A type of blackboard chalk that was produced for decades by just one factory in Japan was so highly prized by mathematicians they referred to it as “the Rolls-Royce of chalk.”

And when rumors surfaced about the chalk being discontinued, some academics resorted to stockpiling as many boxes as they could get their chalk-covered hands on…

Hagoromo made chalk for more than 80 years, and for those who weren’t lucky enough to live in Japan, Fulltouch was always difficult to get. Then, as Hagoromo prepared to shut down in 2015, many dedicated aficionados began grimly preparing for a world without Fulltouch. They bought dozens upon dozens of boxes, some hoarding enough chalk to last through the end of their careers…

…The chalk is long-lasting, virtually unbreakable, bright and easy to read on a chalkboard, smooth as butter to write with, and practically dustless, Jeremy Kun, a Google engineer with a Ph.D. in mathematics, wrote in a 2015 blog post bidding farewell to Fulltouch.

There’s a video heading the article. So renowned is the chalk among mathematics professionals that it is accompanied by its own legend: It is impossible to write a false theorem with it, David Eisenbud, director of the Mathematical Sciences Research Institute in Oakland, California, says in the video.