loose in the tank. With my rather old Paterson tanks I would not want to rely on the very minimal movement of the spirals to achieve sufficient agitation.

Sent from my A1-840 using Tapatalk

The spiral doesn't have to "move" in relation to the tank, they move in relation to the fluid in the tank. Inversion and inertia take care of that.

Stick your hand in some water, twist it 180 degrees, did the water flow around your fingers? Was the water disturbed/did it move? Did the water try and stay where it started? Was the water mixed as you twisted your hand? Is it likely that any single water molecule is where it started in relation to your hand?

 

[Photo Engineer]

The coffee grounds are not a good test for this. Consider that the developer must move in a fluid motion over the surface of the film to dislodge any old chemistry (or bubbles) and must then exchange those old chemicals for new ones. These chemicals are all nearly at the density of each other in solution and therefore agitation, good agitation is the means for exchange.

If it were easy to move things in this fluid environment, we would have no such thing as bromide drag which is caused by bad agitation.

If the film being used in a test shows processing flaws as well as air bubbles, this process has multiple flaws in it and all of the coffee ground tests are flawed as well just due to design. This is not a simple problem. It is one that EK and others have investigated in depth for years.

PE

 

[markbarendt]

PE

I can definitely see that having an air space can facilitate more easily mixing and more redistribution of the chemicals. The bubble actually acting like an agitator as the tank tumbles but what I'm not buying into is the thought that inertia disappears and that the liquid in a capped tank starts acting like a gel.

If that were true it would be really tough to get a brand new bottle of WishBone Italian salad dressing to mix, no?

 

[Photo Engineer]

Mark, it does not act like a gel.

If you look at a drop of dye solution placed into water you will see slow movement of the dye in a cloud as it disperses into the larger volume of fluid. If you stir, the cloud vanishes more rapidly. This stirring is agitation.

Now imagine old chemicals, old halide (Br and I) and bubbles at the surface of the film in a layer on top and within that film. You want to exchange all of that for fresh solution and no bubbles. Imagine them trying to move away on their own and then with mild movement of the film, and then with heavy movement with "banging" of the container. These are 3 scenarios that must be envisioned as happening with no, poor and good agitation. There is a fourth which is over agitation.

The optimum produces no problems! All of the others introduce faults deriving from this.

Now, as for Wishbone salad dressing, imagine you have their Italian and Caesar (or other separated type) dressing side by side. Turn them both upside down and you see that the thicker one does not mix well, but the Italian does seem to mix. You have to shake both to mix them. However, since this is oil and water it is a reach to compare it to an all water system.

PE

 

[winger]

Perhaps the OP and I, both near sea level, don't have the advantage of lower ambient air pressure that you do high in the mountains. That might be what it takes for the air bells to pop, despite Acros' propensity for hanging onto them.

I live about an hour or so from OP and have never gotten airbells with Acros. I think we're likely at a similar elevation, even as hilly as it is around here. I've used Ilfosol S, Ilfosol 3 (which I wasn't as happy with because of short developing times) and now DDX. Hewes reel in a stainless tank with 450ml and "standard" agitation, no prewet.

I manage to find other ways to mess up, but I've only gotten airbells on a sheet of 4x5 that I know I didn't agitate well or tap sufficiently (HP Combiplan).

FWIW, I prefer stainless for 120 and I can rap the tank fairly solidly, knowing it isn't likely to crack. I do 3 thunks after each agitation with the tank tilted and I do them with the tilt slightly changed each time. After the initial agitation, I think I do more thunks, though (it's been awhile since I developed and I have a backlog sitting here). Some of muscle memory and I have to do it to remember how I do it. Agitation is by inversion.

 

[Truzi]

markbarendt,
Although the-coffee ground example shows there is movement, it does not speak to whether that movement is adequate enough for the purpose (the food-coloring would be a better example). I would think both thoroughness and speed of the mixing would be a factor.

 

[bvy]

I strongly suggest that, in order to maintain your sanity, you either use a rotary processor or a different brand of roll film. Inversion agitation of 120 Acros is, in my opinion, impossible to accomplish without some minimum number of air bells, regardless of developer or reel type used. I've tried them all, including Paterson, Kindermann and Hewes tanks/reels as well as Perceptol, Ilfotec HC and ID-11. Even two pre-rinses in sequence won't eliminate the spots. Also, that collection of air bells at the top is what keeps things less developed there, not any lack of developer. Paraphrasing the bumper sticker that I liked best among all those observed while commuting 100 miles per day round trip for 33 years:

"You'll feel much better when you give up hope."​

Touche. You win. I'm moving to XTOL and rotary processing.

 

[MattKing]

Touche. You win. I'm moving to XTOL and rotary processing.

Just to frustrate you a bit, I do successfully use continuous rotary agitation for the first 30 seconds of development, with inversion agitation thereafter.

And as you may recall, I use a 3 minute pre-rinse as well.