Most of us are used to the regular fountain pen with a steel or gold nib but that hasn’t always been the only option; indeed it isn’t the only option at present.
The first true fountain pen was a Stylographic with a metal tube and fine wire to deliver the ink to the paper. Stylos remained very popular for many years. Most British pen companies had one of more in their range. During WWII Churchill used a Conway Stewart Stylo.
Eventually they were overtaken in sales numbers by the fountain pen with a metal nib. There are numerous possible explanations for this. The round wire of the Stylo laid down a fine line with no variation. There was no possibility of different tip shapes. The modern drafting pen, essentially the same as a Stylo, has a square cut point but has the same limitations. The pen has to be held near vertically. Those I’ve used have had a tendency to dry up when paused for a few moments but they can use inks not suitable for regular fountain pens.
The other option is the glass nib. I don’t mean those glass dip pens but glass nibs fitted to a fountain pen in the usual way. Such pens were especially popular during WWII when metal was scarce. I’ve had a number of German glass nib pens; most were piston fillers but I’ve also had an inexpensive blow filler. Others including a crescent filler were made in Japan; some were imported into the US under the name Spors. Burnham made glass nib pens too.
The glass nib fountain pen is highly efficient but again, it lays down an unvarying line though the nibs are produced as fine, medium and broad. When used for drawing they can be angled to produce a broad, paintbrush-like stroke.
Though both the Stylo and the glass nib pen are available today they are specialist, not common or widely popular. Why did the metal nib supersede those other types of fountain pen? There’s no one certain answer. There have been periods when line variation was popular and neither of those alternative nibs could produce such a line. The metal nib could also be cut to provide different point shapes, like stub, oblique or italic. For many years gold was the standard metal for quality fountain pens and it had a status that those others did not have. The writing angle of the metal nib is more comfortable than that of the Stylo.
Though no longer the primary means of technical drawing, the drafting pen is still popular with artists, as is the glass nib pen.