So I have a library of marker books I've been building, almost all of which have been out of print for twenty to thirty years. I'm gonna put em all online so other people can use them - a few are really uncommon and hard to find! Markers are just straight up NOT TAUGHT in art programs the way paints are, so everyone has to sort of figure it out for themselves... Having freelh available instruction material made by working professional artists from back when these things were king would be really useful I bet
I'm pretty sure I have every marker book that has been published in English that is not specifically about manga style usage, hahaha. Or most of them anyway.