Being too cheap for a real fountain pen, but prefering the feel, I ended up with a number of these cheap disposable versions that I found at various places. Problem is that with the amount of writing I do these things last about two days. Therefore I needed to find a way to refill these things cheaply.
For this project you will need a number of items.
Empty Fountain Pen
Fine Grain Sandpaper
Vine Charcoal (charcoal without binder works best)
Small Drill Bit
Jar of Ink (only if you don't want to make your own)
Make sure that you seal the pen very well with the glue. This pen later exploded in my pocket.
Step 1: Opening the Pen
In this step we will be opening up the back of the pen so that we can empty and clean it out. The first thing to do is to pull off this dinky little end cap. A pair of pliers here work well, but make sure that you don't squeeze too hard. While you can still block off the pen, it's easiest to use the cap that's included.
Step 2: Opening the Reservoir
This type of pen has a sealed plastic bubble in the cylinder that contains the ink. A small drill bit would work here, but as I hadn't any on hand, a heated paper clip works as well. Make sure that the hole you punch is big enough for pouring ink into. Try not to burn you fingers on the paperclip either. You kind of need the nerves there to finish the rest.
Step 3: Cleaning the Pen
Unless you know how to make the dame ink color for your pen, you'll want to flush the pen out for your new ink. This is also a good time to check the size of the hole you punched. Bring the pen over to your nearest sink (I'd recommend using a stainless steel sink for this) and rinse it out. If the water doesn't flow through pretty easily you might have to widen your hole. This ink isnt' too hard to flush.
Step 4: Making Ink
Now that you have an empty pen, you'll need some ink to fill it with. While pountain pen ink isn't too pricy (last check about $6 a jar), it would be too easy for this instructable. In order to make this ink, you'll need some art charcoal, rubbing alcohol, fine grain sandpaper, and something to mix these things together in.
In order to get the charcoal into a powder, I used some sandpaper that I had lying around. You could also use a mortar and pestle combination, but I don't have one right now. In this project, we just want to make enough ink to fill the pen, but this can be scaled up fairly easily. Once you have the charcoal ground down, add enough alcohol to make it runny and mix it up. I used a metal chopstick for this step, but anything that isn't wood should work fine. (Make sure that you don't use too much alcohol, because it won't have enough viscosity to stay in the pen.)
Step 5: Adding the Ink
Time to add the ink. For this we'll need a funnel that I don't actually have. Instead, I used this handy piece of aluminum foil.
Wrap the foil so that it forms the basic shape of a funnel and tape it together so that you don't have to hold it. It's important to make sure that it's fairly clear inside so that the ink can flow through. Also important is to make sure that the thing fits into your pen barrel. If not, try again until it works.
The next thing to remember is to let your glue gun heat up before trying to add the ink. It should be plugged in somewhere close to the sink where you can reach it quickly. If you managed to save the cap, you can plug the hole in the end now with a drop of glue.
Once your glue gun is primed, you can pour the ink into the pen. Make sure that your pouring vessel is small enough that you can easily pour it into your funnel. Whoops.
Step 6: Done
Now that you've glued off your pen, you should have a perfectly functioning pen for use with anything you might use a pen for. Note: if the viscosity of the ink is too low, while it will write, it might splatter a bit more than before. Not too big a deal though.