Do fountain pens dry out if unused?

An inked pen left idle will eventually dry — the timeline runs from days (poor cap seal, dry climate) to months (Platinum’s Slip & Seal caps famously go a year-plus). A quality cap seal is the whole story.

The habit that solves it: keep only as many pens inked as you actually rotate, store them nib-up, and flush anything going on hiatus. A dried dye-ink pen revives with a water flush; it is an inconvenience, not damage.