Early fountain pens (say, in the late 1800’s) often suffered badly from intermittent flow of ink onto the page, and terrible blotting. It was frequently necessary to shake the pen to get ink to flow down to the nib, but that, of course, risked an unwanted ink splat.
The problem was that the feeds, insofar as they existed, did not allow for smooth ink-air exchange. As explained in the previous post in this series, air has to enter the ink reservoir of a fountain pen to replace the volume of ink that has been written onto the paper. If not enough air enters then the ink flow dries up, and if the air can enter too easily then ink will flow out in drops. It is a key job of the feed to regulate the air-ink exchange.
Possibly the first feed design that successfully regulated the air-ink exchange was patented by Lewis Edson Waterman in 1884.
That patent describes a feed with a channel cut into the top along its full length with fine sub-channels at either side of the main channel.
The patent explains that ink will flow through the finer channels, assisted by capillary action, and when a slight vacuum occurs in the ink chamber an air bubble can enter via the nib breather hole and travel up into the ink reservoir through the main channel. The passage upwards of air would not prevent simultaneous downwards flow of ink because of the natural preference of air for the large main channel and the preference of ink for the thinner sub-channels. In other words, the Waterman feed allowed for a regulated exchange of ink and air and allowed what the patent describes as “a certain and uniform flow of ink to the pen [i.e. nib].” (At that time the part of a fountain pen that we call a ‘nib’ was described as a ‘pen’.
There have been many, many subsequent patents concerning fountain pen components, including feeds, but that 1884 patent of L.E. Waterman was germinal. Most of the vintage ebonite feeds in my collection have capillary channels inscribed in their upper face that resemble very closely what Waterman described, and ebonite feeds are still made like that [link to FPR].
Despite the fact that we call the hole in a nib at the start of the slit a “breather hole”, very few modern pens breathe through that hole! Instead, they have separate air channel that is directly open to the air, usually on the bottom of the feed opposite the nib, and such feeds do not use the 1884 Waterman arrangement to allow contrary air and ink flow. I imagine that there has been many patents relating to the placement and design of an air channel in the feed separate from the ink channel(s), but have not tried to find them.
Even though modern ebonite feeds can have pretty much all of the design features of modern injection-moulded plastic feeds, those features have to be relatively coarse because ebonite is brittle and has to be machined rather than moulded. For comparison, the following photos show details of the plastic feed from a Schmidt FH452 unit (#6-sized). Notice how narrow the ink channel in the top surface is (about the thickness of two sheets of Rhodia paper). A narrower ink channel will have better capillarity than the wider channels of an ebonite feed, perhaps to compensate for the lower intrinsic hydrophilicity of the plastic compared to ebonite. That capillary channel is also very deep along most of its length (about 2mm), presumably to allow more ink to flow through it as compensation for its narrowness. Feed design is like airplane design in that it consists mostly of balancing compromises!
The biggest compromise in many modern plastic feeds is surely the fact that it has to be designed to work with standard international cartridges and converters. That means that the feed must have very narrow spike that fits inside the nipple that goes into the narrow neck of the cartridge. Ink and air have to go through that nipple in opposite directions. The usual solution to that problem resembles the original Waterman patent of 1884, but it seems likely to me that the small diameter of the system at that point acts as a bottleneck to the smooth flow of ink.
If there is such a bottleneck, how can it be that the ink flows without obvious interruptions from the nibs of Platypus pens that use standard Schmidt nib units and cartridge converters? There is a row of fine fins on the plastic feed inside the housing that provides the answer. The gaps between those fins fill up with ink and act as a local reservoir to support ink flow onto the page even when ink flow along the feed spike is impeded by air. In effect those fins act like the ink collector that makes the original Parker 51 so reliable. If you want to see for yourself how much ink can collect inside the feed, simply remove the cartridge or converter from a filled fountain pen and write with it. You might be surprised by how long you will be able to write before it finally dries up.
What’s next?
What’s next in this series is, of course, an explanation of how and why I made my own feeds for the Platypus Model 20 fountain pen!
