i used to work as an artists assistant to a calligrapher. he used to have pages of vellum samples like this for reference material. it’s from him i learned the traditional form of drawing celtic knotwork (as opposed to the imitation celtic knotwork found in tattoo parlors)…

kunstwissenschaftlerin: medieval: Large illuminated initial. Smaller initials, rubrics, border designs. (1325-1350) via images.nypl.org