KRST bottle - vacuum?

[clayne]

Strange thing I noticed today - I have a bottle of nearly full KRST (1+3) that I keep around for negative toning (contrast control) and the bottle was doing one of those sucking itself in type of things. The darkroom has maybe had a variance of 10 deg F over the past month or so and humidity is relatively controlled around 60%. Anyone ever seen this before? I opened the cap and of course could hear the sucking in of new air and just re-tightened and put it back up on the shelf afterward.

It doesn't bother me too much, but was just curious if anyone else has seen a similar effect.

 

[Anon Ymous]

Yes, it also happens at higher dilutions and I suppose it is a sign of oxidation. One or more chemicals in the bottle probably reacts with oxygen, but since the bottle is well sealed, it has to reduce its volume. I've also noticed it with developers, fixers, but not with stop bath. I assume there's nothing to oxidise in a stop bath bottle.