Agitation question

[Photo_Smith]

Air Bells (bubbles)
My 2¢ are that some of the issues with bubbles may be due to the reels not being cleaned leaving wetting agent residue which in turn causes 'froth'.
Plain water pre-wet can be a good idea as water will cause the emulsion to swell and enable faster diffusion to take place when developer is added.
Some developers can also 'foam' due to a detergent effect of some constituents (borax, boric acid, sodium borate all have this detergent effect) ; E-6 colour developers are particularly prone to this so commercial labs put 'de-foamer' at the top of their tanks to combat this.

Agitation
The primary purpose for agitation is to ensure that the developer that enters into gelatin layer is kept at a similar p.h and concentration to the main body of the developing solution which is depleted by developing actions and can be also retarded by products of the development process such as Bromide.
Different films accept developer agents at different rates. The diffusion rate is critical for the first 30 seconds, especially with hardened gelatin types; the sort that are used in most T-grain and colour emulsions.
Agitation also builds density, the theoretical limit being about twice the density of non agitated material.
So the amount needed can vary depending on how vigourous the developing agent is and the diffusion rate of individual emulsions—some experimentation may be needed; manufacturers guides are a good start point.

 

[Austerby]

I habitually tap the tank after I've completed the agitation, usually by knocking the side of the tank against the counter's edge - as my developing tank is showing damage at the base from over-enthusiastic banging down when young (I've been using the same Paterson tank since the mid-1980s). I've no idea whether there's any point to the tap on the side but it's ingrained into muscle memory by now.

 

[V-12]

Highlight: very true, but froth-bubbles shouldn't stick to wet film, and unless they're stuck to the film, they'll rise pretty fast anyway.

You can agitate perfectly satisfactorily with swirl only, or by moving the film up and down in a deep tank: I've done both.

Cheers,

R.

Froth bubbles shouldn't stick to film Roger, they accumulate at the edges of the reel and remain trapped, causing uneven development along the 'top' edge of the film. If the developer is very frothy, if you haven't rinsed off photoflo from a previous session for example, the build up of bubbles can become quite deep. Having used deep tanks both as a student and commercially I agree that it is almost impossible to get air trapped on the reels.

 

[zauhar]

Dear Randy,

What leads you to say you were over-agitating before? I'm not arguing with your approach -- the whole thing is intensely personal -- but I'd be interested in the reasons for your decision.

Cheers,

R.

Roger, especially in the case of long development times, the highlights seem too saturated. I like high contrast, but I was clearly losing detail. With less agitation there is distinct improvement .

Randy

 

[john_s]

.....However, is there any sense in pre-wetting the film before adding the developer, to prevent these initial bubbles from sticking?

I've been developing 35mm film for many years and, apart from my first effort, had not had an air bell problem until recently when I started to use 120 size film. No matter what I did, I got some faint disks of underdevelopment on some frames, noticeable only in clear skies. Then I started to pre-rinse film in the tank for a couple of minutes and the problem went away. I still don't understand why I got this problem, but that's what I did to cure it.

 

[Roger Hicks]

Air Bells (bubbles)
My 2¢ are that some of the issues with bubbles may be due to the reels not being cleaned leaving wetting agent residue which in turn causes 'froth'.
Plain water pre-wet can be a good idea as water will cause the emulsion to swell and enable faster diffusion to take place when developer is added.
Some developers can also 'foam' due to a detergent effect of some constituents (borax, boric acid, sodium borate all have this detergent effect) ; E-6 colour developers are particularly prone to this so commercial labs put 'de-foamer' at the top of their tanks to combat this.

Agitation
The primary purpose for agitation is to ensure that the developer that enters into gelatin layer is kept at a similar p.h and concentration to the main body of the developing solution which is depleted by developing actions and can be also retarded by products of the development process such as Bromide.
Different films accept developer agents at different rates. The diffusion rate is critical for the first 30 seconds, especially with hardened gelatin types; the sort that are used in most T-grain and colour emulsions.
Agitation also builds density, the theoretical limit being about twice the density of non agitated material.
So the amount needed can vary depending on how vigourous the developing agent is and the diffusion rate of individual emulsions—some experimentation may be needed; manufacturers guides are a good start point.

Thanks for all these thoughts. I am intrigued by 'agitation' vs 'no agitation'. Presumably you're talking about developing sheet film in trays? Agitating by brush? As soon as there's adequate agitation (i.e. enough not to cause uneven development), then are variations in agitation not fairly trivial, and easily compensated for by changes in time? At least as far as overall density and contrast go, though not acutance and toe speed?

Surely all films today are hardened? That appeared to be one of the changes to Tri-X in its last iteration: the addition of on-line hardening.

For other readers: something that cannot be emphasized enough is the highlight, that they are starting points. All too many beginners -- I was among them -- assume that manufacturers' dev times are Holy Writ.

Cheers,

R.

 

[Photo_Smith]

Thanks for all these thoughts. I am intrigued by 'agitation' vs 'no agitation'. Presumably you're talking about developing sheet film in trays? Agitating by brush? As soon as there's adequate agitation (i.e. enough not to cause uneven development), then are variations in agitation not fairly trivial, and easily compensated for by changes in time? At least as far as overall density and contrast go, though not acutance and toe speed?
.

The test where they ascertained that agitation had a limit of doubling the density was done with brush agitation on a movie film with D16 (I think) by Kodak research.
I have the paper and the resulting curves somewhere if you want me to post?

Surely all films today are hardened? That appeared to be one of the changes to Tri-X in its last iteration: the addition of on-line hardening.

Cheers,
R.

Most emulsions are hardened but not all are hardened to the same degree. Different films have different gelatin types and properties; T-grains are normally harder than conventional films although it can vary between different brands.

Some films like the old EFKE/Adox and Foma films certainly have softer emulsions than Kodak and Ilford; softer spongier emulsions have higher diffusion rates making them better a getting developer into the emulsion.

The downside is less mechanical rigidity so they can be more susceptible to auto processor damage and pinholes and normally don't like rapid changes in temperature.

As far as I know all Kodak B&W products use the same gelatin.

 

[Moss1310]

Many thanks to everyone for the discussion! I have learned a lot from this and will reference some of the links and books listed as well.

 

[Roger Hicks]

The test where they ascertained that agitation had a limit of doubling the density was done with brush agitation on a movie film with D16 (I think) by Kodak research.
I have the paper and the resulting curves somewhere if you want me to post? . . .

I'd be very grateful if you could, without putting yourself to too much trouble.

Cheers,

R.

 

[John Bragg]

I always think of agitation as the third aspect or third tool in the box. Expose for the shadows, develop for the mid tones and agitate for the highlights. It is just another way to influence the final image. For me less is more. Dilute developer and hardly any agitation and for others continuous with a jobo processor or suchlike does the trick. I like the detail and texture in high values and try to keep them. Contrast can always be added but it is harder to tame a harsh negative.

 

[Photo_Smith]

I'd be very grateful if you could, without putting yourself to too much trouble.

Cheers,

R.

Ok for your delectation:

Here is a graph from Kodak Research (Theory of Photographic Process C.E Mees) showing zero agitation and up to 4 brush strokes per second (close to continuous)

Their* findings were that a small frequency of agitation will build density rapidly and much more than no agitation at all.
Also variations in agitation are less noticeable with a maximum difference of about 2x density between zero and continuous with a spead of 30-100%; this remained consistent between different developers and films including D76.

*C. E Ives and E.W Jensen Soc. Mot. Pict. Eng. (40, 1943)

 

[sevo]

this remained consistent between different developers and films including D76.

D-16 and D-76 are not all that different. It would be interesting to know whether it also happens with principally different (that is, non-physical) developers - it might be a matter of the sulfite action being less affected by depletion or saturation than the developer action, in which case it will be limited to physical developers.

 

[rkm]

What film(s) are you having problems with?

Cheers,

R.

HP5+ 35mm and ID-11 in a Patterson tank.

 

[Photo_Smith]

D-16 and D-76 are not all that different. It would be interesting to know whether it also happens with principally different (that is, non-physical) developers - it might be a matter of the sulfite action being less affected by depletion or saturation than the developer action, in which case it will be limited to physical developers.

They mention they used a range of developers including an MQ citric acid (Agfa final) and Kodak D85 with several emulsions with a flow method of agitation.

It seems agitation follows the pattern of never passing 100% more density than if zero agitation.

They seem to suggest that local p.h and gelatin diffusion coupled with the inertia point of developers is more critical than agitation for achieving density over normal development times.

 

[zauhar]

I always think of agitation as the third aspect or third tool in the box. Expose for the shadows, develop for the mid tones and agitate for the highlights. It is just another way to influence the final image. For me less is more. Dilute developer and hardly any agitation and for others continuous with a jobo processor or suchlike does the trick. I like the detail and texture in high values and try to keep them. Contrast can always be added but it is harder to tame a harsh negative.

Reading this discussion I would have to think that continuous agitation with a Jobo unit would have to provide a very different look compared to inversions or twirling. So, does continuous agitation provide the darkest highlights (highest contrast) in your experience?

And how do you decide which path to take when developing a roll?

Randy

 

[John Bragg]

Is agitation frequency more relevant with lower concentrations of active developing agent ? Surely D-76 or ID-11 at 1:3 would cause more local exhaustion and "compensation" than neat stock ?

 

[John Bragg]

Reading this discussion I would have to think that continuous agitation with a Jobo unit would have to provide a very different look compared to inversions or twirling. So, does continuous agitation provide the darkest highlights (highest contrast) in your experience?

And how do you decide which path to take when developing a roll?

Randy

Hi Randy. I favor very little agitation, but yes. Continuous with a jobo would produce the densest highlights in the quickest time. I give all rolls the same development and boost contrast in printing or scanning where nescessary.

 

[Photo_Smith]

John they seem be saying that the spread between zero agitation and continuous is around 100% density with any given developer.

There is also mention that p.h is more critical on local highlights with a drop of 0.7 p.h at highest density (zero agitation) increasing agitation will give more density in these areas. The relationship between dilution and p.h of solutions is complex and more dilute developers change chemical concentrations by a relative amount, not necessarily ions in the solution or p.h.
Basically more dilution slows the inertia point mainly due to solvents not breaking down silver for the reduction agents to take effect.

 

[John Bragg]

John they seem be saying that the spread between zero agitation and continuous is around 100% density with any given developer.

There is also mention that p.h is more critical on local highlights with a drop of 0.7 p.h at highest density (zero agitation) increasing agitation will give more density in these areas. The relationship between dilution and p.h of solutions is complex and more dilute developers change chemical concentrations by a relative amount, not necessarily ions in the solution or p.h.
Basically more dilution slows the inertia point mainly due to solvents not breaking down silver for the reduction agents to take effect.

So what about development to completion then? would it all level out given enough time and produce a dense but uniform negative ? Was history unkind to Mortensen ?

 

[Photo_Smith]

Very few film developers are designed to develop to completion, that practice by and large stopped in the 1930's
You can see from the posted curves the effects of agitation vs none; with no agitation you will never achieve full negative density compared to a small amount of agitation.