What in the world is suminagashi you're wondering? It's the fancy Japanese word for "the art of paper marbling." It's the method of aqueous surface design (an even fancier way to explain it!) using paints and inks to produce patterns similar to smooth marble and other stone.
This technique has been around for centuries. The oldest examples of suminagashi in Japan, meaning literally "floating ink," are from the 12th century. The trend hit Europe in the 17th century, and the pretty papers were used to line the insides of drawers and bookshelves. Europeans took it a step further by marblings the edges of books.
These images are from the L'Encyclodedie of Denis Diderot and Jean le Rond d'Alembert from 1768. Such fancy rake-tools for creating the patterns!
Whatever you want to call it, it seems to be very in this season with lots of tutorials and inspiration popping up, from pretty stationary to marbled scarves and art work to hang on the wall. Seems like you can marble everything under the sun. This is definitely something I'd like to try.