A ballpoint pen deposits ink from a tiny rotating ball that rolls the ink onto the page.

The longer version

At the tip of a ballpoint sits a tiny metal ball held in a socket with just enough clearance to rotate. Ink from the reservoir coats the inner side of the ball, and as the ball rolls across the paper it transfers that ink to the surface, leaving a line only as wide as the small patch that touches down.

The ball also acts as a seal, slowing the ink from drying out when the pen is capped. Thick, quick-drying ink is needed so the trail does not smear, which is why ballpoints behave differently from fountain pens. Most writing faults come from a ball that has stopped turning because of dried ink or a scratch on the paper.

Where this entry sits

Odd Little Things looks at the ordinary objects people touch every day and the small mechanisms and histories hiding inside them. Buttons, zips, pencils, mirrors, stairs, stamps, packaging, and road signs all get their turn. The full list sits on the Odd Little Things page, where every entry is listed in order.