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Kosumosu
A premium Japanese ink line named after natural imagery: each color takes its name from a scene like moonlight, autumn leaves, or morning glory.
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Paper & pairing
Reds and pinks show the most dramatic shading of any color family: expect real variation between the edges and center of each letter. This ink will behave predictably on most fountain-pen-friendly paper. Cheap, highly absorbent paper (standard copier paper) will dull any ink's saturation and can cause feathering or bleed-through with wetter nibs.
About Pilot Iroshizuku
Iroshizuku is Pilot's premium ink line, launched to critical acclaim in the early 2010s. Each color is named after a scene from nature, from moonlight (Tsuki-yo) to autumn leaves (Momiji).
Storing and using the bottle
Bottled fountain pen ink has an effectively long shelf life when kept capped and out of direct sunlight: most inks remain usable for years. The main risk isn't the ink spoiling, it's a pen sitting inked and unused for weeks: that's what causes clogs, not the ink's age.
Frequently asked questions
Similar shades By colour distance
Color shown is a close digital approximation of a typical swatch, not a calibrated color match.