Ebru Art (or Paper Marbling in English) is defined by wikipedia as:
Paper marbling is a method of aqueous surface design, which can produce patterns similar to smooth marble or other stone. The patterns are the result of color floated on either plain water or a viscous solution known as size, and then carefully transferred to an absorbent surface, such as paper or fabric. Through several centuries, people have applied marbled materials to a variety of surfaces. It is often employed as a writing surface for calligraphy, and especially book covers and endpapers in bookbinding and stationery. Part of its appeal is that each print is a unique monotype.
In the next two videos we can see it in action: