Certain paint pens must be primed when they get used for the first time or after they have not been used for a long time. They need a really good shake. Some of the pens have a ball inside to help the paint get mixed when you shake them. The nib can be pressed down to get the paint flowing. It’s best to always prime the pen on a piece of scrap paper and not on your work. Always check the product’s instructions on how your pen needs to be primed.