Tank development and automated agitation

[Draganski]

Hi
I have just boought some Kodak hangers for 4x5 film on ebay. My idea is NOT to use the dip and dunk method.

I would use a magnetic stirrer at the bottom of the tank to agitate the liquid, not the holders. I would probably develop 4-6 sheets at a time. After that lift the negatives and put them in the stop bath, fixing etc.

Is that a bad idea, does anyone have any experience with something similar?
If that doesn't work i will use the hangers for washing the negatives.

[pdh]

My immediate thought is that using a magnetic stirrer to move the developing solution might set up "standing waves" in the liquid and leave you with a pattern of uneven development.
All the technical texts on development I have read stress the need for agitation to make flow of the developing solution as random as possible

[Draganski]

I could switch off the stirrer intermittently. Or maye use an aquarium pump instead?

[vinny]

I think you'll get surge marks and uneven development.

[LabRat]

So what's so wrong about dipping and dunking a rack of hangers during the development??? Is it dark in there??? Too scary!!!!

As I understand, agitation is needed because as areas of higher density develop, a "cloud" of developing by-products that form around those areas (that both accelerate and restrain local development)... Something is needed to break up these clouds, because they will "leak" or break up unevenly due to turbulence, gravity, etc causing the dreaded "bromide drag" streaking of higher and lower density...

The surface of film develops a "boundary layer" where the increase of flow over this layer increases this layer... (Sort of like the wind over a wing of an airplane... The wind doesn't hit it directly, it flows around it...) This prevents these "clouds" from breaking up fully and evenly...

If you agitate it too fast, it agitates less...

Or develop turbulence that has different flow patterns, or with a magnetic mixer, maybe even a vortex flow pattern!!!!

By raising the film out of solution during it's steps, it breaks the "boundary layer" as the drainage from the surface thins this layer to a minimum... But it needs enough agitation cycles so the "clouds" are evenly dispersed away...

Steve K

[Draganski]

i just like constantly very good results. it is easier to reproduce something exactly with a machine than by (my) hands.
Besides, I like figuring out new solutions.
I have read that a lot of the developing process is about diffusion of molecules from this gelatinous layer, a concept i am familiar with as a pharmacist. sometimes the journey is the reward.

[pdh]

In any method of agitation it is imperative not to get streamlined flow over the emulsion surface. The flow of the developer over the emulsion surface must be as random as possible, otherwise one or more of the various forms of 'streaming' may result

(Mason was head of research at Ilford for many years)

[Tin Can]

Look up Gaseous Burst.

I am setting up a system. Fairly simple.

Search DIY.

[Light Guru]

Why not just do stand development?

[Peter De Smidt]

Randy's right. For what you want, nitrogen burst is the way to go. A magnetic stirrer will cause more agitation on the bottom of the tank than on top, which will lead to uneven development. Stand development can work, but it can be a tricky method to get even development with.

[tuco]

I use a machine I made to agitate my 4x5 sheet using a daylight HP Combi-Plan tank (now discontinued I think). I process it just like my 120 roll film. Works like a champ. A good agitation method/profile avoids laminar flow across the boundary layer of the film thereby maintaining fresh developer to react with the film on each agitation cycle.

[Michael Kadillak]

Gas burst can be modified to do stand and semi stand development. I wrote an article in View Camera a while back and have forwarded the Kodak publication on this subject regularly. Read the article since there is no need to go to the elaborate and unnecessary recommendations in the Book of Pyro by Gordon Hutchings. Been there and done that. Kodak 4a hangers work marvelously as long as you have 15# at the delivery side of your plenum and get a 5/8" rise in your tank.