Mathematicians are hoarding a type of Japanese chalk (2015)
I studied physics and this at a time when faculty gradually changed from blackboard-based lectures to powerpoint. The blackboard-based lectures were far superior to any other way of lecturing (in my view).Main benefit was in the speed of presentation. Writing on a blackboard takes some time, the lecturer is slow enough in presenting that you can really follow along, while not "standing still". What a contrast to powerpoint presentations where the lecturer paused for a minute or two to let students read the equations. Either time was not enough, or you'd start to get bored.Until I graduated at the end of my 5 year program, I tutored freshmen students. Towards the end of my time at uni, they almost exclusively had lectures with powerpoints. I sat in one of the into lectures and what had been a good introductory course to classical mechanics had turned into a mind-numbing powerpoint karaoke show.