If you ever want to see mathematicians get really excited, ask them about Hagoromo Fulltouch Chalk. Writing on a blackboard with the deluxe Japanese chalk made of oyster shells is “like skiing on fresh powder, or waterskiing at dawn on a calm lake,” says Dave Bayer, professor of mathematics at Columbia University’s Barnard College.

Wei Ho, associate professor of mathematics at the University of Michigan is equally enthusiastic, if less poetic. Hagoromo Fulltouch Chalk, she believes, “writes much more smoothly than any other chalk I have used. I don’t have to think about pressing too softly — some chalk won’t show up without enough pressure — or pressing too hard or squeaking… With other brands, usually after a lecture, my hands — and clothes — are covered in chalk.” It is “especially useful for giving lectures where there’s more time pressure, so you don’t want to waste time and energy thinking about your chalk as you are writing”.

Not all mathematicians, Prof. Bayer admits, care about chalk. Yet it was undoubtedly a bleak day when in October 2014, after 82 years of production, Takayasu Watanabe, the last president of Hagoromo Stationery, decided to close down the company. He cited both his own poor health and “an operating loss” resulting from a decline in sales from a peak of 90 million sticks a year to half that level.

However, he expressed confidence that production would continue, since he had sold the machines for making and moulding the chalk to a local stationery manufacturer and a Korean importer named Sejongmall, and he had plans “to visit South Korea and teach my know-how”.

Many mathematicians aren’t convinced by his reassurances and responded instantly to what one described as a “chalk apocalypse”. “I read in the middle of the night on social media that the Japanese company had closed. I still had a reasonable stockpile, but I went on Amazon and bought every remaining box for sale in the United States,” recalls Prof. Bayer.

Two further developments have cast new light on this hoarding behaviour. Despite teething problems with machinery, Sejongmall is indeed manufacturing the chalk again, which means that it is easily available on Amazon. Prof. Bayer suspects “one can probably tell the two versions of Hagoromo chalk apart, but they are close, and either is vastly better than most alternatives”.

But with the spread of the Covid pandemic, the shift to online teaching has called into question the wisdom of those who thought they were showing great foresight in stockpiling mathematical chalk.

“To be honest,” says Dr. Ho, “I haven’t been at a chalkboard since March 2020.”

Excerpted and adapted from The Economist

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