Amateur astronomers sketch what they see through the telescope on black paper. The reason is practical: the drawing comes out the way the eyepiece shows it, white stars on a dark field, with no need to think in reverse. It's a fair summary of what a black paper notebook is for: anything that is light on darkness, and a different way of seeing what you've always drawn on white.
Drawing the light
On white paper you draw the shadows and let the paper be the light. On black paper it's the other way round: the paper supplies the shadows and you only mark what is lit. Drawing teachers use it as an exercise because it forces you to look differently. The classic one is a sphere in white pencil, pressing harder where the light hits and leaving the paper untouched in the deepest shadow.
The idea is centuries old. In 1506 Albrecht Altdorfer was already drawing in black ink with white heightening on colored paper, and the 19th century brought scratchboard, a board coated in white clay and black ink that you scrape to bring out white lines and that illustrators used for decades.
What else it's used for
Lettering and titles, with the same effect as a chalkboard. Night sketches: cities, gigs, skies. Black-page journals and planners. Albums: in the early 1900s family photo albums had black pages, with the photos glued in or held by corner mounts. And anything in silver or gold, which shine most on black.
What it doesn't do well
It's worth saying: a black page isn't better for everything. Studies of reading on screens find that small text is read more accurately dark-on-light than the other way round. For long notes in small handwriting, a white notebook is still more comfortable. On a black one you write larger and fit less on a page, so it suits ideas, titles and diagrams more than transcribing a lecture.
What you write with
Ballpoint ink is dissolved dye and it's transparent, so on black it disappears. What shows is opaque pigment: white, silver, gold and pastel gel pens, paint markers and light colored pencils. We cover it in detail in which pens work on black and colored paper.
What to check before buying one
Most black paper is sold as drawing pads or spiral sketchbooks for artists, from 140 g/m² up, and the black pages usually come inside an ordinary cover. Three things set one apart from another. First, whether the paper is dyed or only printed: you can tell from the edge, and tearing a corner of printed paper shows a white core. Second, how it's bound: a sewn one lasts longer than a glued one. Third, whether it's a pad or a notebook: a pad is for loose sheets, a notebook is for carrying.
Ours is called Nero. It's black all the way through: cover, pages, edges and ribbon. It measures 17.6 × 24.5 cm, has 160 blank pages of dyed 120 g/m² paper, is sewn and comes with a white gel pen.
See Nero, or browse the notebooks in other colors.
Sources: Erika Rix in Astronomy magazine, BBC Sky at Night Magazine, Proko's Drawing With Light lesson, Altdorfer's drawing at the Met, Nielsen Norman Group on light text on dark backgrounds and LancasterHistory on photo albums.