When I started teaching, we used blackboards and chalk. Later, some of the blackboards became green but we still used chalk. The next major change was when the chalkboards were replaced by whiteboards and we needed to use dry erase markers. I had mixed feelings about this change. On the one hand, I used to write on the board a lot and was a messy chalk user. At the end of each class, I would have chalk dust on my hands, hair, and clothes. I would marvel at some of my colleagues who would emerge after a lecture as natty as when they went in. This problem went away with the markers (not an insignificant concern for those with chalk allergies or respiratory issues) but then the problem was that markers would often run dry and the boards would not completely wipe clean without using a special solvent. Also, writing with the markers was not as pleasurable in a tactile sense as with chalk.
All teachers from the chalkboard eras were connoisseurs of chalk, always on the look out to find brands that wrote smoothly and erased easily. There seemed to be a tradeoff. Chalk that wrote and erased easily would create clouds of dust while the smoother polished ones that reduced dust did not write as well or erase as cleanly.
But I had not been aware that mathematicians were particularly sensitive to this issue and that there was a single Japanese brand of chalk, Hagoromo Fulltouch Chalk, that is highly prized by them, so much so that when the company announced that it was going out of business, some professors stockpiled enough of it to last them until retirement.