In college I took a figure drawing summer course. The professor came up from the Savannah School of art to enjoy the Maine summer and teach 3 classes: figure drawing and 2 sections of monotype. In the figure drawing class he carried a simple china marker. He would, after asking permission draw on top of our sketches with his china marker. Je liked them because they wrote over everything, leaving behind a bold line. It also helped that they were dirt cheap. I don't remember what brand he used but he carried a variety of colors, red, blue and black.
A few weeks back I was in Artist and Craftman and found a cup full of them in a variety of colors, around 70 cents each. I picked up a white and a yellow. The yellow is lightfast and I'd assume the white to be as well.
I've been using these on toned pages to add some delicate colors back into my ink drawings. They look a lot like chalk but aren't dusty or smudgey.These are a great way for art journalers to add white to a page when they don't want the look of a ultra fine line pen.
I found multicolor 12 packs on amazon for less than $10.