Etching is a method utilizing acid and acid-resisting grounds to incise marks into the surface of a metal plate. Those marks are filled with ink, and the top surface is wiped clean. The plate is printed with high pressure on damp paper.
Photogravure is a photographic etching method that produces rich and detailed photographic prints. Photogravure has continued to evolve with digital photography.
Lithography is a method of printing from a chemically treated flat surface, traditionally limestone. Recent innovations utilize aluminum and photo emulsion. All lithographic methods rely on oil and water repelling one another.