Inktend / Pen library / Koloro
Opus 88
Koloro
An eyedropper-filled pen with a shut-off valve, giving one of the largest ink capacities you can buy without switching to a dedicated eyedropper conversion.
A solid mid-range option once someone has decided fountain pens are a habit worth investing a bit more into.
Specs
About Opus 88
A Taiwanese maker best known for popularizing the eyedropper filling system at accessible prices — a shut-off valve design lets the entire barrel hold ink without the leaking risk eyedropper pens traditionally carried. This model — Koloro — dates to part of Opus 88's core eyedropper lineup.
How to fill the Opus 88 Koloro
The entire barrel doubles as the ink reservoir: unscrew the section, drip ink directly into the barrel with a bottle's eyedropper or a syringe, then reassemble. This is the highest-capacity filling method available, often multiple times what a piston holds, but it also means more ink is at risk if a seal ever fails — silicone grease on the threads is essential.
Choosing a nib size
Nib size determines line width, not writing pressure — fountain pens are meant to glide, never press. Extra-fine (EF) suits small, dense handwriting and thin paper; fine (F) is the most broadly recommended default; medium (M) shows more ink character and shading; broad (B) and stub grinds favor bold, expressive strokes and calligraphy-adjacent writing. The Koloro's gold nib will also flex slightly with pressure, giving line variation that a steel nib of the same size won't produce.
Keeping it clean
Because Opus 88 Koloro holds a larger ink reserve, a full flush every 4–6 weeks (or whenever you switch colors) keeps the feed running cleanly. Inktend's cleaning reminder is tuned to a 21-day baseline and adjusts naturally to how often you actually refill.
Pairing inks with the Koloro
High-capacity fillers like this one are the natural home for sheening and shading inks; you'll actually see the color develop across a full page instead of running out mid-paragraph.
Frequently asked questions
More from Opus 88
Specs on this page have been individually verified against manufacturer and retailer listings.