Diplomat Nexus Review: A Fountain Pen With a Sealing Twist

Introduction

Every so often a pen maker tries something genuinely different, and the Diplomat Nexus is one of those attempts. Launched about a year ago, this fountain pen blends an eyedropper-style ink chamber with a section that seals itself when the cap goes on. It looks striking, it feels substantial, and it fills a huge ink capacity thanks to the included pipette and ink bottle. After spending time with the unboxing, the filling process, and a proper writing sample, here is how it all comes together.

Design and Build

The Nexus arrives in an unusually large metal box with a sliding top, which includes the pen, a bottle of Diplomat Royal Blue ink, a large pipette, and genuinely useful instructions. The pen itself is available in solid blue, black, and green, plus clear-barrel versions in black and blue. The chrome cap and trim sit over a transparent barrel, and the blue clear version is particularly striking, though the polished chrome does attract fingerprints and needs an occasional wipe.

The pen has real heft. It feels very solid in a quality way, more like a heavier metal-bodied pen than something fragile. The clip has decent strength and works across a variety of materials, with Diplomat’s cut-out ink drop logo letting the barrel color show through, which is a neat design touch. The barrel is straight with only a slight transition where the cap meets it, and the Diplomat logo and numbering on the barrel look sharp. The pen is said to be a limited edition, though the exact production count is not documented anywhere we could find.

The Unique Sealing Mechanism

This is the Nexus’s party trick. It is not a vacuum filler, but it borrows from the traditional Japanese eyedropper approach: a rod inside creates a separation, essentially a seal, between the section and the ink chamber. What makes it unique is how that seal is managed.

The section itself moves. When the pen is uncapped and in use, there is an opening between the ink barrel and the section, so ink flows freely with no need to crack anything at the back. When you cap the pen, capping pushes the section down and compresses a spring in the back, which seals off the section from the ink chamber. That seal helps keep the ink from drying out and makes the pen safer for travel. It is a practical solution to an eyedropper pen’s usual weakness, and it is executed in a way we had not seen before.

The section is metal with slight grooves to add grip. It angles up just a little and transitions into large, blocky threads through a stair-step detail, creating a continuous line pattern from section to threads that looks intentional. Even so, the section sits right on the edge of being slippery; a more concave shape would have helped. There is a small step up to the barrel, and an o-ring inside helps seal the section when it is installed.

Nib and Filling

Under the cap sits a number six stainless steel nib available in extra fine, fine, medium, or broad, paired with a plastic feed. The review unit came in extra fine, which is not a size we test often. The cap twists off in just about one full rotation.

Filling is an event. You remove the section and seat it upside down in a compartment of the included container, so any ink residue drains into the plastic rather than your desk. The barrel goes over the ink bottle opening, and the included pipette, which is genuinely enormous, draws a full load and releases it into the barrel. One pipette fill took the chamber essentially to the brim. It is overkill in size, but it makes filling quick and mess-free.

Writing Performance

The extra fine nib was a pleasant surprise. First, the capillary action is excellent: unlike a cartridge setup where ink has to work its way down slowly, ink reached the section quickly on first fill, impressively fast for a pen of this design.

The nib is not scratchy, but it does have a fair amount of feedback, especially for an extra fine. It is not glassy-smooth, but the feedback feels pleasant rather than harsh. Ink flow runs a bit on the lighter side, which is appropriate for a fine point. Fast writing is handled well, with the feed keeping up comfortably. Reverse writing catches a little and feels scratchy, so that is not its strength.

The included Diplomat Royal Blue ink is a good match for the pen, and on heavier applications it shows some nice shading. Other royal blues vary noticeably: some lean more purple and saturated, others lighter, so there is room to experiment once the included bottle runs dry.

Size Comparisons

The Nexus is a large pen. Next to other Diplomat models like the Excellence A, the Arrow, and the Eloquence, it sits noticeably bigger. Compared with non-Diplomat pens such as the Platinum 3776, the Montegrappa Venia, and the Delta Dolcevita, it reads as a full-size pen both capped and uncapped. If you prefer compact pens, this one may feel oversized; if you like substantial pens with presence, it fits the brief.

Buying Advice

At $316 from a wide range of retailers, the Nexus is not cheap, but it does not feel overpriced either. It is very solidly built, brings a genuinely unique mechanism to the table, and includes useful accessories that make an intimidating filling system approachable. If you want a high-capacity pen with a design you will not find elsewhere, and you are comfortable with a heavier pen and a nib with some feedback, the Nexus earns its price. If you prefer light, smooth-writing pens or dislike fiddly maintenance, more conventional options will suit you better.

Conclusion

The Diplomat Nexus succeeds because its unusual mechanism serves a real purpose rather than existing for show. The self-sealing section solves the classic eyedropper problem, the huge ink capacity and included pipette make filling practical, and the build quality feels premium in the hand. With a few trade-offs around the slick section and a feedback-heavy extra fine nib, it is a distinctive, well-made pen for anyone who wants something a little different in their rotation.