How long does fountain pen ink last once opened?

Fountain pen ink can remain usable for several years when stored properly. Once opened, be sure to keep the ink bottle tightly sealed and store it away from direct sunlight and heat, which can accelerate evaporation or chemical degradation. A cool, dark environment is ideal. Over time, inks that are not stored properly may exhibit changes in color, consistency, or odor; any of these changes indicate that the ink quality is deteriorating and it might be time to replace it. With the right storage conditions, many common fountain pen inks can last anywhere from 3 to 10 years—or even longer—without noticeable degradation.