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  #21  
Old 13th May 2020, 05:52 PM
Tony Marlow Tony Marlow is offline
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Just as a matter of interest regarding argon and protectan, the density of air in normal conditions is 1.205 KG/cubic metre, argon 1.661, Butane 2.489 and propane 1.882. Would butane (? Protectan) be more efficient at keeping oxygen away than the lighter argon?

Tony
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  #22  
Old 13th May 2020, 09:27 PM
John King John King is offline
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Bob, what I have found is when you do manage to unscrew the cap the seal remains in place on the bottle top and you have to lift it away with a fingernail to let the air in, the seal is that good..

I have made a tool out of 2mm alloy strip that fits snugly round the side of the cap to release it - no more struggling with makeshift items.
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  #23  
Old 14th May 2020, 07:56 PM
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Martin Aislabie Martin Aislabie is offline
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Quote:
Originally Posted by Tony Marlow View Post
Just as a matter of interest regarding argon and protectan, the density of air in normal conditions is 1.205 KG/cubic metre, argon 1.661, Butane 2.489 and propane 1.882. Would butane (? Protectan) be more efficient at keeping oxygen away than the lighter argon?

Tony
Hi Tony

All 3 gases are heavier than air - so sink to the bottom of the bottle (or onto the surface of the liquid) - so it doesn't make a fat lot of difference.

Martin
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  #24  
Old 14th May 2020, 08:46 PM
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Quote:
Originally Posted by Tony Marlow View Post
Just as a matter of interest regarding argon and protectan, the density of air in normal conditions is 1.205 KG/cubic metre, argon 1.661, Butane 2.489 and propane 1.882. Would butane (? Protectan) be more efficient at keeping oxygen away than the lighter argon?

Tony
I guess in theory a heavier gas would be less prone to expose the liquid to air by physical movement or temperature fluctuations causing convection currents in the gas. I don't know if the differences are likely to be enough to cause a problem but we tend not to shake or expose developer to sudden and significant temperature differences anyway... If we assume the gas takes up 90% of the space above the liquid, then quite a lot of perturbation would be needed to expose the surface of the liquid to the air. I imagine the gas/air boundary to look something like the water/air boundary (but with deeper waves given the much lesser differences in density).

Or, the shorter version: I don't know but I suspect it is not a problem in practice.

Last edited by Bob; 14th May 2020 at 08:50 PM.
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  #25  
Old 17th May 2020, 12:59 PM
SpencerB SpencerB is offline
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Oh wow thank you so much for all the advice! I decided it was a bit foolish to use the old plastic bottles. But I found a set of 3x 1 litre black plastic bottles (https://www.ebay.co.uk/itm/3X-Darkro...72.m2749.l2649) which I squeezed the air out of when I mixed the batches up. I actually like very much the idea of amber glass and I think next time I will get this. I have heard that it is a good idea to use glass marbles to keep the air out?

Also I saw the comment on the use of a microwave to create a vacuum seal! Amazing! I used to can food with a pressure cooker when I had a lack of freezer space. Could I do that with these bottles? Or would they break? also my microwave isn't big, I wonder if I could put them in hot water on the hob? Sounds a little risky though
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  #26  
Old 19th May 2020, 12:53 AM
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One snag with marbles is that you need a quite surprising number of them to make up for more than a few tens of ml. When discussed before, I don't think anyone who has tried them (like me...) has stuck with them - but I may be wrong about that.

The microwave is just to heat the chemicals a little - the small partial vacuum created when the liquid cools is just to ensure a good seal rather than to remove the air. You could do the same by putting the filled bottles in hot water already heated to say, 45 C, for a while before sealing them - the microwave is just quicker and less faff (but be careful not to overheat the developer). I don't do that atm, but I thought it was a good idea from John as the pop when you break the seal will tell you the seal has not leaked since you screwed the top on.

I would keep an eye on those bottles to make sure they remain squeezed-in. If you have b&w chemicals in them, the only one you need worry about is the developer. I don't do colour so I'm not sure if any of the other colour chems need care to keep the O2 out.

Last edited by Bob; 19th May 2020 at 01:05 AM.
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