Invented in the late 19th-century, the ballpoint is now the world's most-used writing instrument. Ink is dispensed through a tube over a metal ball (steel, brass or tungsten carbide) at its tip. The ink is a paste containing dye and oils which dry quickly, although the drying time varies depending on the viscosity of the ink and the diameter of the ball - larger balls dispense more ink and creating a longer drying time.