91av

I’ve often noticed that after a biro pen has seen regular use, ink seems to coagulate at the nib. This can leave thick deposits on paper that are easily smudged, especially when you start using the pen again after a period of disuse. What is it that causes this to happen? Is it related to any of the chemicals used in the ink?

• It is not purely chemical, but rather a combination of chemical, physical and mechanical effects, depending somewhat on the ink formulation and the quality of the nib’s ball and socket. When stationary, the ball blocks the flow of viscous ink from the reservoir. Drag it over paper and it rotates, picking up a film of ink, most of which it transfers to the paper, and there the ink soaks in and partly dries. Commonly, ballpoint inks contain compounds such as resins that set permanently through drying and chemical reaction.

Especially in low-quality pens, some ink scrapes off onto the rim of the socket as the ball rolls. With a little experimentation in pen holding methods, one may easily see residue develop. Because the residue is soft, unless an alert writer constantly wipes the point, the blob accumulates until it sticks to the paper and smears. A neglected blob on a long-unused pen’s ball, however, might stay put for some time, congealing as it picks up dust and dries out. If still softish, it sticks to the ball and ends up on the paper. Once hard, it does not readily smear, but may jam the socket badly enough to demand brutal scribbling to get the pen working again.

“If the ink blob hardens, it may jam the pen badly enough to demand brutal scribbling to make it work”

Jon Richfield, Somerset West, South Africa