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Should You Use an O-Ring to Convert Your Fountain Pen to an Eyedropper? – Writer's Bloc Blog

Should You Use an O-Ring to Convert Your Fountain Pen to an Eyedropper?

There are many opinions as to whether or not you need to use an O-ring with your fountain pen to convert it to eyedropper fill, so we thought we would share our observations with you.

The main advantage of using an O-ring is that it helps to prevent cracking of the pen barrel. When silicone grease is applied to the threads of the pen barrel to prevent ink from leaking, it is easy to use too much force when screwing the pen back together and this can lead to cracks. The O-ring cushions the barrel, but please do not tighten the pen too much or the O-ring can bulge out!

The disadvantages of O-rings are that they usually are sold in packages containing hundreds of O-rings and it can be difficult to choose the right size of O-ring for each different size of pen. Also, an O-ring alone is not enough to safely convert a fountain pen into an eyedropper fill pen.

We have found that silicone grease is essential to convert your pen into an eyedropper pen, and it will work as a good seal even without an O-ring. For over one year now we have been using one eyedropper pen with silicone grease alone and no O-ring and it has worked just fine without leaking.

The trick is that you need to refresh the silicone grease on your pen every time you refill it with ink. Be sure to coat both sets of threads (on the end of barrel and on the main section of the pen) with a generous amount of silicone grease. When tightening the barrel to the pen after you refill it with ink, avoid using too much force so that you will not break the pen. Wipe off any excess silicone grease. This is a simple, cheap method to convert a fountain pen into an eyedropper pen.

One of our favorite fountain pens that can be converted into an eyedropper fill pen is the Kaweco Sport. The threads of this pen are very close together and it has a generous smooth area below the threads to help give it a good seal when used with silicone grease. Additionally, this creates a large ink reservoir so you can write for a much longer period of time than when you use a standard universal fountain pen cartridge. Do you have any experiences with eyedropper fill pens? If so, we’d love to hear from you!

Without silicone grease, ink seeps past the threads and leaks out of the pen.
Using a generous amount of silicone grease on the threads gives a good seal to your eyedropper pen.
Don’t use too much force to put your pen back together and then wipe off excess silicone grease.
Ink does not seep past the threads or leak from the eyedropper pen sealed with silicone grease.
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6 Replies to “Should You Use an O-Ring to Convert Your Fountain Pen to an Eyedropper?”

  1. The information that you provide in this blog about your products is so helpful!
    I use Kaweco Sport fountain pens (and plan to add a few Kaweco Sport ink rollers to my collection soon) and have converted twelve as eyedroppers using only silicone grease. This has worked on most of them quite nicely using Noodler’s inks. The pens carry much more ink than when supplied with a little cartridge or converter and most behave quite well.
    Three pens showed serious leaking problems, but I suspect the inks, rather than the pens, were the problem. One of the inks was Noodler’s Luxury Blue, which flowed remarkably wetly from the pen and bled through paper that other Noodler’s inks did not bleed through. The other two leaking inks were both my own mixes using the Luxury Blue; they inherited their flow and bleeding straight from the Luxury Blue.
    The Luxury Blue alone has been put into the same pen using a cartridge and is behaving well, with no leaking. The mixes also behaved well, with no leaking, when I put them into cartridges and used the pens.
    Still, nine other Kaweco Sport fountain pens with other Noodler’s inks are functioning quite well as eyedropper pens, converted using only silicone grease. So, I plan to keep them as eyedroppers and use cartridges/converters when working with Luxury Blue.

  2. Thanks for the tip Sheryl! I haven’t used Luxury Blue yet myself, so I’ll have to keep this in mind. I would be interested to know how Luxury Blue performs in a rollerball pen, so if you try it out let me know.

  3. Does the silicone grease react with ink if it mixes inside the barrel? If so, which type/brand of ink is less reactive? Is there a compound about which to inquire with the ink manufacturer?

  4. Very interesting. I did not know you could convert your fountain pen to an eyedropper with an o-ring. I can well imagine that finding the right size o-ring would be difficult!

  5. I have found that plumber’s teflon tape works very well, and even allows multiple fillings with no problems so far. Spool of tape $1 + or – will be lifetime supply. Stops leaks in hose connections with pressure, pen barrel is piece of cake.

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