Here is a simpple but very effective lifehack that will allow you to keep a paint fresh for a very long period.
Step 1: How a Good Paint Is Wasted
Most of us who paint have experienced this: you buy a can of good expensive paint, use it on your fence or chair, then close it and put it aside.
5-8 months later you need it again, but when you open the can you see something similar to this photo: the paint has dried up, you can hardly make any use of it.
Step 2: Here's a Simpple Trick That Will Keep the Paint Fresh
I got sick and tired of wasting good expensive paints.
So here's what I came with: I transfer the paint into a plastic bottle. Then I squeeze the bottle untill the paint (or varnish, primer or whathever you got there) goes all the way to the edge of the bottle. Then you screw the cap tightly and leave no air to oxidize and dry your paint.
That's all. Every time you use a little bit of the paint, squeeze the bottle again leaving no air to contact with the content.
Using this simple method I managed to keep a bottle of primer and use it for over 3 years!