A ballpoint pen (also eponymously known in British English and Australian English as a biro and pronounced in Britain and Australia but sometimes elsewhere, named after its credited, though contested, inventor ) is a modern writing instrument. A ballpoint pen has an internal chamber filled with a viscous ink that is dispensed at tip during use by the rolling action of a small metal sphere (usually 0.7 mm to 1.2 mm in diameter) of brass, steel or tungsten carbide
Characteristics of ballpoint pens
Pentel R.S.V.P. ballpoint pens.
Compared to rollerball and fountain pens, ballpoints require more pressure to write. Ballpoints lack the free flowing supply of ink that other types have, requiring the writer to apply more pressure to the page. As a result, the ballpoint pens are less likely to leak. Their robustness makes them suitable where a firm press is required, namely for carbon copy-type forms where a layer of carbon paper transfers the writing, but not the ink, to subsequent copies. In such use other types of pens may over time get damaged beyond usability.
They have difficulty writing on surfaces with low adherence (such as plastics, shiny surfaces, and wet or oily surfaces)[12]. Due to the pen's reliance on gravity to coat the ball with ink, most ballpoint pens cannot be used to write upside down; however, there are special pens that do work upside-down
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