Although we're meant to be avoiding adding facial features in order to push the expressive nature of our characters, elements of the nib lend themselves nicely to these features. Notably, the breather hole in the centre acting as somewhat of an eye.
With this in mind, I developed a series of expressive silhouettes, initially sketching them out by hand and then filling them in using Photoshop. Only now have I realised the true power of using a silhouette to convey a specific tone or personality. They've amplified the expressive nature of my initial sketches significantly and allowed me to see what aspects are more effective at conveying a certain expression than others.
My Initial Sketches
The shapes created were influenced both by the stereotypical, medieval court jester appearance and the simple, yet expressive movements of the character Earthworm Jim, as well as referencing Preston Blair's Cartoon Animation book.
I'm very happy with how these turned out (although 'frightened' and 'unhappy' definitely could do with a fair amount of refinement) and it has provided me with a fresh set of thoughts and ideas around how I can bring this fountain pen to life.
Before I came across Kadeem and Phil's suggestion, I had developed a few expressive sketches using the lid as somewhat of a mouth.
Early Expression Concepts
This idea only works in conjunction with expression that comes from the clip (acting as an arm) and the bend and stretch of the rest of the fountain pen (i.e. it's stance). This came from my early commitment to the idea of using the nib as feet, which, whilst its still an idea I'm fond of, is not necessarily the right choice in regards to establishing the character of the fountain pen.