What is a lithographic plate?

Polyester litho is a thin paper-like sheet with a coating on one side that resembles a stone surface and which can be printed from using relief ink. Once a print run is finished the plate itself is a reversed image of the prints. It often has marks and textures resulting from the printmaking process, which I particularly like as it adds to the depth of the image. These plates have their own character, subtly different from the print, and so become a piece of art in their own right even as they formed part of the process.