Introduced in 1847, the albumen print process was the first commercially viable method of creating a paper print from a photographic negative. It quickly became the predominant medium from the mid 1850s until the turn of the century. The process used the albumen from egg whites to coat paper which was then sensitized with a silver nitrate solution. Millions of eggs were used in manufacturing the paper. Unlike silver prints, albumen prints are not developed but appear through the action of light alone. Subsequent treatments make the image permanent. Because of the smooth surface and the fact the negative must be the same size as the print (no enlarging was possible) albumen prints are incredibly sharp and detailed. They were used to produce millions of wallet sized portraits called cartes de visit (like this Civil War era image), stereo cards, and larger cabinet photographs. Albumen prints have a lovely brownish or purplish color and were usually mounted to stiff boards. Because the halftone printing process had not yet been invented, many late 19th century travel photos were mass produced from the original negatives using the albumen printing process.