The best portable brush pen for illustration — why this one
The GFKP has a specific reputation in the illustration community: it is not the most expressive brush pen, not the most natural-feeling, and not the most dramatic. It is the most reliable. The nylon tip gives a reasonable line range — fine to medium-broad — sufficient for gesture drawing, cover illustration, comic panels, and journalling. The refillable cartridge means it is not a disposable tool to be replaced when the ink runs out. The price makes experimentation viable. When practitioners move to more demanding brush pens — the Pentel Pocket Brush with its natural hair tip, the Kuretake fountain brush with its ink flexibility — they almost always started with the GFKP. It is the brush pen that teaches brush pen technique.
Refilling with other inks
The GFKP factory ink is Pentel's standard water-based black. The cartridge can be refilled with most other water-based fountain pen inks using a syringe — fill the syringe with ink, insert the tip into the cartridge fill hole, and inject slowly to avoid flooding the brush tip. Pentel does not officially support this, but it is widely done and works well with most inks in the Inkwell range. Flush the cartridge thoroughly with water before changing ink colours. The refill cartridge is sold as a separate variant on this page for those using Pentel's original black.
Honest Note:
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FREQUENTLY ASKED QUSTIONS (FAQ)
How do I change the ink?
Simply unscrew the barrel and insert a new Pentel FP10-A cartridge.
Can I refill the GFKP with coloured inks?
Yes — the cartridge can be refilled using a syringe with any water-based fountain pen ink. Load the syringe with ink, insert the tip carefully into the cartridge fill hole, and inject slowly to avoid flooding the brush tip. Flush thoroughly between ink changes. Pentel does not officially support this but it works well with most inks in the Inkwell range including Dominant Industry, Diamine, and 3 Oysters.
How long does a refill cartridge last?
Variable depending on stroke weight and frequency — a moderate illustrator typically gets several weeks of regular use from each cartridge. The refill cartridge is listed as a separate variant on this page
Is this suitable for calligraphy?
For loose, expressive brush calligraphy where gestural energy is part of the work — yes. For formal pointed pen or broad-edge calligraphy requiring precise line control — no. The GFKP is an expressive tool with a nylon tip that behaves differently from a dip pen nib.