Some pens come with a converter supplied as standard, but some don't. If you don't have one, you might as well get started with the cartridge supplied. If you have a bottle of ink and a converter, you have the choice.
A cartridge is an easier way to get started with a fountain pen, but if you're only intending to use bottled ink, you can save the cartridge for an emergency and instead start by learning to use the converter. We'll explain how to use a converter later in this post.
A few fountain pens don't use a cartridge or a converter, instead having their own fixed filling mechanism. The Lamy 2000, for example, most TWSBI pens, and Pelikan's Souverän and Tradition ranges, have pistons inside the barrel to fill them with ink from a bottle, and no option to use cartridges. Filling these is very similar to the converter section below, but you don't need to fit the converter first.
There are some other filling mechanisms around, like the vacuum filling systems used in some Visconti pens and the TWSBI Vac pens, but they're fairly unusual.
A cartridge is simply a small plastic tube filled with ink. One end is designed to be pierced when the cartridge is pushed onto the feed. It's usually reasonably obvious which end should be pushed in as it is more 'interestingly' shaped, usually featuring a recessed part where the top part of the feed enters the cartridge, with a tiny ball keeping it sealed. The cartridge fits into place with a firm push, and should 'click' into place. Sometimes they take a firmer push than you might expect, but just need to be pushed straight on, not twisted.
The ink won't start flowing immediately. The black plastic part that extends from the tip of the cartridge to the underside of the nib, known as the feed, is where the ink flows through very fine channels. Because they're so fine, it takes a while for the first ink to make its way to the nib. Sometimes ink will begin to flow in five or ten seconds, but often it will take a few minutes (and some stubborn pens can take quite a while). Just let the pen sit tip-down for a few minutes or so, but if you're going to sit it in a pen pot or cup make sure the cap is in place so the nib is protected.
Once the ink has reached the nib, your pen should be ready for use and you can start writing or drawing. If the flow doesn't seem as good as you'd hope at first, don't worry. Ink flow is sometimes a bit restricted at first, and gradually improves with use.
When the cartridge needs replacing, ink shouldn't take as long to start flowing again, unless it had emptied completely and the ink in the feed has dried out. It's best to avoid this situation, anyway, as dried ink can clog a pen - fountain pens like to be used! If you change to a different ink colour, a lot of the old colour will show up for a while as the new ink works its way through the feed. The ink will gradually fade from the old to the new colour.
If you're starting with a converter, it may already be fitted in the pen. If it isn't, they fit in the same way a cartridge does. Just push the open end onto the back of the feed. There are some converters that screw in instead, but it's quite unusual, and should be fairly obvious if there are screw-threads there.
Almost all converters use a piston - you turn the top part of the converter and a piston inside will wind down towards the open end (towards the nib when it's in the pen). Wind the piston down to the end first. Next, dip the whole of the nib into your ink, making sure it's fully submerged.
Wind the piston back up, keeping the nib fully submerged. Lift the pen out of the ink when the piston is fully up. You should be able to see at this point that the converter is full of ink. If it isn't, don't worry, just try again - you probably didn't have the whole nib and feed in the ink, or the converter isn't properly seated. If you see plenty of ink, but lots of bubbles too, some air was getting in at the same time as the ink.
At this point, many people just wipe the nib to clean off the excess ink, and consider the job done. There's an extra little trick, though, that can help keep your documents, desk (and maybe even carpet!) cleaner. Holding the pen with the nib over the ink, wind the piston back down just a tiny bit. Let around two or three drops of ink fall back from the pen to the bottle. Hold the nib just above the ink, and wind slowly - if turned quickly, some pens can send the ink somewhat sideways. Now wind the piston back up to the top. This pulls a little bit of air back up through the feed, making it less saturated with ink, and it leaves the inside of the converter at a slightly lower pressure. Both of these effects make the pen less likely to drip ink, which can otherwise happen shortly after filling.
Remember to put the cap securely back on the ink bottle, and you're ready to go.
You can see all of the converters we have available, but it's usually best to buy the same brand of converter as your pen. If, however, the pen takes standard international cartridges, it's likely to take any standard international converter. The Faber-Castell converter is good value, and seems to fit a wide variety of pens.
Caring for Your Pen
Now your pen is working, and hopefully you're happy with it, so you'll want to keep it working well for a long time. With reasonable care, most fountain pens can last for many years. Other than trying to avoid dropping it or subjecting it to force, the most important factor in avoiding problems is the ink you feed your pen.
In general, any fountain pen ink should be fine, while anything sold as calligraphy ink or drawing ink is likely to be very bad for a fountain pen. Diamine make a great range of fountain pen inks, in many colours, and they're very safe, but any ink from a known brand should work. Some specialist inks can be used reasonably safely with care, but bring extra risks. These inks are sometimes used for very intense colours or where there's a need for waterproof ink - easy to avoid if you don't need them, but take a little extra care if you do.
If your pen isn't going to be used for a while, it's best to empty the ink out of it so it doesn't dry inside, followed by flushing it through with water by filling and emptying the converter. If you don't have a converter, just soaking the nib and grip section in water will get a lot of the ink out of the feed.
Opinions vary on the flushing of fountain pens that are in regular use. Some say they should be flushed through with water every so often anyway, while others just keep refilling them and using them. Flushing through with water certainly won't do any harm, but it shouldn't be needed if you're using the pen often enough.
For those pens that are in need of a more major clean, Platinum make a cleaning kit, specifically for pens that use their cartridges and converters. For those using most other brands of pen, they have also produced a kit for cleaning pens that use standard international cartridges.