Inktend / Pen library / Calamus
Aratrum
Calamus
A model in Aratrum's fountain pen lineup. Specs below reflect the typical configuration across Aratrum's core range.
A solid mid-range option once someone has decided fountain pens are a habit worth investing a bit more into.
Specs
About Aratrum
Aratrum is a German writing-instrument distributor that has been in business for more than two decades, known among other things for hosting Kaweco build-your-own-pen events. In 2021 it launched its own CALAMVS line comprising a fountain pen with built-in piston converter, a ballpoint and a rollerball.
How to fill the Aratrum Calamus
Fill it two ways: snap in a pre-filled international cartridge for convenience, or use a converter — a small plunger or twist mechanism that installs the same way a cartridge does — to draw ink from any bottle. The converter route opens up the entire world of bottled ink, which is where most of the hobby's color variety lives.
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.
Keeping it clean
A quick flush with cool water every time you switch ink colors — and a full clean every 4–6 weeks of regular use — is enough to keep the nib and feed performing well. Inktend's cleaning reminder is tuned to a 21-day baseline and adjusts naturally to how often you actually refill.
Pairing inks with the Calamus
Because refills are quick with a cartridge or converter, this is a good pen for rotating through several colors rather than committing to one; sample vials work especially well here.
Frequently asked questions
More from Aratrum
Specs reflect the typical configuration across Aratrum's core lineup rather than this exact model — check current listings before buying.