The reed, before the steel nib
A reed pen or bamboo pen is a writing implement made by cutting and shaping a single reed straw or length of bamboo.
Cutting and shaping: that is the whole of it. No manufacture, no parts. The Van Gogh letters were written with one of these, which is why the stroke in them thickens and thins exactly as a broad-edged calligraphy pen does. A tool anyone can make in a minute, and the hand that used it is the lesson.