You can always put a piece of Saran wrap under the cap before screwing it
down.  "Original" Saran wrap is made of a different plastic, vinylidene
chloride polymer, than most food wraps, polyethylene,  so accept no
substitutes.

On 11/6/2004 7:25 PM jjs spake thus:

Good point, that. But it shows that I'm an amateur who uses chemistry rarely
enough that it *is* an issue in my case, possibly like others here.

It can still be an issue, suppose your processing a special film, and
the only developer you can get for that film comes in a 25 litre size.
You need to mix this 1 part concentrate with 3 parts water to make a 1
shot solution.  Your tank needs 500ml, so out of your 25L bottle you
need 1/8L (125ml).  At 1 roll per day, you will take 100 days to go
through that 25L bottle.  The concentrate, when exposed to air lasts a
week.

One thing is that we are not the only ones with this problem, wine
makers have  been dealing with the problem of keeping oxygen out of
their red wines over an extended period of time, for centuries.

They may offer us the best solution, pick up some dark 1L wine bottles,
corks, and those fancy plastic cap covers at a wine making store you may
need to purchase a corker and sealer to do it properly.  Pour the
solution into the bottle until full enough, add a cork and seal.  Use
different seals for different chemistries.  When you need a new bottle
of chemistry, pull off the seal and remove the cork.  Now write the date
on the label, and whatever isn't used in time, you toss.  However you
keep the bottle and maybe the cork for reuse (if you can't reuse the
cork, then they are usually cheap).   Maybe you used only a little of
it, maybe you used most of the bottle.   Beats losing all of it.

I have not tried this, but will as soon as I get my darkroom running again.

W

On 11/8/2004 2:50 PM Dan Quinn spake thus:

I know it came up, but there was no data, which was what I was after in my query.

Good thing someone else here actually posted something useful. Following James
Robinson's tiny URL, I retrieved the following table that was posted here back
in July:

Note that PET (aka PETE) seems to be much, much better than polycarbonate. (At
least so far as permeability is concerned.)