: Yes, you can get spray cans of CO2 (? -or perhaps it's some other inert gas
: that is heavier than air) through Lee Valley tools. You just spray a bit
: in your 1/2 full varnish can before putting the lid on then store the can
: upright. Because the gas is heavier than air it pools above the varnish
: and stops it from oxidizing.

that sounds like a cool idea. Using the same displacem't idea, what about drilling a 3/8in hole in the lid of the can, feeding thru some flex 3/8in tubing(say 8in long - 6in up and 2inside) and tying a balloon on the 2in part. 1/Blow up the balloon just as fitting the lid(got to be just before sealing) or 2/ add 2nd open tube(prob best), and shut lid.

In case 1/ , after closing lid, conceptually don't even have to plug tube(but do it any way. In case 2/, plug 2nd tube for sure and first also for surety.

When the lid is removed, the balloon goes small and therefore most of the varnish pours off it, so not so messy as any of the others.

The problem is the balloon(or condom?)is slightly permeable so the air i/s the balloon will leach slowly into the can. maybe

In case 2/ you could periodically check and blow up the balloon.

stupid ideas!

-mick