There is a product called Blox which is an inert gas in an aerosol can which is used to stop paint and finishes from skinning over or drying in the can or bottle. It is heavier than air, and a shot is put in to displace the air in the can on the surface of the unused finish just before replacing the lid.
I do the same thing with the argon/CO2 gas in my MIG welder. I just loosen the wire feed wheels and pull the trigger to dispense the inert shielding gas into paint or finish cans. It works well and is much cheaper than Blox, but not quite as convenient.
