Bottle caps and liners - are some preferable to others?

[Steve Goldstein]

I use glass bottles, both amber and clear, for liquid photochemical storage. The caps themselves are a hard plastic (phenolic?), some black and some green. There are (at least) two types of cap liners available - metal foil on fiber/cardboard and PTFE. I think vinyl liners may also be available.

Over the years I've learned the hard way that metal liners are eventually attacked by working-strength stop bath, so they're clearly a poor choice for acids and I use PTFE there. That's the easy part.

How about for basic solutions like developers and some fixers? Is there any practical difference between the black and green cap bodies? Would I be better off with metal foil or PTFE in terms of forming an oxygen barrier? Would adding layers of plastic kitchen wrap between cap and bottle add any value in terms of extending solution life?

I'm curious because sometimes it can be months between my b&w printing sessions and I don't want to needlessly waste chems. [Some might say that my prints are a waste of chemicals, that's a separate issue...]

Gerald? Ron?

 

[Gerald C Koch]

The best overall cap has a conical liner to help it seat into the bottle neck. This type cap can be washed thoroughly and used over and over again. A flat plastic liner would be the second choice. A cap with a cardboard liner should only be used once as it may absorb some of the solution. A metal foil lined cap should never be used.

If the green caps are made of hard plastic then there should be little difference between them and the conventional black bakelite caps. Adding plastic wrap will not extend the life of developers.

Another possibility are black rubber stoppers like the ones used in labs. These can be washed and used repeatedly. They do eventually become hard with age and will no longer seal properly. But they are cheap and can be used for several years.

 

[fotch]

I was told by a chemist that Saran wrap does work as needed and that the generic plastic wrap does not work. ????

 

[AgX]

If you worry about the diffusion through caps, you might consider:

-) wrapping the cap with aluminium foil and sealing it with tape

-) inserting a stainless steel disk between liner and cap where appropriate

 

[flatulent1]

The darkroom instructor I studied under a few years ago used to put a bit of Saran Wrap over the mouth of the bottle before she put the lid on. She was using a plain PET bottle for XTOL, and had been doing this for years. She didn't do this with the other chemicals that I ever saw. I use glass bottles that have caps with partial cones formed in them. I would never use kitchen foil.

 

[Gerald C Koch]

If it makes you fell better to put a piece of plastic film under the cap then do so. It will keep the liner from becoming contaminated. But it will have very little effect on the storage life of the solution.