While eyedropping a fountain pen will dramatically increase ink capacity, it also may ruin your pen over a long enough period of time.
It is not recommended to eyedropper metal fountain pens, since the ink will most likely react with the metal of the pen body, resulting in corrosion over time. Some inks will react more than others, but all inks will react to some extent. Stainless steel will be the least prone to corrosion.
Not all metals will be as prone to corrosion, and some inks will be considerably less corrosive as well - so the right combination might make for a decent eyedropper still.
In this article:
Pros and Cons of Eyedropping Metal Pens
Generally speaking, it is not recommended to eyedropper any pen made of metal, since the ink will definitely start wearing away the metal over time. It might be barely noticeable at first but it will show after a while. There are different reasons for corrosion: the most important being the pH-level of the ink, but also its different ingredients.
However, as long as the pen body is one piece, you can actually eyedropper it, as long as you don't care about the probable corrosion - and seal the threads with silicone or an o-ring. The body shouldn't have any caps, rings, or holes which can start leaking once you fill her up.
Another disadvantage is that metal pens will burp a lot more than plastic pens, which can pose a problem with pocket pens especially. Metal pens transfer heat better than plastic ones, which will result in more burping (which means the ink will splurge out of the pen while you write, or, even worse, when it's in your pocket.
Eyedropping is filling the pen body with ink instead of a converter or cartridge. The most important and actually only benefit to eyedropping any pen is the immense ink capacity. Most eyedroppers hold 2ml+ without trouble. Unfortunately, there are more disadvantages than advantages when eyedropping metal pens.
Metals in contact with ink will corrode
The corrosiveness of metals varies, and it will determine how quickly your pen will corrode when in contact with ink. In order to find out which metals corrode the quickest, I've read this study (download PDF) in which the authors research the best materials to use for processing tequila. An apt comparison for our purposes, I think. Tequila has a pH of 3.61, which is as acidic as Diamine Chocolate Brown or Parker Quink Black if I remember correctly from my ink pH testing days.
Least to most corrosive metals:
- Stainless steel
How to Eyedropper a Metal Pen Anyway
All that being said, you can of course do as you please, and it is technically possible to eyedropper a metal fountain pen, as long as the body doesn't have any holes. There are some factors which will greatly increase your pen's life.
- pick the right material
- pick the right ink
- seal the inside with a coating
- Frankensack it
Pick the right material
If you must eyedropper your metal pen, I recommend doing it with either a stainless, or a brass pen. Those are the least corrosive metals, which should result in a way longer life than copper or aluminum pens.
Pick the right ink
pH-neutral inks should in theory corrode metals less, so I recommend picking a neutral ink to minimize damage. I've created a list of pH-neutral inks which you can find here. Or if you're feeling adventurous, you could also check my entire pH database for more than 60 inks.
Some mild inks to try:
- Diamine Teal - pH of 6.9
- Herbin Blue Pervenche - pH of 7
- Lamy Obsidian - pH of 7.6
These inks are basically water (pH of 7) so they should be reasonably safe in theory.
Inks to avoid:
- Pelikan 4001 Black Blue - pH of 2.1
- Diamine Oxblood - pH of 2.6
- Diamine Red Dragon - pH of 2.9
The acidity of these inks lies between a lemon and vinegar, so I can imagine them being pretty corrossive.
Seal the inside
You could try to seal the inside by applying a thin film of some sort of oil or protective layer.
Frankensack it instead
You could also Frankensack your pen, which means you use an old cartridge, and make it bigger using a rubber sack and some shellac.
Other Eyedropper Pens
If you're thinking about eyedropping another (plastic) pen, you should check out my fountain pen ink capacity comparison, which contains more than 50 popular pen models.
Can you eyedropper a Pilot Metropolitan?
A Pilot Metropolitan has a completely encased body, which means it can be converted to an eyedropper. The Metropolitan is made of stainless steel, which means it could corrode over time. However, there's anecdotal evidence that there won't be noticeable degradation. Just make sure to seal the threads.
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