I bought these and filled them up. Stand them up with the point up, when stored. Application works well, provided you don't hold them vertical (fluid will gush) but lay them down flatter. They work really well. A good strategy is, depending in the shape you want to create, use the pen to deliver the fluid to the location and them shape it with a sharp silicon brush, I made a field of violets for a watercolor painting, and they worked really well. A really ingenious tool, thank you for making them and selling them. We will see how well they hold masking fluid over a medium / long term!