Esterbrook New Old Stock Ink Cartridges For Twin Cartridge Pen

The original shape of the bottle, which is typified by the long neck with marble, derives from the thirties. In addition to the long neck, the bottle is characterized by the rounded shape and wide, stable base. 

By tilting the closed bottle the bottle neck itself with ink. When righted, the marble will fall vertically and prevent the ink to flow back. This creates a reservoir above the marble which is easy to fill, even if the jar is almost empty.