Vacuum Storage

[focus_on_infinity]

I was wondering if anyone is doing vacuum storage of their mixed photo chemistry, and if they've seen any appreciable benefit to it. I was experimenting with a 500ml bottle and a vacu vin stopper. I was able to consistently extract .2g of air from it using a hand pump, but no better. Air at 1 atm is 1.2g/l, so that's about a 33% vacuum. Not bad. Better than nothing. But not fantastic, either.

There are probably a couple of ways to improve the process. One would be to use a machine vacuum pump. I could probably do better with the accessory port on a vacuum sealer, but I don't see an accessory that fits on the vacu-vin stoppers. I don't really want to use the vacuum sealer that I use for food, and I'd like to keep this as cheap as possible. I have a 2.5CFM vacuum pump that I could probably just leave in the dark room most of the time, but I'd still have to figure out how to hook it up.

IIRC, the R134a connector is a 1/4" acme thread. I could probably find an adapter with a barb connector for a hose, but then I sitll have the issue about how to get a nozzle that fits on the vacu-vin. I suppose I could just use Foodsaver stoppers instead, but I already have the vacu-vin's.

Does anyone else do anything like this? I don't like the idea of using marbles, because it makes it harder to dump chemicals around with impunity. I do everything in 500ml sizes, so I like to be able to just dump my developer or fixer or whatever quickly into the Paterson tank. I don't want to go fishing marbles around. And I really don't want to do the wine bag thing, either, because I think using a vacuum sealed bottle sounds like a superior solution anyway.

So, for those of you who vacuum seal your chemicals, how do you do it?

 

[revdoc]

A different way to look at this problem: even a 100% vacuum will quickly fill with water vapour from the solution below, so why not just displace the air with water vapour?

 

[jvo]

i use glass bottle and tetanal protectan (argon gas, i think) to displace the air and sit on top of the chemical.
i prefer to call it 'glass marbles 2.0' to show how au courant i am!!

 

[focus_on_infinity]

i use glass bottle and tetanal protectan (argon gas, i think) to displace the air and sit on top of the chemical.
i prefer to call it 'glass marbles 2.0' to show how au courant i am!!

Yeah, I have a can of that stuff. It just seems wasteful to me, given what my processing habits may turn out to be. The vacuum seems very adaptable if I can get a strong enough vacuum to make it worthwhile.

 

[MattKing]

You don't get any benefit from reducing the pressure in the container.
You get benefit from reducing the contact between the solution and air.
Whether you achieve that by reducing the amount of air in the bottle, or inserting something between the air and the solution, it doesn't matter.

 

[focus_on_infinity]

You don't get any benefit from reducing the pressure in the container.
You get benefit from reducing the contact between the solution and air.
Whether you achieve that by reducing the amount of air in the bottle, or inserting something between the air and the solution, it doesn't matter.

How would that be? It works for wine, based on the same principles that affect photographic chemicals. It's something that consumes the O2. Reducing the pressure reduces the rate of consumption.

 

[MattKing]

It probably works for wine because:
1) it improves how well the cork seals the bottle; and
2) with wine the products of oxidation impede further oxidation once those products reach sufficient concentration in the air above the wine.
With photographic chemicals, it doesn't always work the same way.
Any reduction of available O2 probably helps, but I'm not sure that there is much reduction, unless the volume decreases.

 

[focus_on_infinity]

It probably works for wine because:
1) it improves how well the cork seals the bottle; and
2) with wine the products of oxidation impede further oxidation once those products reach sufficient concentration in the air above the wine.
With photographic chemicals, it doesn't always work the same way.
Any reduction of available O2 probably helps, but I'm not sure that there is much reduction, unless the volume decreases.

Could be. I played around with some bottles this evening, and looks like 50% is about as good as this stopper and and hand pump can get. I don't think any additional investment in this makes much sense, given the quantities of developer I can have around in full bottles. If it gives me a little extra life out of a smaller bottle, it's probably worth using the solution I've got.

 

[bnxvs]

As far as I understand, the main problem is oxygen dissolved in water. Even if you create a vacuum above the surface of the solution, this will not save from oxidation of the developing substances and damage to the solution. Or am I not quite right?

 

[focus_on_infinity]

As far as I understand, the main problem is oxygen dissolved in water. Even if you create a vacuum above the surface of the solution, this will not save from oxidation of the developing substances and damage to the solution. Or am I not quite right?

There are a couple of things to unpack here, I'll try to be methodical in the few minutes I have to reply.

First - if it were solely a question of already dissolved oxygen, then there would be no benefit to storing chemicals in filled bottles, regardless. There's definitely a question of how much gaseous oxygen is exposed at the surface.

Second - decreasing the pressure in the bottle decreases the amount of dissolved gasses in the liquid. A demonstration of this is to use a vacuum pump on a bottle of carbonated water. The dissolved CO2 will quickly exit the solution for the space above. This is perhaps one area where vacuum storage could be beneficial compared to filled bottles.

Third - decreasing the pressure, but not the point of a perfect vacuum is still beneficial, because it decreases the oxygen exposed at the surface, and thus decreases the rate that it will chemically react with surface material

That said, I'm not really going to do some heavy science on this one. I'm just settling into maintaining the chemistry, but I've kind of come to a system* where I'll have exactly one small bottle of a given developer that won't be filled to the brim, and I'm just trying to promote the shelf life of it a little bit, as much as I can, using the most convenient and non-wasteful method that I can come up with.




*Specifally, I'm thinking that for a developer, I'll have 3 categories of full-strength storage. 1.) long term, 2.) working/replenished full strength, and 3.) replenisher/one-shot. 1.) and 2.) will be filled to the brim. Only 3.) will be lower, because I'll be taking from that bottle to either a.) replenish bottle #2, or b.) mix a dilute one-shot.

 

[pentaxuser]

There are a couple of things to unpack here, I'll try to be methodical in the few minutes I have to reply..

Sounds vaguely ominous. I hope the lights are not about to dim in the cells a couple of times

pentaxuser

 

[focus_on_infinity]

Sounds vaguely ominous. I hope the lights are not about to dim in the cells a couple of times

pentaxuser

Well, if you hear an explosion, you'll have to decide for yourself whether you want to make a run for it.

 

[esearing]

filled smaller bottles

 

[tezzasmall]

i use glass bottle and tetanal protectan (argon gas, i think) to displace the air and sit on top of the chemical.

+1 for Protectan.

Terry S

 

[mitorn]

i use glass bottle and tetanal protectan (argon gas, i think) to displace the air and sit on top of the chemical.
i prefer to call it 'glass marbles 2.0' to show how au courant i am!!

It is a mixture of propane butane and isobutane (according to the german safty data sheet), so highly flammable and defenitely not argon
Difference to marbles is that overtime it will mix with the remaining air in the bottle (not sure how long it takes might be tens of years), if the container is only partly filled.

 

[revdoc]

As far as I understand, the main problem is oxygen dissolved in water. Even if you create a vacuum above the surface of the solution, this will not save from oxidation of the developing substances and damage to the solution. Or am I not quite right?

I used to think that, too. Then I found that dissolved oxygen in H2O is less than 6mg per litre at 20C, which isn't going to oxidise much.