- I assume the special ingredient was angel tears.

- Mathematicians from all of the top schools very frequently use it.

- It's a cult favorite.

- As soon as I use it I was a convert.

- The chalk is one of the best kept secrets in the math world.

- It's the Rolls Royce of chalk.

- Hagoromo is a brand of Japanese chalk.

The way it flows on a board is a bit hard to describe in words.

- It's really hard to get.

You can only get it from Japan, you need a Japanese person to bring it back for you.

- I discovered it when I went to visit the University of Tokyo and one of the professors there said to me, you know, we have better chalk than you do in the States and I said, oh go on, chalk is chalk.

And so I tried it out, and I was surprised to find that he was right.

- I tried it, and I thought it was phenomenal.

It's the densest, it erases the cleanest,

it leaves the nicest line.

- If you use bad chalk often you have to press really hard for anyone to see what you're writing so using Hagoromo on a good board, it doesn't really feel like you're working hard to write.

- When I'm teaching I get a feeling of energy, confidence, and the chalk absolutely helps.

- Slowly the math world has become aware of this, and it became a bit of a fad in some circles.

- It was like maybe four years ago the word came out that the company was going out of business.

I sort of jokingly referred to it as a chalk apocalypse.

So I immediately started hoarding up as much as I could.

- I ordered three boxes of Hagoromo and kept it in my office and used it very sparingly.

- I should've bought more but I have friends that bought boxes and boxes and boxes of the stuff.

They might very well be set for the rest of their career.

- We've got like 1,500 sticks.

That's a lot of days, four sticks a day.

I think I'm gonna make it.

- I have probably a 10-year supply still at home.

- I calculated how many boxes would I need to last for 10 or 15 years.

I didn't wanna 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.

- I was probably selling it regularly to maybe eight to 10 colleagues.

I would reach into my cupboard in my office and pull out another box and we'd do the deal in my office.

Yeah, we all had a chalk fix.

And we still do.

- The original Hagoromo chalk is slowly disappearing.

A few years ago, a Korean company bought their formulas and did the best job of faithfully reproducing it in Korea.

- It was mixed emotions.

I was happy to know that it would still be made.

But I was a little disappointed that I was less clever than I thought I was.

- In many ways mathematics is like craftsmanship, in some ways it's like artistry; in some ways it's like science.

But there's a real high craft side to getting a beautiful lecture on a blackboard.

Mathematicians admire this in each other and like to use the best tools for it.

- There's incredible value to this but the value is in using it up, not hoarding it.