Blackboard of February 27, 2017, a linear algebra review class.

About Blackboards

Oliver Knill Update July 2020: due to remote teaching, all my course presentations were done from home. Course website. I recorded a short version before class Youtube playlist. Class actually uses both a small board and a tablet, or slides.
Just saw this piece on Slate by Lewis Buzbee. I agree. Blackboards are terrific. It is probably the overwhelming opinion that in mathematics, blackboards are the best tool to develop a thought to a class. They always work and they slow down the speaker enough to get the ideas across clearly. Powerpoint needs lots of restraint in order to be used effectively. It is rarely done right. If people use white boards, then just to write down some key words or a quick drawing. Whiteboards do not work well for complex topics. A white board in the movie "Arrival".
  1. Blackboards always work
  2. It slows the speaker down
  3. They are readable also from far
  4. One can attach magnets
Why are white boards implemented then? First of all, it is cheap and this is always an argument. An other problem is that in many institutions, the people who make decisions about whether to implement blackboards have no idea. They are folks who have seen whiteboards in their seminars and so believe that this is cool. I have taught as a course assistant at ETH Zürich (computer science part), at University of Arizona all classrooms, I taught in were white boards and it had never had a good experience. I had once to give a talk in Vienna, where all the pens were dried out and I had to give a mathematical talk without board. Since then (for example at the extension school), I bring my own pens as backup. Next year, I will bring even my own erasing liquid since the remaining stains are so distracting.

Whiteboards are terrible even for private use. I have had both. During college and also during my postdoc time at Austin, I had a white board on my wall to work on. Since 10 years, have a blackboard at home and love it. Here are some pictures: (from an actual class 2014) (personal blackboard at home 2014) (from an actual class 2010) (Coupled pendulum at blackboard (personal blackboard at home 2009)


A lecture on May 26, 2017. Click for a larger picture.
May 2015 addition: The overhead projector has been popular a few decades ago. I had many classes from primary to high school on this device (probably the majority). One sees the struggle even when great teachers do an example of a lecture by John Milnor in 1965. The pen often does not work well. There is only a small part of the lecture visible. Milnor does the best possible choice with the device. He writes clearly but sometimes, the pen fails to deliver the ink onto the screen. In that MMA lecture (as in many conferences I have seen where overheads were used), there were two projectors used in parallel, a luxury which hardly was available in classrooms.
Slides are used more and more in talks. They are not always used effectively. Most of the time, the talks become too fast with slides. Similarly in lectures. The reason is that the teacher does no more have to think. An other reason is lack of authenticity. Myself in the audience I ask myself, why am I here. I could look at the slides also at home.
  1. Slides make the speaker go too fast.
  2. Slides make the speaker lazy. The speaker does no more need to think
  3. Most presenters have terrible slides skills.
  4. Slides need additional technology (computer, projector) which can fail
White boards often do not work (dry markers), or have old marker traces which are difficult to erase. I had several disasters in this respect. In one conference, there were no working markers any more available and had no communication tool except talking. One also tends to write too small with dry markers and the audience can not read it. In my experience, most presenters do have a horrible handwriting on white boards. Bad writing can be a problem on blackboards too but the chalk does not allow too fast and sloppy writing so that most blackboards are clearer than whiteboards. At last white boards are usually smaller and work only for smaller groups of students therefore.
  1. Markers dry out
  2. Erasing is often problematic
  3. One has to deal with chemicals in the classroom
  4. Whiteboards are usually too small
  5. The presenter writes too fast on whiteboards
  6. The presenter writes too sloppily on whiteboards

White board in the movie Arrival. This is a pretty neat whiteboard in comparison what one sees in offices or classrooms. You see an other whiteboard in room 309 in the Harvard science center. Just open this picture and zoom in a bit to the left. A terrible board even so it has been cleaned professionally.
So, why are white boards or crappy blackboards used? The reason is very simple: administrators who buy equipment often do not teach themselves or do no more teach. Most of the time it is also just simply a financial decision as whiteboards appear cheaper at first.

Here is a blackboard talk on my own larger board at my home office. And an outline on a small 48 x 36 inch chalkboard (a 50+ dollar board). This small board is not bad. It is not of the quality of my large board but much cheaper. One consequence is that one has to wash it off very well in order to erase the previous writing. It would never do in a classroom setting but for having something behind your desk, it is perfect.
Here is a snapshot of my blackboard in the Technion in 1988. The buildings were some "wood houses" where now a larger computer science complex is located. I had doodled around with some surfaces:
A short clip from a This youtube clip of Jake Wright shows a blackboard scene at ETH, showing the Picard's existence theorem for ordinary differential equations.


M4V, Ogg Webm.
June 2019: A nice story showing the obsession of mathematicians with blackboards and chalk:
September 2019: This blog points to a collection of photos by Jessica Wynne on Blackboard photos. Just one sample (which is in a field, I was working in once):
It is a fascinating thing to look at already filled out blackboards. They often are a mystery because the narrative is missing. One of the important points of writing on a slow medium like a blackboard is that there is time to verbally tell a story to it while developing things. Chalk talks are especially good if the speaker did not rehearse it (verbally) or (worse) reads from notes. The reason is that it provides insight into the thinking of the mathematician. This can be lost in slides or written down papers. White boards in principle work too, they are often so hard to read that is is comic. Often one does not see anything. Here is a screen shot from a talk at the Skoltech summer school where one has both white and black boards.

Document history: