My Rotring Art Pen was the first cartridge drawing pen that I had, and my dad gave it to me in high school when he started teaching me how to pen and ink. It was perfect for learning control of line weight and always glided on the paper. When I finally got it out after far too many years sitting in an artbox, I found that the cartridges I had left were only half full (or half-empty?) and thanks to the evaporation the remaining ink was too think to flow. I decided rather than buying my own cartridges- I’d refill them myself. I got a pack of 6 vet syringes and was able to load the cartridges with Rapidograph Ultradraw, once I had cleaned them out. Now it’s fully functioning and ready for my sketchbook- but I think I need to experiment more with some hypodermic needle drawings.