In this short post I'm going to talk about why using the TOMBOW ZOOM 101 fountain pen as an eye dropper kind of works, but in the end it is a bad idea. Let's begin by describing the components of this fountain pen: 1. "nib": this is the metallic piece that touches the paper when you write. 2. "feed": this plastic piece is placed below the nib to provide a consistent amount of ink to the nib by capillary action. It has a grid to maximize its surface, and a canal to allow air into the ink reservoir to gradually fill the space left by the ink as it is used. 3. "inner part of the section": this is basically a plastic cone where the nib and feed are inserted. It has a small hole in the middle for letting the ink flow. 4. "outer part of the section": this is usually when you place your fingers when writing, and it has a thread so that it can be screwed into the body. 5. "body": made of carbon fiber, it's super thin but very resistant, it has a few metal pieces glued to it. One in the bottom for obvious reasons, and another one near the section to allow the section to be tightly screwed with metal to metal contact. This nice touch was probably done to avoid damaging the carbon fiber part of the body. So, what's the difference between an eye dropper vs using cartridges or a converter (which is a refillable cartridge with a piston)? * To place an ink cartridge you unscrew the section from the body and plug the cartridge to the inner side of the section, directly into the previously mentioned hole, at this point you can write with the fountain pen, but we screw the body again to protect the cartridge and so that it has a nicer ergonomics. * To use the fountain pen in the "eye dropper" mode, you fill the body with ink and then screw the section into the body. Note that no cartridge is used here. * With cartridges or converters you can have around 0.5ml of ink, however this pen as an eye dropper can hold about 5ml. The common problem when using fountain pens as eye droppers is that sometimes some pieces of the body are glued, and the ink can unglue them, making a disaster. This is luckily not the case with the tombow zoom 101. Another common problem is that the section-body screws may not provide a fit tight enough to contain the ink. Once again this is not a problem on this pen, because once it leaks a few traces of ink, the ink itself seals itself as it dries. A third problem is that the ink may react with some of the pieces of the body or the outer section, either doing some transformations to the ink or even worse, damaging the pen. This is sadly one of the issues: * After a few months of use, I've seen that the internal aluminum alloy pieces yellowed a little bit and their surface got a little bit rough. * The ink gradually became a paste near the metallic parts. And a fourth problem specific to this pen, is that the seal between the inner and outer parts of the section (3 and 4) is not very tight, and after using it for a little bit it stains your fingers. Finally, there's the issue of the body being so thin and made of carbon fiber (a good thermal conductor), meaning that if the pen is half full of ink, the air inside will get warmer as you use it, thus expanding and greatly increasing the flow of ink, even if you're not writing! In some cases even to the point of forming large drops of ink in the feed and making a mess once they fall. Luckily after doing a good cleanup and going back to a standard size converter, it's working properly again.