Clean those paint tube threads!
Recently I have been cleaning out my paint tube drawer where I keep tubes of oil paint ready to be put out on my palette. I have several tubes that will no longer accept their caps, so the paint dries out!
Here's a tip: I have used the tip of my palette knife to dig through the top layer, only to bend up the tip of the knife making it ineffective at getting a clean line on a painting. I also tried putting screws into the tube hole to break thru the dried layer and this method works somewhat better.
But the real solution is to be more diligent and take more time laying out my paint. After I squeeze a line of paint on to my palette, I dip the end of the tube in solvent and clean it off. This prevents a build up of dried paint, which otherwise makes it difficult to get the cap back on. I believe this method will cut down on my frustration. It takes a bit more time when I’m eager to address the canvas, yet will save me both money and time in the long run.