When I use paints and hardeners when I close a partially used can to be stored to be used later. I use Argon gas from my Tig setup to drive out the oxygen/air out of the container. This stops the paint from getting a skin on top and the hardener from hardening. I have a quick connect fitting in the line between the tank and Tig unit. The flow meter regulates the gas to a slow low pressure flow Argon is heavier so it pushes out the air before I attach the lid or cap on the container. It only takes about 15 seconds of flow to do the trick.
This also works on PVC glue too.
