Typically, mascara have only 3-6 months before they will harden up and turn into little masses of black coal-like thing, but in case they have turned up like that way before their expiration date:

• Heat water in a pan, put your mascara into the the hot water and instantly your mascara will turn into liquids again, but be careful not to place your tube near the hot surface without water or it will burn your container.
• Also, avoid stirring your mascara wand applicators up and down its tube because it allows more air into the tube and the more it will likely harden up. Because if you notice mascara are placed in an air tight tubes, obviously there is a reason behind that. And now we know.