The chalk favored by mathematicians

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.


  1. says

    Thank you! I had never thought about chalk, and now have spent the last hour happily clinking through the internet byways of chalk makers, chalk history, the importance of chalk as an article of world-wild trade, artists’ chalk…….What had seemed just a memory of school and university turned out to be very interesting. I shall keep exploring.

  2. chigau (違う) says

    The stuff in the dry-erase pens doesn’t just vanish.
    Like chalk dust, it says on your clothes, hands, hair, etc. Also in the air.

  3. Rob Grigjanis says

    I had a third year (I think it was third) QM prof who favoured chalk of the right length and heft to be thrown at students who weren’t paying attention.

  4. Rob Grigjanis says

    chigau @4: They (me, once) never even saw it coming. He chose his targets well.

  5. raym says

    I recall a physics lecturer at uni (Dr Dr Dr Jones -- he multiple of them), who was ambidextrous in that he would be writing on the board with his right hand, while the left hand was busy erasing what he had written just a minute or two before. There was a lot of scribbling (by students) in his lectures.

  6. blf says

    Similar to @6, I was warned about my Group Theory professor, who — not sure if they were ambidextrous or not — who would write with their right hand whilst standing in front of what they had just written, mumbling incomprehensibly facing the chalkboard, and erasing what they had just stood in front of with their left hand. Occasionally you’d get glimpses of what was just written, blocked from view, described in an mummer, and about to be erased…

    The class was very very small and I’m unsure how many people stuck with it.

  7. Mano Singham says

    When I was teaching, I would first draw vertical columns across the board (the number depending on how wide the board was) and starting from the left, fill up one column before moving to the next. It was only when I filled the last column that I went back to the first one and erased it to reuse.

    This had the benefit that people who came in late did not miss anything, and students could go back and see if they had made a mistake while taking notes.

    It also helped me in that if a student asked q question, I could look back at what I’d written in answering it.

  8. Jenora Feuer says

    I’m reminded of one calculus class I had in University (in 1987) where the professor decided to demonstrate how to prove that ez (that’s e^z if the superscripts don’t come out) was infinitely differentiable over all complex values of z. The room in question had four chalkboards, two at the front, and two on one wall. He’d used all four of them, and had to erase the first one to fill it with a fifth chalkboard’s worth of equations.

    The algebra prof who had the next class in the same room came in, saw the boards, saw our glazed expressions, and went ‘You did this today? I’ll go easy on you.’

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