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Opus 88

Koloro

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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

Filling systemEyedropper
Ink capacity~2.5–3 ml (full barrel)
Nib optionsEF, F, M, B (steel or gold)
MaterialAcrylic + ebonite feed
Typical price~$140–170
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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.

Taiwan Founded c. 2015
See all Opus 88 products →

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. Browse the ink library and filter by sheen.

Frequently asked questions

How do I 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.
What nib size should I get for the Koloro?
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.
How often does the Koloro need cleaning?
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.
Is the Opus 88 Koloro good for beginners?
A solid mid-range option once someone has decided fountain pens are a habit worth investing a bit more into.

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Specs on this page have been individually verified against manufacturer and retailer listings.