This channel goes deeply (well, as deeply as is possible) into ballpoint pens, fountain pens, and other writing instruments:

* refills: https://www.youtube.com/watch?v=Pr1UfM8PP0U

* Parker Jotter: https://www.youtube.com/watch?v=6h8uIjfWqm4

* multi-pens: https://www.youtube.com/watch?v=AAJ9BwHKJU4