Rotation speed for developing tubes
I develop my 8x10 negatives in home made ABS tubes. I don't use "full" volume of chemicals, but rather I roll my tubes by hand slowly and alternately in both directions to make sure that the negatives are always wet with chemical. Because the chemical doesn't always cover all of the negative, I can't let them stand, so constant agitation is what I have to do. I have read somewhere that if I roll the tube too quickly and always in one direction, I will get something called bromide drag? I think I understand that to be (in very simple terms) a mechanical displacement of part of the emulsion causing a change in emulsion eveness and density.
So, if this is correct, the question is :
If the rotation speed is very slow, say just fast enough to keep the chemical constantly fresh, but the direction of rotation does not change, might I still suffer drag? or, is the directional change absolutely necessary?
The reason for switching direction is to break up standing waves. Or whatever the term is.
You need to rotate the drum enough to keep the chemicals around the walls of the drum. You don't really have a puddle at the bottom but it's rotating along the outside of the drum. Centrifugial force I guess pushing the chemicals outward.
One of the benefits of using a water bath to hold the tubes during agitation is that the tube "bobs" ...this contributes to a changing flow pattern. Another benefit is that the water bath contributes to a more stable temperature.
I found a tub that will hold my 8X10 tubes at Lowes...it was relatively inexpensive. I see that you are in Canada and probably don't have a Lowes...any building supply or discount store should have a plastic container of adequate size to do the job.
Nick and Donald,
Thank you for the replies. They are going to help a lot! The reason I asked the question was that I am getting even lazier than normal and I have been pondering building a motorised tube roller.
"Standing waves" and "bobbing end to end" are the keys to this project I think, so if I whip up a slow (say 10-15rpm) turning roller which also raises and lowers one end of the tube, then having waves travelling in three directions should eliminate standing waves even if it's only rolling in one direction.
cheers and thanks again
In my tests with the setup shown, I found even development without side-to-side agitation. I cut open-ended film tubes from 1.5 inch ABS, 15.5 cm long. I chose that length so that the 4 inch dimension of the film, when centered in the tube, appeared to be sufficiently far from the turbulence at the end of the tube (which would cause increased development), so that the entire sheet gets something closer to laminar flow. I cut a 4 inch PVC pipe section to 20.5 cm long and glued end caps with centered 5.6 cm diameter holes over both ends, large enough to easily insert a 1.5 inch pipe and extract it easily in the dark. These are not true 4 inch end caps that fit over the outside of the 4 inch pipe, but might be called test caps or something similar, and fit inside the pipe. Be sure to glue the end faces of the 4 inch PVC to the end cap securely, not just the interior of the pipe. The 4 inch pipe interior has small facets and won't seal completely. I run this setup on a Unicolor roller base, and can use reversing or single direction rotation. My setup takes something like 150 ml to cover the film, and the small tube rolls inside the large tube.
I also cut some 18 cm lengths of 2 inch ABS pipe and put similar end caps (with no holes cut) on one end of those. I can float one of the 1.5 inch ABS tubes inside a 2 inch tube and have 250 ml cover a 4x5 sheet. It floats and bobs, and the 1.5 inch pipe floats higher than the top edge of the 2 inch pipe, so you can just tap and spin the 1.5 inch film tube to agitate. I do this with the film near the bottom of the small tube so that it's completely submerged. I'm just starting to test this with semi-stand agitation, but see no reason that it shouldn't work.
Hope this helps. My main point is that I think you can get even development without having the tube tilt end-to-end. You might try it before making something more complex.
Last edited by Lee L; 05-13-2008 at 11:37 AM. Click to view previous post history.
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If you have a lot of tubes to do at the same time you should consider developing in a water bath. Phil Davis tested rate of rotation speed and found that it did indeed matter, but only at the extremes. Just rolls the tubes in the water gently and you will get good, even development.
Originally Posted by John Bartley
One direction rotation in a tube or drum on a motor base should be ok, especially if you get up and down lift. For very fine testing of film I place 4X5 or 5X7 film in tubes, with caps, and then place this in an 8X10 drum which I use on a motor base. The key to good develpment is to place the tubes holding the film in the drum on a diagonal so that you get up and down motion on a vertical axis along with the rotation on the horizontal axis.
Last edited by sanking; 03-27-2006 at 07:22 PM. Click to view previous post history.
Lee and Sandy,
Good information - thanks guys. The lack of need to incorporate rotation reversal makes this much simpler. Making the tubes (which are daylight tubes BTW) move in two planes is quite easy if the rotation is done with a rubber faced eccentric drive wheel.
John, just looked at this thread and I can add that rapid rotation can cause two problms.
First, it will increase the rate of development. If you were to try a time posted by someone else with tube development and didn't replicate their rpm's, it would yield different results. My first attempts at tube development were too rapid, so times were too short. This was due to using PMK for two years and, letting the film sit for too long would aways cause uneven staining. The suggestion about a water bath is a good one. I use a large tray or a rubbermaid tub is fine. Really helps control temperatures as well here in the desert.
Second, with too rapid a rotation you can end up with uneven development. This will show up as streaking which goes across the axis of rotation of the film in the tube.
I would encourage you to try stand development or minimal agitation at some point with Sandy's pyrocat. It is the easiest way to get consistently good results with full shadow detail and crisp edges. It also is a nice way to be lazy about development. Best, tim
Originally Posted by noseoil
I've found that using D23, I really have to have high temperatures to cause any troubles with time or grain. Fortunately around here, the average temp in our house is 18'c to 24'C except in very hot weather, so temps aren't an issue (not yet anyway - maybe I'm just not fussy enough )
I did three negatives yesterday and timed my rolling speed. I am rolling a tube once every 6 seconds, so about 10rpm. I think I'm going to go ahead and try single direction rolling at the same slow speed that I'm currently using. I like the ease and lifespan of D23 so much and it is so forgiving with regard to temperature that I'm loath to go away from it.