I think of the technique as "take away" because your eraser is the "drawing" tool.
In the "Draw!" class I made my first attempt:
|The eraser didn't feel like my friend at this point...|
So this time, I worked larger and because the technique had been altered slightly I was able to infuse the drawing with more intensity. So this is the eraser tortoise*:
|I use all sorts of erasers; some leave behind a LOT of "crumbs".|
It's a messy, smudgy technique but I enjoy it.
* Aldabra giant tortoise photo reference by Peter Chadwick