The charm of chalk

This week, a video about professional mathematicians’ love for chalk went viral, reaching the top 10 trending on youtube with millions of views within a day of its release.

The video describes the closing down of Hagoromo, the manufacturer of what’s generally considered the best chalk available, and mathematicians’ response to this.

Despite the falling market demand for chalk (quality or otherwise), the closure actually seems as much tied to personal circumstances and the lack of an interested party to take over (although the formulas have since been bought and manufacturing restarted in Korea).

The two most pressing question arising from this story:

Question 1. Why do mathematicians still use chalk?
Question 2. How did this become a top 10 trending video on youtube?

I have little to say on the second question, except for the observations that the video has a high production value and a light-hearted, comical feel, and that the internet is an unpredictable place. [Insert fatalistic remark about the replacement of editorial journalism by poorly understood algorithms.]

But let me remark that there is totally going to be a Simpsons episode where Bart writes something about selling chalk to teachers or some other reference.

Modern teaching

If you are not a working mathematician (or even if you are), the main thing you might be asking is why modern (e.g. digital) teaching techniques have not yet taken over in mathematics.

The answer lies in the teaching demands specific to mathematics and other exact sciences. The material is typically technical and broken down into a lot of small steps. So it’s convenient to have 4-6 boards to refer back to, for example so that you can keep the statement of a result (as well as a picture) up while proving or applying the result.

The biggest problem with slide talks is exactly this: they tend to present information too quickly (and inorganically), and then it disappears too quickly again as well. It is generally considered by mathematicians a great challenge to give a good slide talk, which can only be accomplished by leaving out most of the technical details. This may be appropriate for large audience [non-expert] conference talks, but this is not how you want to be teaching.

Some of the same considerations apply to smartboards. Although you can write in real time (so it’s more organic than slides), the writing surface is small, allowing little content memory. Specific technical annoyances with smartboards are latency, not being able to see what you do, and general technological failure (which is not how you want to be spending your time).

How about whiteboards?

Whiteboards seem to provide a more reasonable alternative. You can still pave a wall in whiteboards to retain a lot of information at once, and the only difference is the material. I even distinctly remember from high school thinking that whiteboards are superior to blackboards in every way, and to have this turned around when I started undergrad.

Some difficulties that whiteboards have and blackboards do not:

  • The surface has too little resistance. Unlike writing on paper, the writing motion on blackboard comes from the arm and wrist and not the wrist and fingers. Whiteboards are sitting in a grey area where there is not enough resistance to accurately write from the arm, but writing from the wrist does not produce big enough characters. RSI is a problem too when you need to restrain your motion.
  • Whiteboards do not erase as well: often they have residue left from previous writing, and an occasional wet cleaning (typically with some chemicals) is needed to clean the board properly. On blackboard, typically a eraser suffices, and if all else fails a wet sponge will do the trick.
  • Whiteboard markers do not indicate their life expectancy. Because there are no exterior signs of a dead marker, they pile up into an unnavigable graveyard of mostly useless markers for you to sort through. With the clock literally ticking as a teacher you don’t want to waste time figuring out which marker to use (and having to go to an office to pick up a new one). Chalk will literally go until it’s a little stump, so it’s much easier to read life expectancy.
  • Whiteboards are shinier, and the reflection negatively affects legibility. (This also applies to lower quality blackboards, which unfortunately I have had to teach on at some point in the past.)
  • Although chalk on your hands (and, to a lesser extent, clothes) is annoying, continued exposure to marker fumes can lead to actual health issues. Plus, marker stains can be hard to wash out of clothes.

Conversely, the main argument for whiteboards over blackboards, as far as I am able to tell, seems to be a dislike of chalk. Admittedly, the feel of chalk on your hands is not great, and if you use a very dusty [low quality] chalk it can get into your mouth as well (which is much more nasty, needless to say). I also found a few people with the opinion that their writing comes out better on a lower friction surface, which is the opposite of what I described above.

Concluding remarks

All and all, mathematicians’ love for chalk on blackboard should not be thought of as an act of conservatism (although mathematicians are rather conservative creatures in some ways ― more in a later post). Rather, it is a product of the teaching challenges specific to the area, and common sense responses to those.

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