In article ,
bkr wrote:

I have a couple of different cans of varnish that I opened and dispensed
into smaller containers for use. Now the varnish has hardened in all
the various conatiners, whether sealed or not. I know it has to do with
reaction to the air, but I don't know how to prevent it. I've seen a
couple threads that I think suggested adding some other chemical to the
can that wouldn't mix with the varnish but would displace the air.

As others have mentioned, it's the oxygen in contact with the varnish
that's causing it to cure in the can. You need to:

a) eliminate as much oxygen as possible by replacing it with an inert
gas like nitrogen, propane as others have suggested tho I've never
tried, or a commercial product like Bloxygen.

2) reduce the amount of oxygen containing air in the container by either
squeezing the sides of the container before capping, putting inert
marbles (glass fer instance) in the varnish to increase the material
volume, or pour into smaller container so that it's full before capping.

III) place a non-reactive material on the surface of the varnish to
isolate the oxygen from the varnish. This can be a layer of plastic wrap
or a few tablespoons of solvent like mineral spirits. If you go the
solvent route, gently spoon it on the surface and you don't want to
shake the can afterwards or else you'll lose the barrier pool on top.

four) use a Seal-a-Meal type device to pull a vacuum on the container to
eliminate as much air in the can as is reasonable.

Other considerations are to ensure the lid is sealing properly to the
container. Metal distortion or cured finish build up on the rim or lid
will cause gaps to allow the entry of air into the container. If you
store the can upside down - and assuming the gaps are small - the finish
will seal the air leaks and stop infiltration. In addition, any finish
that cures at the now "top" of the can will end up on the bottom when
you right it and uncap for use.

You might also buy your varnish in the smallest sizes possible. Paying
less per ounce by buying large sizes ain't a savings if you're throwing
away half of it anyway.

--
Owen Lowe
The Fly-by-Night Copper Company
____

"Sure we'll have fascism in America, but it'll come disguised
as 100% Americanism." -- Huey P. Long