Why Chalk?

As schools work to phase out dusty chalkboards en masse in favour of shiny new whiteboards, interactive whiteboards or projectors, there is one group of people clinging on to the old fashioned way of doing things with dear life: mathematicians.

So why chalkboards? What is it about chalkboards as a teaching tool that justify using them in this modern day with modern tools? I've tried to condense here a few key ideas as to why chalk is, in my opinion, the best tool for teaching and learning mathematics.

Presenting an effective lecture is about telling a story. Developing the machinery required for a complex proof in a lecture can be a long process, which requires many steps including some motivation, setup and many auxiliary results. When presented with an empty blackboard and a piece of chalk, a lecturer has to engage and think deeply about the material they are teaching; presenting new ideas in the way that makes the most sense to the audience and leaving out no details. On the other hand, pre-prepared slides encourage the speaker to be lazy and not engage with the material themself while teaching, which results in less clarity within explanations. They do not show the order and process of thought. When drawing a diagram in front of an audience, the layers of the image can be built up piece by piece, showing how one element follows from the other. This is why viewing the final state of a blackboard after a lecturer misses so much important detail. On a blackboard a lecturer can leave gaps and fill them in after the fact, returning to earlier content and adding details when they fit the overall narrative.

Writing new things on the blackboard potentially not in a top-to-bottom left-to-right order shows the material being introduced in the way it is thought about. Anyone who has taken introductory analysis will know that sometimes the way a final proof is written can be backwards to the way it is reasoned through by the author.

In this sense, a lecturer forcing themself to write everything down on a blackboard slows them down. This effect is very real, and very important. When compared to teaching from slides or pre-prepared notes, there is no question: teachers who use pre-prepared notes and talk over them, no matter how hard they may try, move through the material faster than many students can keep up. Forcing the pace of teaching to be no faster than the pace of writing is crucial to delivering material at a pace that students can follow.

Many large lecture theatres will have many blackboards on sliders which can be moved up and out of the way, but still visible to students. This allows students to spend additional time looking over and thinking about the material from earlier in the lecturer if they need it. Very often teachers who depend on slides will leave students behind if they're still looking at material from a previous slide after the lecturer moves on.

Okay, but so far this case has been built on the comparison with teaching from slides, but what about whiteboards? Indeed, I also think whiteboards are a far inferior teaching tool.

A piece of chalk and an erasing cloth is all you need to write on a chalkboard. This reduction in interruptions and startup cost allows a lecturer to begin teaching immediately, a benefit which is certainly not provided with overhead projectors, document cameras, or slide shows. Even when working with a whiteboard, the constant drying out of markers results in a non-trivial amount of time spent working through old markers which leave impossibly faint lines.

Chalkboards have a pleasing resistance that prevents the sloppiness that comes with a slippery whiteboard. In my experience almost everyone's handwriting is naturally neater on a chalkboard, rather than a whiteboard.

Whiteboards are glossy, and the glare they produce, combined with the stains from poorly erased previous uses make whiteboards difficult to read, especially at a distance in a large lecture theatre. Blackboards also consistently show up better on video, a feature which is especially important in the post COVID era where everything gets recorded for the benefit of distance learning students. Much of the disagreement I have heard with respect to this point comes from people who don't know how to clean a blackboard properly, so as a PSA I will mention, a quick wipe from a slightly damp cloth will get a chalkboard completely clean extremely effectively, moreso than cleaning solution and a lot of elbow grease will on a whiteboard that has been left for more than a couple hours.

So if chalkboards really are so much better than the alternatives, why are fewer and fewer people using them? Well for one, good quality chalkboards are more expensive, and unlike whiteboards, it is harder to get away with the cheapest option. However, more importantly, I suspect some readers right now may be recalling traumatic memories of their time in primary school with dusty and dirty chalkboards, and the horrible sound of someone scraping a piece of metal across them (it makes me wince thinking about it too). It is at this point that I need to inform you that porcelain enamel chalkboards written on with that buttery smooth Hagoromo chalk and cleaned with a damp microfiber cloth make for a dust-free, clean chalkboard experience, with extremely clear and readable lines. This is a chalkboard experience most people have unfortunately been deprived of. As such, in practice, my experience working with a chalkboard looks much more like this.

picture of beautiful chalkboard showing the proof of lagrange's theorem

So please, if you are a university administrator, or wield any decision making power with respect to teaching equipment: while I realise chalkboards are not for everyone, there are many of us who love chalk and can't imagine having to use anything else, and the experience of using chalk is not always as it is made out to be.

Equipment

For anyone wondering, my recommended blackboard equipment is Hagoromo for chalk and microfiber detailing cloths for dusters. If you are interested in getting a chalkboard, the thing you are probably looking for is a porcelain enamel steel backed chalkboard. Unfortunately I don't have any particular recommendations, as good chalkboards are increasingly difficult to get for individuals, but if you know of a university near you with a sufficiently large mathematics or physics department they might be able to let you know their suppliers. If you live in central Europe, I hear schultafel.de is a great brand which sells to individuals (although I have personally never tried one). I got my board from the university at which I am a student, since some renovations meant they would have otherwise been disposed of.

Why Chalk?

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