70 ml of high-quality, general use fountain pen ink from Pilot specifically targeted for plunger-type fountain pens. Each bottle contains a simple but brilliant solution to the age old problem of how to enjoy every last drop of your fountain pen. Plunger type suction fountain pens usually need a certain level of ink to be able to suck up ink into the pen body. In normal bottles, as you approach depleting ink reservoirs it gets more and more difficult to suck up ink. Each of these ink bottles easily solves that problem with a simple plastic tube in the bottle. Anyone who has ever filled a water bottle up and placed it upside down into a bowl will know how the phenomenon works, atmospheric pressure balances out so that the water in the bottle remains higher than the surrounding water in the bowl. In the case of this ink bottle, as the ink levels get low, simply tighten the bottle cap, flip the bottle upside down, and then flip it right side up. Ink levels remain higher within the plastic tube than in the rest of the bottle, allowing you to fill your plunger-style fountain pen with ease. Thank you Japan for the great physics lesson!