Question

I agree with the comments from gowers, javier etc. on why blackboards are preferable to PowerPoint and similar media, but I thought that I might try to cover in a little more depth why mathematicians might prefer them specifically to whiteboards: (i) material written on a blackboard is more easily visible, especially at long ranges, and especially compared to text written with a whiteboard pen which is part-way through its lifespan and no longer writes boldly; (ii) chalk is more reliable than a pen: a quick glance at a stick of chalk will tell you how much more you can write with it, but a whiteboard pen can fail at any time, and in my experience too often does; (iii) as they age, whiteboards can acquire a grey patina of accumulated ink which won't wash off; (iv) in my experience at least, whiteboards often just tend to be smaller.