Gas Burst Chemistry Oxidation Questions

[Tin Can]

Thiosulfates are more stable in air than say developing agents, but they do oxidize. This is one reason why even neutral (eg TF-5) and alkaline fixers contain sulfite to scavenge oxygen. In general, plain air is not the best idea for gas burst agitation in a B&W process. If you want maximum longevity out of your TF-5 with a re-use regimen, nitrogen would be the way to go. Alternatively if you stick with air, test your fixer at regular intervals. Using air will accelerate oxidation, but how much faster, we don't know. It may or may not make a meaningful difference in how long you normally run a batch of TF-5. All you can do is monitor it.

Hope this helps.

Yes, that helps.

Thank you!

[Harold_4074]

Michael R has it right; the thiosulfate will react with oxygen, at a rate partly determined by the rest of the formulation. The sulfite, as an oxygen scavenger, will convert to sulfate. It also stabilizes the thiosulfate against acidity, which is why pure thiosulfate solution will precipitate sulfur on contact with the carbon dioxide in the air. Presumably, there is more going on in TF-5 than these simple reactions; I don't know the formula and in fact still use TF-4, which has a recommended storage life and tray life which are probably based on oxygen permeation of the bottle and solution respectively.

Gas burst agitation creates a lot of air/liquid surface area, and the turbulence will pretty much eliminate concentration gradients, so whatever can happen to fixer in contact with air will happen a lot faster in a burst system than in tanks or even trays.

My worry would be that the degradation would not be gradual enough to trigger the "double the initial clearing time" test until suddenly a batch of film comes out stained, grainy, or otherwise compromised. Exhaustion of things like stabilizers, plasticizers and inhibitors can behave that way.

[Tin Can]

Michael R has it right; the thiosulfate will react with oxygen, at a rate partly determined by the rest of the formulation. The sulfite, as an oxygen scavenger, will convert to sulfate. It also stabilizes the thiosulfate against acidity, which is why pure thiosulfate solution will precipitate sulfur on contact with the carbon dioxide in the air. Presumably, there is more going on in TF-5 than these simple reactions; I don't know the formula and in fact still use TF-4, which has a recommended storage life and tray life which are probably based on oxygen permeation of the bottle and solution respectively.

Gas burst agitation creates a lot of air/liquid surface area, and the turbulence will pretty much eliminate concentration gradients, so whatever can happen to fixer in contact with air will happen a lot faster in a burst system than in tanks or even trays.

My worry would be that the degradation would not be gradual enough to trigger the "double the initial clearing time" test until suddenly a batch of film comes out stained, grainy, or otherwise compromised. Exhaustion of things like stabilizers, plasticizers and inhibitors can behave that way.

Thanks Harold,

I will be getting N2 in 2 weeks and will start using it on TF5 right away. Heretofore I was counting sheets and replacing fixer at a set schedule. I am now certain TF5 or any fixer will degrade faster with Air Gas Burst.

Then I will need to consider how to test in a discernible way the efficacy of N2 and Air on one shot Rodinal. That may be a poor quest.

If N2 cost over time is low enough, I will simply use N2 for all processes. The air compressor simply got me running sooner.

[Mark Sampson]

I won't contradict the chemists, but in the lab where I worked at Kodak we used nitrogen for the developer and air for stop bath and fixer. We (naturally) followed the recommendations engineered (and published) by our colleagues at Kodak Research Labs across the river. I never saw fixer degrade faster than normal- at least it always lasted until the 'square-inches of film' limit, when we replaced the stop bath and fix. All EK products of course...
As I recall, (this was c.1985), gas-burst systems were meant for full-strength, replenished developers and lots of film; not diluted, one-shot methods. But this may make no difference in practice.

[Jim Noel]

"As I recall, (this was c.1985), gas-burst systems were meant for full-strength, replenished developers and lots of film; not diluted, one-shot methods."
Correct. At the college we used N burst with D-23 on a replenishment basis, and air for the fixer. The D-23 was used for a full semester at which time I recovered it for use in total development when maximum increase in overall density and contrast was needed. Since the average usage was on the order of 1200-1500 sheets of 4x5 per month, the D-23 lasted well, but the fixer had to be changed sometimes every other day.
In the final years of using the system, we did not use gas burst for fixing, but had students remove film from hangers and fix in trays. This eliminated problems with under-fixed negatives.

[Harold_4074]

I never saw fixer degrade faster than normal- at least it always lasted until the 'square-inches of film' limit

That sounds entirely reasonable, since there is probably a good margin of safety built into the limit. My guess is that you were using either Kodak Fixer or Kodak Rapid Fixer (or the bulk equivalents--wasn't there something like Ektafix sold in boxed bags?) which was rather different from the TF series of fixers. Anything with sodium thiosulfate to which sulfuric acid is going to be added is probably going to need a lot more sulfite than a "neutral" fixer, which could play into the oxidation characteristics.

This thread has me wondering if the old formulas for fixer test solution are usable with the TF series, and if not, is there a formula that is? My suspicion is that the modern vendors of photographic chemicals, with the possible exception of Ilford, do not do quite as much research and quality control as the old Kodak did, and the published capacities may be extremely conservative. I think that the shelf life of TF4 concentrate is given as something like six months, which seems awfully short, and I know from experience that three-year-old bottles clear film in under sixty seconds, just like new stuff does.

[Michael Kadillak]

If there is one thing I learned in this LF/ULF photographic pursuit of mine is that gas burst is a time tested art form that does not need to be reinvented. Use N2 for development and adhere to what took Kodak decades to perfect - period! When I wrote the Gas Burst Article in View Camera years ago it was after a full two years of attempting to follow Gordon Hutchings Book of Pyro conclusions that were flat out WRONG. I did NOT need special tanks and hangers much to my dismay in believing that Gordon had done his homework which he simply did not. When I gained access to the Kodak Gas Burst article which I have shared freely on this forum the sky opened up. I am up to the largest N2 tank that one can purchase without going into the lease program.

[Tin Can]

Michael, I am not trying to reinvent anything and have not read Gordon Hutchings Book of Pyro.

Once I found the Kodak data I immediately moved in that direction. My Gas Burst set points are identical, but my developer is not. I may go to a replenishment developer system in the future.

I will be using N2 exclusively asap, 2 weeks.

I am curious about your developer. Are you using the same batch for long periods or mixing fresh often? Will you share what you currently do?

Your View Camera Magazine post was key in sending me down this path. There is very little data available. So I am searching for all I can find.

Thank you.

[Duolab123]

I have my copy of Kodak pamphlet E-57, revision 9-70. Says what all of you good folks are saying nitrogen for developer air for the rest. I actually have a BS in Chemistry, not that that makes me any kind of expert. The thing that occurs to me is that if you are using a one shot developer I would think you could very easily get by with air. If Rodinal survives use in Jobo drums with reels, roll or sheet film reels it should survive air bubbles for one cycle.
Also Kodak recommended for B&W 1 sec bursts, 6 times a minute. With Ektachrome in E-3 they say 2 seconds only once per minute.

Having said this our atmosphere is loaded with Oxygen. It amazes me how little air left in a partially full bottle of developer will spoil it. I don't keep partial bottles of stock solutions any more I have a bunch of PET bottles 2,4,8,16,32 oz and fill them to the very top. I have kept XTOL stock for over a year and never had a problem. I just dump the bottle into a beaker then fill the bottle with DI water to make 1:1 Xtol, have used this method for at least 15 years.

[Harold_4074]

I have my copy of Kodak pamphlet E-57, revision 9-70. Says what all of you good folks are saying nitrogen for developer air for the rest.

I'm pretty sure that TF5 was not the fixer of choice in 1970; the chemistry of thiosulfates hasn't changed, but the formulation of fixers has. I wouldn't say that air is bad for agitating fixer, but unless you are talking about an acid, hardening fixer based on sodium thiosulfate, I wouldn't say that it is necessarily innocuous.

Also, there is theoretically a big difference between bubbling fully oxygenated air through developer and putting the same developer into a sealed container with a small amount of air for the same amount of time.

Some testing would be needed to settle the issue one way or the other, but life is short and nitrogen is cheap...