Well how about the kind of developer? I mostly use Rodinal, pretty dilute stuff. You use a pyro developer? Might be if I used your developer I'd start having that problem too and have to adapt. There has to be some real reason for it.
Makes me real curious.
Lately I've started using dip n dunk for my C41, I was getting a bit leery of the fill times for the tall tank as compared to the 3:15 developing time. Didn't leave much leeway. Besides that the damn lid always leaked and I hated how the bleach would dribble everywhere while I inverted the tank. Dropping the reels into prefilled tanks is so much cleaner!
""The difluoroethane in products like "Dust Off", typically used to move dust off film and into the air, is unreactive and will displace air quite nicely.""
I had thought of doing this but hydroflorocarbons never seemed like they qualified as inert. I would try it by I am not a chemist and am concerned about reactions in chemistry I don't completely understand: C41 for example. None of my B&W chems really need this - I do use marbles - dark glass and mix only what will be used in a short time.
As far as presoaking goes - I can't imagine not presoaking 4x5. I think 35mm would probably not care. My first 4x5 tank was square. I wasted a whole box of film learning that square daylight tanks are the wrong answer - I always got uneven development. Even with the Jobo tank, I always presoak off the anti halation layer. I read (Adams) that it takes 20 seconds for the chems to permeate the emulsion. It makes sense to let the chems displace the water evenly as opposed to permeating the emusion at different rates in different spots. I also don't want that unknown chemical disolved layer in my developer. Of course C41 was designed to run that way.
</span><table border='0' align='center' width='95%' cellpadding='3' cellspacing='1'><tr><td>QUOTE (glbeas @ Apr 12 2003, 07:16 PM)</td></tr><tr><td id='QUOTE'>
I was getting a bit leery of the fill times for the tall tank as compared to the 3:15 developing time. Didn't leave much leeway. </td></tr></table><span class='postcolor'>
I guess I'll have to take my place with the "odd" crowd again.
I've made my share of mistakes when it comes to processing ... wrong temperature, wrong time ... needless to say, a *host* of others. I've come to view these "excursions" as "interesting experiments" in alternative processing rather than "disasters."
I would submit - prepare for sacrilege - that color processing .. both C-41 and RA-4 is nowhere near as sensitive as the film producers would have us believe. My theory is that, if the results out of the darkroom are not up to the expectations of the "small operator" - imagined or real - the manufacturers can always fall back to, "Well, you didn't maintain a developer tolerance of +/- 1/4 degree F!!" Saves them a lot of time in technical service calls.
JOBO did a *lot* of investigation into the "uneven development" idea - the operation of filling their tanks allows the developer to reach the outer film on the reel before that on the inner - and after knocking themselves out trying different film/developer/fill times with *many* densitometer readings, concluded that, for all intents and purposes - even among the "pickiest" - there wasn't diddly-dit of difference. I think the greatest variation was something on the order of 0.01, which could be caused by a LOT of other factors.
I remember reading - both from Ilford and Agfa - that pre-wetting was to be avoided - something to do with water "swelling" the emulsion and causing image degradation - without adding anything to "even-ness". For a time, the idea of adding a wetting agent - dilute Photo-Flo, or my choice for wetting, the Edwal stuff - to the developer was in vogue - but that sort of "faded".
I have been wondering about the "No less than a five minute devloping time" proscription for some time now. I've done a *bunch* of 3 minute and 15 seconds C-41 processing over the years with *no* "uneven development" problem that I could see.
As a matter of fact, Irving Penn in his book "Worlds in a Small Room" states that most of his photography was done on "Tri-X , exposed at 160 ASA, or 80 to 125 for very dark skins. Development was usually in (Ethol) UFG , 3 to 5 minutes at 68F." Note the "three".
Considering Penn's work in this book, I'd have no problem doing the same. If my work could only be half as good...
</span><table border='0' align='center' width='95%' cellpadding='3' cellspacing='1'><tr><td>QUOTE (Ed Sukach @ Apr 11 2003, 12:27 PM)</td></tr><tr><td id='QUOTE'>I contacted JOBO tech for information on a "Protectan" subtitiute - got a "You're on the List" answer ... so I'm waiting.
JOBO did reply ... I received this back on Sunday, the 13th ... Someone dedicated enough to reply on a Sunday?!!!
Subject: Protectan Spray
Date: Sun, 13 Apr 2003 12:38 EST
From: Mark Williams <email@example.com>
To: `Ed Sukach' <SukachEd@netscape.net>
Tetenal decided to stop shipping this to us, despite the fact that it sold well. I don't know why. The can was a mixture of propane and butane. I know of people who have stared using a plumber's torch (propane) to fill the bottles, and some who have used canned air from the enlarger area.
We have never tried or used argon gas, so I don't have any comment on that. You can check it out with the various online chat rooms dealing with photography and see if any one has used argon gas. For my money, the plumber's torch works fine. However, the company does not officially endoese this method (IE-some knucklehead will blow up their basement-even though Protectan is just as flammable).
(734) 677-6989 X9440
Check out PermaJet papres at www.PermaJetusa.com
I appreciate this a great deal, not only for the "Sunday" response, but for the fact that Mr. Williams had the ba -- uh ... testicu .... uh ... *SISU* to honestly say "I don't know", instead of piling on a bunch of beef by product.
I'm going to continue the search. I see, from the "Wine" sites that there are also "vacuum" devices used to withdraw air from opened bottles...
It could be that Tetenal was afraid of the "explosive knucklehead" and that was their reason for discontinuing Protectan.
"The can was a mixture of propane and butane. "
Holy shit! I always thought it was some inert gas. and I always made sure I used plenty of Protectan in my closed darkroom to make sure the chemicals didn't oxidize! When I get home I'm going to read the label on the can. and to think I was more concerned about using pyro... http://apug.org/forum/html/emoticons/smile.gif
It's been my experience that even working strength RA-4 tetenal lasts 2 months in a bottle without a problem.
Propane and butane are inert...to most reactions but combustion.
Add fluorines instead of hydrogens, as in the case of difluoroethane in "Dust Off", and the gas remains unreactive and is less combustable. Add lots of fluorines and chlorines, and it becomes completely inert and damages the ozone layer.
There is a problem with using any of these gaseous products: once you've displaced the air in the headspace of your container and seal it, the new gas, because you have not bubbled it through the solution, will begin to dissolve into the liquid and create a negative pressure in the bottle, possibly inspiring air. Any gas will do this if it is added in the gaseous form. Gasses in the (temporary) liquid state will too, but when they evaporate they create enough of a positive pressure that when some gas dissolves there is still a positive pressure in the container to keep additional oxygen out.
But speaking kinetically, refridgeration is more effective for preserving oxygen-sensitive solutions than replacing air with inert gasses, at least over periods of a week or two. That is, if the solution's solubility isn't harmed by cooling.
hmm, interesting. well, I can tell you that on a Wing Lynch machine, the nitrogen does two things. Primarily the pressure in the tanks works to pump the solutions out and into the processing trough located above. The tanks are sealed up, and a nitrogen blanket is laid down on top of the remaining chemsitry this way. It's really a simple processor in a way, and very trouble-free, because there's no pumps to worry about it--the only moving part is a drive bar--that rotates the tube sets you load your film onto. At any rate, even with a setup like this, using the best nitrogen grade, you get about 2-3 weeks tops for E6 chemistry. One thing they'll recommend, even while using the nitrogen blanket as a selling point--is to "top off" the chemistry weekly with fresh mix. So you pretty much try to turn it over ASAP. My experience has been that after a week, you can start to see things like the color dev starting to darken a bit, and maybe the first dev. turning slightly as well--the sorts of visual indicators of oxidation...we usually try to use it every day, and top it off at least once a week. btw--the way they recommend topping off, is to purge the nitrogen actually as you reseal the tanks--they have these rubber gaskets for a seal. You pump out a bit of chemistry and screw the cap on & seal it up. When the seal is made, the chem runs down the drain...the nitrogen runs into another part of the tank though, along with the heaters & temp probes etc. The whole beast sits there at processing temp round the clock, ready to go.....
The MSDS available from Jobo USA website has always disclosed the composition of Protectan as propane/butane.
The approach is to displace the oxygen in air with some inert gas. Propane and related compounds have the advantage of liquifying at room temperature under pressure -- this allows a larger quantity to fit within the can. The obvious disadvantage is the inflammable nature. Nitrogen, argon or other noble gasses should work well. You don't need a super high purity grade -- as long as you greatly reduce the amount of oxygen in the bottle, the lifetime of oxygen-sensitive photochemicals will be extended. Argon probably wasn't selected for the photo trade because of its expense. Propane/butane doesn't sound nice for wine and might impart a flavor, hence the selection of argon.
Another consideration is the container. Many plastics, even those used for some bottles intended for photochemicals, are permeable to oxygen. I have had the best results keeping B+W developers using glass bottles. The disadvantage of glass is the weight, breakability and possibility of injury from broken glass. Another approach is to limit the amount of oxygen by using full bottles -- either use smaller bottles, or add marbles. The smaller bottles will work if the material is impermeable to oxygen -- if the material is permeable to oxygen, the higher surface area to volume ratio of a small bottle will increase the oxygen reaching the photochemicals.