How does a fountain pen only consume the ink it needs and does not leak?
In: Engineering
If you look at the ball in a microscope, it has little pores in it that hold a tiny amount of ink. The clearance between the ball and its holder is small enough that the ink doesn’t leak through the gap. That little trick works because all liquids have a quality known as viscosity. You know that honey is very viscous: when you try to pour honey it just oozes slowly. Well, it turns out that all liquids have some amount of viscosity, even ones we think of as not “viscous” like honey. Ballpoint ink is specifically formulated to be just viscous enough to not leak through the gap between the ball and the housing, but able to flow into the little holes in the ball. The ink also acts as a lubricant between the ball and the housing, allowing the ball to spin. If the ink dries out, the ball doesn’t turn, which is why you sometimes have to scrub the ball around a bit to get an old pen to work.
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