The Gentleman Stationer, both the blog and the shop, focuses heavily on practical pen carry, meaning pens that are not just fun to use, but can assist you in getting your work done out there in the real world. I write an ongoing series on what I call “Workhorse Pens,” and I’ve long wanted to do a separate piece on high-capacity pocket pens, which I affectionately refer to as “pocket ink tanks.” While you don’t have to carry these pens in your actual pocket, and many will prefer to carry them in a pen case, bag, or clipped to a planner, the focus is the same: compact, sturdy pens with a large ink capacity that are meant to be used on the go and which will stand up to relatively rough handling.
I’d love to see more pocket pen special releases. Opus 88 does a great job with that. TWSBI used to release semi-regular special editions of the Diamond Mini, but that’s slowed in recent years.
The term “ink tank” is pen-speak referring to a pen with a very large ink capacity, usually with a vacuum or eyedropper filling system. While I enjoy these fountain pens, and they certainly have their advantages, high-ink-capacity pens present their own set of considerations and challenges that you should be aware of before investing in one. That said, I love the ability to ink up a single pen to take on a trip or a long, all-day out-of-office writing session and not have to worry about refilling. I also know that I’m not the only one who becomes easily distracted if I have too many options with me - if I want to focus on getting real work done, I typically like to take 1-2 pens with me and use those exclusively. Ink capacity then becomes a legitimate issue, since I can easily write through 1-2 full converters of ink in a busy work day depending on what I’m doing.
From left: TWSBI Vac Mini; TWSBI Diamond Mini; and Opus 88 Pocket Mini. All three are about the same size.
Considerations When Pocket Carrying: You’ve Been Warned
Relative Fragility and the “Mess” Factor. Put simply, you’re carrying around a plastic tube filled with up to 4ml of liquid that stains (read: “completely destroys”) if the tube breaks. While I’ve never had a pocket fountain pen crack or leak in my pocket, it can happen, and for that reason I wouldn’t recommend carrying these pens in the same pocket or compartment with metal objects such as keys, heavy knives, etc. that could crack or damage the barrel.
You Can’t Avoid the Laws of Physics. If you carry a pen on your person, and especially in your pocket, body heat will raise the temperature of the ink and cause it to expand. Combine this with motion, external temperature changes, etc., and you will inevitably get some ink burping onto the nib and possibly into the cap of the fountain pen. This will be worse in pens you have “eyedroppered” yourself using o-rings or silicon grease, since there is no shutoff valve to keep ink from flowing from the main reservoir (the barrel of the pen) into the cap. Which leads me to….
Consider a Pen with a Shutoff Valve. Personally, the only non-cartridge converter fountain pens that I truly “pocket carry” (i.e., in my actual pants pocket) are vacuum-fillers or japanese-style eyedroppers. Each of these filling systems incorporates a shutoff valve that seals the ink reservoir off from the nib unit, reducing the risk of “inkcident”. If you want to write for an extended period of time, you simply open the shutoff valve slightly to allow the ink to flow continuously. For typical on-the-go pocket pen use, however, such as short lists or notes, you rarely have to do this, as the feed holds enough ink for 1-2 pages of writing at a time.
My Favorite Pocket “Ink Tank” Options
Given the considerations discussed above, what reasonable options exist for a high-ink-capacity, pocketable fountain pen that’s relatively low-maintenance? I alternate a few through my semi-regular rotation.
TWSBI Vac Mini (Top Choice). Because it uses TWSBI’s vacuum-filler system, complete with a shutoff valve, the Vac Mini is my favorite high-capacity pocket fountain pen. It’s relatively easy to fill, holds a lot of ink, and features TWSBI’s reliable stainless steel nibs. The Vac Mini is compact capped, yet it also posts by allowing you to thread the cap onto the barrel. You can read my full review of the Vac Mini here.
Opus 88 Pocket Mini. Those who find the design of the TWSBI Vac Mini or Diamond Mini too understated for their taste might want to check out the Opus 88 Pocket Mini fountain pen, which Opus 88 releases in several different patterns including annual holiday editions. Like most other Opus 88 fountain pens, the Pocket Mini features the Japanese-style eyedropper filling system, so it’s a bit trickier/messier to fill than either of the TWSBIs, but it does feature a safety valve. The main drawback with this pen is that it can be difficult to post - an important factor if you find these pens too short to use unposted. To post the pen with the valve open (as you would need to do to write more than a page), you have to unscrew the blind-cap ever-so-slightly. If you open it too far, there’s no place for the cap to grip the barrel and it will fall off. I will try to have a full stand-alone review of this pen at some point in the future.
TWSBI Diamond Mini. The TWSBI Diamond Mini is similar to the Vac Mini in that it’s a smaller version of one of TWSBI’s standard pens - in this case the TWSBI 580. Like the Vac Mini, the Diamond Mini also posts via a threaded cap/barrel connection. The difference between the two pens is filling system: the Diamond Mini features the Diamond 580’s piston-filler, and while it doesn’t have a shutoff valve, a piston typically works better for pocket carry than a standard eyedropper. (I’m not sure of the technical reasons behind this; I’m speaking solely from personal experience.) I do wish that TWSBI would start releasing both the Vac Mini and Diamond Mini in more special edition colors. You can read my full review of the TWSBI Diamond Mini here.
Three pocket pens, three different nib units, though they all write well, and for the most part, write relatively similar to one another.
Takeaways and Final Thoughts
Personally, given the logistics of carrying around a full 2-4ml vial of ink in my pocket, I’m cautious about what fountain pens I choose to pocket carry. I generally limit myself to sturdier pens such as the three featured here, and opt for pens with shut-off valves like the TWSBI Vac Mini and the Opus 88 Pocket Mini if it’s warm outside or I’m going to be especially active. The TWSBI Diamond Mini is a perfectly functional choice as well. With any of these, you get “all day” (or “all week”) writing capability if you’re looking to work outside your house or office, and all three can be purchase for well under $100, representing good value. As a bonus, all three feature interchangeable nib units specific to these pens, so you can purchase different nib sizes or swap in specialty ground nibs to change up your writing experience. You can’t really go wrong with any of the three options, it comes down to personal preference.
The T.G.S. Curated Shop is an authorized retailer of TWSBI products, including the two pens featured here. While we also sell select Opus 88 pens, we do not currently stock the Pocket Mini, and instead would refer you to our friends at Vanness Pens. This post does not contain paid affiliate links or paid advertising.