One of the key differences between fountain pens and ballpoint pens is how they are filled. While ball point pens are essentially a fancy holder for a refill, one can replace only the ink in an empty fountain pen. The process by which this happens has evolved in the century-plus of fountain pens.

They two key methods are either by cartridge or bottle, the latter being the mark of a "self-filling" pen. Cartridges have only become common relatively recently (say, the last thirty years or so), and are generally held in lower esteem than self-filling pens. More on that in a moment.

The earliest fountain pens were filled with an eye dropper. The "section" (holding the nib and the feed) could be unscrewed, and an eye dropper would be used to transfer ink from a bottle to the pen. This got the job done, but was neither neat nor convenient.

Gradually, mechanisms to allow the pen to suck up its own ink evolved. I would say there are two primary classification for post-eye dropper filling systems: bladder (or "sack") based, and piston based. Sack based pens have a small rubber or plastic sack inside of the barrel. The sack is somehow compressed, expelling its contents (air), then released. A vacuum is created, and, if the nib is in ink (or water), it is pulled into the sack.

The earliest pens used a variety of means to compress the sack. One of the more unique methods were pens that had a hole for a user to blow in to (increasing the pressure in the barrel, compressing the sack). However, what proved to be the best way was for a pressure bar to somehow be manipulated to press against the sack. The earliest ones had a slot for a coin or a match stick.

Eventually, two methods evolved that allowed the pen to be self-sufficient. One was the lever-filler, perhaps the image most people have of a fountain pen. A lever on the side of the pen would be pulled out. This pressed the pressure bar against the sack. Replacing the lever released the pressure bar, allowing the sack to expand. This can still be found on pens today (though they are typically quite expensive).

The other method was the button-filler. Under the blind cap would be a button. Pressing the button bowed the pressure bar, compressing the sack. Release the button, the pressure bar straightens, and the sack expands. Though this worked, it typically was higher maintenance than the lever-filler. This has faded.

There were variations on this, including the:

  • Vacumatic filler A diaphragm was moved in and out, pulling ink in the barrel itself. Essentially the same as a sack in principle, it allowed more ink to be held.
  • Touchdown Filling was accomplished by pulling out a tube, increasing the volume of the barrel, which compressed the sack.
  • Snorkel Similar to the Touchdown in design, a small tube extended out the front of the pen. The nib did not actually touch the ink. Ingenious, but quite temperamental.
All of these had some success, though they were somewhat proprietary, and brought with them some issues in maintainability.

The "final" variation was introduced on the later Parker 51s: the areometric. Rather than manipulating the pressure bar through some external means, the front section of the pen would unscrew, revealing the sack and pressure bar. The pressure bar could then be squeezed directly. This was a fairly simple and reliable arrangement. It was first introduced in 1948, and, provided there was no obvious abuse, such a pen is likely to be working today.

Generally speaking, sack-based filling systems have fallen out of favor for all but the very high-end fountain pens. In general, the cost of developing and maintaining such a system has proven to be too expensive.

The other primary self-filling method was the piston filler. Introduced in the fifties, the rear end of the pen was a knob. Turning the knob out would cause a piston to plunge down the barrel, expelling whatever was in the pen (air or ink). Turning the knob the other way would create a vacuum, pulling in ink if the nib were dipped in a bottle. This has proven to be an effective and reliable filling system, and installed on many medium-to-high end fountain pens--probably the second most common filling system available today.

The first? Most low-to-medium fountain pens use a cartridge arrangement. A sealed cartridge of ink is pushed into the section, providing the ink supply. In most cases, a converter is available that allows ink to be drawn from a bottle. These are generally derivatives of either an areometric or piston system.

Of course, this is by no means an exhaustive list--many other ideas have been tried. Parker once made the 61, which made other "self filling" pens look quite manual. The back end was simply dipped in ink, and capillary action drew ink into the pen. More recently, Pelikan created the "Level" system. The pen "docked" with a special bottle that squirted ink into the pen.

Among collectors, self-filling pens are held in the highest esteem, either because it is a vintage pen, or for the retro feel. Converters hold second place, with cartridges tolerated--it's at least better than a ball point.

Sources:
http://www.ettnet.se/~boris/parkerindex.html
The Zoss pen list

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