Ink for fountain pens comes in two major forms: Bottled and cartridges. Cartridges are ideal for the man on the go. The standard European cartridge, which fits all of the pens sold here, is usually about half the size of the barrel of the pen. This means you can store a second one, in case you run out of ink on the go.
Lever fill, piston fill, and various antique fountain pens may require bottled ink. You may also want to try a variety, color, or brand of ink that isn't available in standard size cartridges. In this case bottles are for you. Thepenfountain is here for you, and would like to advise you in your purchases.