Most technical pens are refillable but many use their own compatible ink cartridges that should never be refilled from a bottle but discarded once empty. Inks for reservoir type pens are available in filler bottles. Some drawing inks contain a high proportion of shellac that dries quickly and can clog the fine filament inside the ink delivery system within the nib. The most suitable ink is one that is free flowing but quick-drying, with good adhesion qualities. Some water-based dyes do not have sufficient viscosity for technical pens, causing the dye to flow too freely from the nib and flood the drawing. These should be avoided if possible. There are also pens that are more of the disposable variety that work quite well! Micron Pens, Draftmatics, Koh-I-Noor (shop Pens)and other pens are quite useful as techical pens for drafting.