Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. Photogravure registers a wide variety of tones, through the transfer of etching ink from an etched copper plate to special dampened paper run through an etching press. The unique tonal range comes from photogravure''s variable depth of etch, that is, the shadows are etched many times deeper than the highlights. Unlike half-tone processes which merely vary the size of dots, the actual quantity and depth of ink wells are varied in a photogravure plate and are often blended into a smooth tone by the printing process. Photogravure practitioners such as Peter Henry Emerson and others brought the art to a high standard in the late 19th century. This continued with the work of Alfred Stieglitz in the early 20th century, especially in relation to his publication Camera Work. This publication also featured the photogravures of Alvin Langdon Coburn who was a fine gravure printer and envisioned his photographic work as gravures rather than other photo-based processes.