Before storing the oil paint tubes, they need to be clean, especially, the part of the neck where the lid goes. If that part is not clean, they next time we try to open the tube, we might have a hard time opening it. Also, try to clean the entire tube. That's the easiest way to get yourself, your clothes, or anything else dirty or stained.
In any case, if you forget to clean the tube and you're having problems opening it, you can heat the tube with a lighter. Just be careful with the lid since it's made out of plastic.
