[781]

> “Maintaining a clean whiteboard is much more of a pain,” he said. There’s the cleaning fluid, which costs money, and the chemicals can cause health problems.

A clean blackboard is not that fun either. To clean it nicely you need to sweep the whole of it down vertically with a wet sponge. This requires a water source and it's a messy deal. In high-school there was a daily designated pupil who was responsible for wiping down the boards and keeping a wet clean sponge.

[majewsky]

When I was studying physics, I had a calculus professor who was popular among students for his good use of the blackboard. He would write a ton of text (about 20-25 sqm per 90-minute lecture), but everything was really tidy and well-organized. (He held the same lectures that he gave for the last 20 years, so I guess he got some insane amount of gradient descent going on over time.)

Anyway, for the cleaning, he had a flat mop. The lecture hall had three separate boards, so he used them in rotation. When he was finished filling board A with text, he would wipe board B with his mop while recapping the contents of board A. Then he would rinse the mop and leave it in the sink next to the boards. At this point, board C had dried enough from the previous round of cleaning that he could start writing there again.

Overall, an incredibly efficient and fluent process. The gap in writing gave the students enough time to finish copying everything in their notes or taking a short break to drink something, and it gave him enough time to recap the last 10 minutes before moving on to the next section.

[dsfyu404ed]

>He held the same lectures that he gave for the last 20 years, so I guess he got some insane amount of gradient descent going on over time

I took Calc 2 with a lecturer like this. She had been working there for a few eternities and could probably have taught the wall how to integrate. She had a reputation of being the "easy" professor but after comparing with other students it turned out she actually assigned substantially more work and covered the material faster. Her quality of teaching was just so highly refined that it made the work easier.

[Syzygies]

Professional Korean 70/30 Super Plush 500gsm Microfiber Detailing Towels (16x16, Blue)

https://www.amazon.com/gp/product/B00GXRG64I/

In Germany they outfit classrooms with sinks and squeegees.

Over decades I've tried absolutely everything. I see colleagues in earlier stages of evolution on this (e.g. carrying a squeegee and a bucket), but mathematicians are unbelievably stubborn (think zebra) so one learns not to say anything. This is like debating programming languages: If all parties haven't written significant projects in all languages under debate, just learn to walk away.

Wet or dry, nothing beats a Korean microfiber auto detailing cloth. One or two passes damp (not wet enough to drip while walking) will clean a board better than the overnight cleaning staff. Dry will erase better than any eraser.

[ginnungagap]

In some (maybe most, but my experience is limited to a few) German university they have sinks, sponges and a thing to dry the blackboard after wiping it with a sponge in every class

[nerdponx]

Also the "cleaning fluid" is just isopropyl alcohol

[klodolph]

It is definitely not just isopropyl alcohol. You can verify this yourself by looking at the MSDS. Whiteboards are non-porous, that's an essential part of how they function. The isopropyl alcohol degrades the non-porous layer on top and over time leads to ghosting.

[0xcde4c3db]

I think it's sometimes a mix of several alcohols, but that probably has more to do with ethanol being cheaper than with any issue of suitability or effectiveness. Recently, I've also seen "cleaner" that's definitely not alcohol-based and also doesn't work worth a damn.

[gnulinux]

Is inhaling small amounts of isopropyl alcohol safe? I found conflicting information online. Apparently it's also used for pipe and vape cleaner.

[klodolph]

For questions like these, I would start with the MSDS. While the MSDS doesn't always answer your questions, they tend to be reasonably conservative relative to typical use. For example, they sometimes recommend safety gear that people ignore.

Keep in mind that isopropyl alcohol is available at different concentrations, and the different concentrations have different MSDS. Here are the hazard / precautionary statments from the MSDS:

H335 - May cause respiratory irritation P261 - Avoid breathing mist, vapors, spray. P271 - Use only outdoors or in a well-ventilated area.

Note that "avoid breathing mist, vapors, spray" is not an especially strong statement.

[EamonnMR]

https://en.wikipedia.org/wiki/Isopropyl_alcohol#Safety

Yeah.