Agitation using magnetic stirrers

[cyrus]

So I was thinking of the article in View Camera about nitrogen burst agitation, and it occurred to me that a magnetic stirrer can be a cheap way of agitation too - for whatever it is worth. I think the speed of the stirrer can be adjusted minutely too.

[Vaughn]

Boy, I can imagine all sorts of problems using a magnetic stirrer. You'd have to play around with a lot of different tank configurations to over-come uneven agitation. For example, a deep tank with the film in racks -- one would most likely get more agtation on the bottom where the developer would be moving pretty good, but less towards the top where the film would be slowing the movement of the developer.

I have a funny feeling that no one uses a magnetic stirrer for a good reason...

Vaughn

[Greg Lockrey]

I would imagine that the eddy current patterns would be very defined and noticable on the developed negative. Less is more with negatives I have found.

[Michael Kadillak]

To get a sense of this for yourself, perform a simple test like they do in fluid mechanics lab at engineering schools. Set up your magnetic stirrer in a glass beaker and drop some ornamental "floaters" in the fluid from the hobby store and watch the flow patterns when the stirring speed is adjusted. You will observe the defficiencies in this technique fairly quickly for yourself.

The good news is that folks like you are thinking about options and alternatives and that is a very good thing.

Cheers!

[Donald Qualls]

Actually, if you could set up a magnetic stirring driver that would reverse every 10-15 seconds, you'd get a lot of small-scale eddies and very little larger-scale, stable flow patterns, and it would probably work very well. I presume this would be mostly applicable to a deep tank, which would require a largish stirrer in any case (or maybe multiples, which could be set to reverse at different intervals to keep the flow broken up even better). It might even be sufficient to just stir intermittently, which would be simpler to manage with most magnetic stirrers (reversing them would be like reversing an induction motor -- more complicated than just reversing the input wires, as I recall).

It'd be moderately expensive to set up, but MUCH cheaper to operate than nitrogen burst (though you'd still need oxygen infusion for the bleach in a C-41 line, that can be done with air from a compressor, no high pressure tanks needed).

[fhovie]

Agitation has to be somewhat random - I cannot imagine this making negs without marks made by the eddys.

[Scott Davis]

I do know that magnetic stirrers are useful in mixing chemistry, but I can imagine how problematic they would be for agitating a deep tank. Magnetic stirrers have to be running continuously in order to function. I would also imagine it could be possible to cause problems with image formation just like X-ray/CT-scan machinery does in the airport. Perhaps the magnetic field(s) required to operate such a stirrer would not be strong enough to affect a negative, but I don't know I'd want to chance it either.

[steve simmons]

With all of the established and successful ways of developing film - hangers and tanks, trays, the various rotary methods, gas burst - why you want to try and reinvent the wheel.

What would this method offer that the others don't?

steve simmons

[Ole Tjugen]

I do know that magnetic stirrers are useful in mixing chemistry, but I can imagine how problematic they would be for agitating a deep tank. Magnetic stirrers have to be running continuously in order to function. I would also imagine it could be possible to cause problems with image formation just like X-ray/CT-scan machinery does in the airport. Perhaps the magnetic field(s) required to operate such a stirrer would not be strong enough to affect a negative, but I don't know I'd want to chance it either.

I agree with the first sentence, but I can't even begin to imagine where you've got the rest from. :)

None of those are worth worrying about.

But: A magnetic stirrer is useful for mixing chemicals for precisely the reasons why they won't do a good job as agitators in a deep tank: They stir "systematically", from the bottom up. That means they will quickly even out differences in density, like lumps of solid chemicals in the bottom of a beaker.

Good agitation in a developer needs quite a lot of random action, which is precisely what magnetic stirrers don't give.

[Vaughn]

What would this method offer that the others don't?

steve simmons

Ah, but Steve, magnetic stirrers are just plain fun! After many years of mixing gallons upon gallons of Kodak fixer and Dektol by hand, obtaining a magnetic stirrer for the university darkroom was bliss! Without it, I would probably have a nasty case of Stirrer's elbow by now!

Even unworkable ideas have their value...personally I had never even considered the possibility before!

vaughn

[sanking]

Ah, but Steve, magnetic stirrers are just plain fun! After many years of mixing gallons upon gallons of Kodak fixer and Dektol by hand, obtaining a magnetic stirrer for the university darkroom was bliss! Without it, I would probably have a nasty case of Stirrer's elbow by now!

Even unworkable ideas have their value...personally I had never even considered the possibility before!

vaughn

If this could be made to work it would have the same appeal as nitrogen burst agitation, i.e. you could just start development and go away and let the magnetic stirrer do the agitation. The key would be to induce some kind of random pattern in the flow of the eddies. There are a number of potential problems but with some thought there is certainly a possiblity that it could be a practical system of development.

Sandy King

[steve simmons]

"If this could be made to work it would have the same appeal as nitrogen burst agitation, i.e. you could just start development and go away and let the magnetic stirrer do the agitation."

This is also true of some of the rotary pocessing equipment.

I am still trying to figure out what it is about either trays, hanger and tanks, rotary proessing, or gas burst that magnetic agitation is going to solve.

steve simmons

[cyrus]

"If this could be made to work it would have the same appeal as nitrogen burst agitation, i.e. you could just start development and go away and let the magnetic stirrer do the agitation."

This is also true of some of the rotary pocessing equipment.

I am still trying to figure out what it is about either trays, hanger and tanks, rotary proessing, or gas burst that magnetic agitation is going to solve.

steve simmons

I dunno. It was just a thougt -point is that there's a way to get the liquid to move using magnets as the basis of an agitation system. I am doing the "big picture" thinking, and let the details to be worked out by others. :)

[cyrus]

I do know that magnetic stirrers are useful in mixing chemistry, but I can imagine how problematic they would be for agitating a deep tank. Magnetic stirrers have to be running continuously in order to function. I would also imagine it could be possible to cause problems with image formation just like X-ray/CT-scan machinery does in the airport. Perhaps the magnetic field(s) required to operate such a stirrer would not be strong enough to affect a negative, but I don't know I'd want to chance it either.

Magnetic fields would not affect negs.

[Greg Lockrey]

Magnetic fields would not affect negs.

It's not the magnetic fields, it's due to the regular currents that these make while stirring.

[Donald Qualls]

I am still trying to figure out what it is about either trays, hanger and tanks, rotary proessing, or gas burst that magnetic agitation is going to solve.

Compared to nitrogen burst, you don't have to keep paying to get your nitrogen bottles refilled. This would really be applicable only in deep-tank systems where nitrogen burst is now used; magnetic stirring in trays would be very prone to scratching negatives, while rotary processing already has agitation built in. Any system where you can reduce an ongoing cost has an advantage, over time; magnetic stirring drivers aren't free, but they last decades with virtually no maintenance, while the magnets that go in the liquid are relatively cheap (and could be made easily and still more cheaply with epoxy resin and common bar magnets, so no need to pay lab equipment prices).

The trick is to avoid the systematic flow cells that continuous magnetic stirring will tend to set up, and the key to that is probably a combination of reversal, multiple stirrers, and intermittent stirring. Use of an agitator that isn't the classic "horse capsule" shape might help, too -- picture an agitator shaped like the aluminum base plate of the small flying fireworks that were commonly sold before "Safe and Sane" took over the world: a disk with fan blades pressed in. Make one of those from stainless steel, attach a bar magnet with chemically inert epoxy (fully enclosing the magnet) and you'd have a stirrer that generates a primarily upward-directed flow. Same thing with vertical blades instead of angled, and you get down-and-out flow. Alternate between driving, say, three of one and three of the other in the bottom of a 3-gallon tank, with rest periods between, and you'd have agitation that might begin to simulate nitrogen burst (or you might find out you're better with half a dozen of the upward sort).

The first fellow who tries this will spend some money and a fair amount of time in the dark getting it right. Then, however, he'll be able to sell it as an alternative to nitrogen burst that will make a line using the magnetic method cost less to operate than nitrogen burst -- and thus more profitable over some long term.

[Michael Kadillak]

Compared to nitrogen burst, you don't have to keep paying to get your nitrogen bottles refilled.

Paying $15 every other year (or longer) for 65 ft3 of nitrogen is really not a major expense in the larger scheme of things. I know folks that process fairly regularly with N2 burst and have used the same nitrogen tank for nearly three years.

But at the end of the day what is important are the results that any process accomplishes with your negatives relative to consistancy, ease of use, system maintenance costs and operational flexibility. Cost effectiveness needs to be considered, but this variable should be looked at over a reasonable period of use say 5 + years. All I know is that with a JOBO system I am concerned about replacing pumps, gears, tanks and other moving parts that will eventually wear out. With a gaseous burst system the only moving part is the solenoid valve and Ansco claims that they have been tested for years of use with no noticable degredation of effectiveness. That and the long standing history of producing negative to professional standards is what got my attention with this system and to study it further.

[sanking]

"If this could be made to work it would have the same appeal as nitrogen burst agitation, i.e. you could just start development and go away and let the magnetic stirrer do the agitation."

This is also true of some of the rotary pocessing equipment.

I am still trying to figure out what it is about either trays, hanger and tanks, rotary proessing, or gas burst that magnetic agitation is going to solve.

steve simmons

Compared to rotary processing the difference is that both nitrogen burst and magnetic stirrer systems offer the possibility of even development with very reduced agitation. Reduced agitation gives slightly greater effective film speed (desirable) and greater adjacency effects, which can increase apparent sharpness (also desirable).

There are a number of practical obstacles to overcome but I believe there is a lot of potential in a system based on magnetic stirrer, as there clearly is in nitrogen burst systems.

Sandy King

[steve simmons]

OK, I will wait and open my mind for future possibilities.

steve

[Vaughn]

If this could be made to work...

Sandy King

Lots of ideas are unworkable until someone comes along and figures a way to make it work. I guess that is why we have this magical thing called photography;) !

vaughn

[Jorge Gasteazoro]

There are many kinds of magnetic stirrers now, some in the shape of a cross, some in the shape of a triangle, etc, etc. If you can get one of these stirrers coated in a way such that "paddles" protude from them at different lenghts and places, you could probably get a more random agitation pattern than the typical funnel obtained when the stirrer is spinning.

[fhovie]

Or the best idea yet - stand processing
It is free
It is easy
It is relaxing
It compensates
It increases film speed
It is hands on, like - uhhhh - a hobby
GEEEZE - what an idea. .... of course .... I am an amateur.

and the Titanic was built by professionals, the Arc was built by an amateur.