Some call it the Rolls Royce of chalk, the Steinway of writing utensils. Some say it’s unbreakable, others say it leaves no dust behind.

And it turned the world’s brightest minds into hoarders, going to great lengths just for a few sticks of the stuff.

“I would reach into my cupboard in my office and pull out another box and we’d do the deal in my office,” says math professor (and chalk dealer) Brian Conrad of Stanford University.”

I didn’t want to become a chalk dealer, but I did like the idea that I could be, ‘The first stick is free,’ chalk dealer on the block in my department,” says Max Lieblich, a mathematics professor at the University of Washington.

How did a brand of chalk develop a cult-like following?

For many mathematicians, the act of writing on a blackboard is a type of artistry, one that requires the proper tools.

“It’d be like Picasso using Sharpies on a piece of waxed paper instead of using an actual canvas and oil paints,” says Dave Bayer, a mathematics professor at Barnard College in New York City.

### It’s the math world’s best kept secret

And among the academic crowd, Hagoromo Fulltouch Chalk is the math world’s best kept secret.

“It doesn’t break as easily, and the way it writes just feels right,” says Lieblich.

“It’s like skiing fresh powder,” says Bayer.

“The legend around this chalk is that it’s impossible to write a false theorem using the chalk, but I think I’ve disproved that many times,” says David Eisenbud, a mathematics professor at the University of California at Berkeley.

Hagoromo Stationery first began manufacturing chalk in Japan back in 1932, but it wasn’t until the last few decades that American mathematicians fell in love with it.

“I discovered it when I went to visit the University of Tokyo years ago and one of the professors there … said to me, ‘You know, we actually have better chalk than you do in the States,'” Eisenbud said. “I said, ‘Oh, go on, chalk is chalk … I was surprised to find that he was right.’

“Since the brand did not import into the United States, mathematicians took to ordering boxes online, or through designated “chalk dealers” who began to make a business by supplying the chalk to professors.”

Hagoromo definitely has a cult following, but that cult might be nearly all mathematicians at this point. So it’s a pretty big cult,” says Wei Ho, a mathematics professor at the University of Michigan.

Learn more about the legendary Hagoromo chalk on the latest episode of Great Big Story, a new podcast from CNN about the surprising stories all around us.

### The secret formula remains a mystery

So, what’s the secret sauce? Well, the formula is still a mystery, but everyone has their own hypotheses.

“I assume the special ingredient in Hagoromo is angel tears,” says Lieblich.

“Someone told me that it had clam shells in its compositions … I don’t know if that’s true,” says Eisenbud.

Whatever it is, it was enough to create a deep devotion among its users. The relationship between a mathematician and a blackboard is longstanding.

As Lieblich explains, “the board is like a window into the inner workings of the subject, so going to the board is like going to the magic window … but the only way you really see what’s happening is with somebody writing with chalk.”

The blackboard tradition seems to be beloved among math professors. Bayer describes it, as a “tactile … romantic connection,” one that harkens back to generations of mathematicians that came before them.

“You know, one reads about Archimedes drawing in the sand … but I wouldn’t be surprised if there was something like chalk and a blackboard back then, too,” Eisenbud said.