MARBLING

A process of decorating paper or fabric with the result resembling the veins of stone marble. Colors are floated on water, or another medium, and transferred to an absorbent surface by contact. Used in the West since the early seventeenth century, marbling is often performed by hand, but machine-marbled paper is common. 

The first and third example images show books that have marbled paper on boards and marbled page edges. The second example shows a sheet of Cockerell paper.