In order to infuse this property in ink manufacturers besides mixing 3.5 grams pigment in each liter of distilled water add 5.0 grams golic acid, 7.5 grams ferrous sulphate and 1.0 gram tartaric acid. The ink of ball pen has to be viscous rather than liquid and should not evaporate like liquid. Therefore, a colorless viscous substance named ethylene glycol is used in manufacture of ball pen ink instead of distilled water. The line drawn by tiny bearing of ball pen is very thin. It does not spread automatically on paper so it does not become bold. To overcome this drawback about 20 times more pigment is used in making ball pen ink as compared with the ink for pen.
The reason for a hole in the nib of a fountain pen is quite elementary and can be gauged with some focused reasoning. Just as tiny ball bearing performs basic work of writing in case of ball pen, split nib performs the work of writing by the pen. As the nib is placed on paper some light pressure that comes to be applied on it slightly widens the split of nib. This phenomenon brings internally stored ink via serrated feeders on to the split of nib through capillary action – and thus writing on paper commences. It is obvious that as the ink comes out it creates vacuum inside pen. The hole on the nib is the tiny window which lets in air to fill the vacuum, because writing can not proceed unless there is equilibrium between internal and external atmospheric pressures.
Ballpoint pen (Wikipedia)
Fountain pen (Wikipedia)