"CHROMOLITHOGRAPHY is the name of the process which served in the production of our picture, "The Prize Babies." The word Chromolithography means printing in colors from drawings on stone..."
From: "Epitome of the Process For which the Progressive Proof
Prints in this Volume serves as Illustrations," (Boston: L. Prang&Co.,
Chromolithographs (progressive proofs and prints)
Louis Prang (1824-1909) Prang's Prize Babies: How This Picture Is Made
Boston: L. Prang & Co., 
Print Collection, Miriam and Ira D. Wallach Division of Art, Prints and Photographs, The New York Public Library
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Prize Babies was sold door-to-door by traveling salesmen and
saleswomen. The thirty-eight progressive proof prints (some of which
are shown here) using nineteen separate stones to create the final
image were printed in a limited edition given to those who sold
the most prints, as an encouragement for their successful sales
record. The proofs and the following excerpt describing the process
are taken from the fifteen volumes of Prang scrapbooks held by the
Library's Print Collection.