Plate XXIX Cetacea c. 1880 is a fine example of chromolithography of it's day. The registration marks in the lower left corner were used to print several stones of different colors. The Chalk Manner can be seen as a crayon drawing on paper. Copyright 1880 by Henry J. Johnson is noted at the bottom of the print. Photogravure Photogravure is a complex yet richly beautiful intaglio technique.
Aquatint photogravure is by far the most common type.
Finely ground rosin or asphaltum was stirred up in a mixing box and the fine dust was allowed to settle on the copper plate. When the dust was melted it created what would become the dot pattern. A sheet of gelatin called carbon tissue was then sensitized to light by soaking it in a solution of potassium dichromate and adhering it to the plate over the rosin or asphaltum aquatint. The plate was then exposed to light through a positive transparency. It was etched in three solutions of ferric chloride producing many different depths of ink reservoir which in turn would print a wide range of gray values.