In 1873 Vogel discovered dye sensitization, a pivotal contribution to the progress of
photography. The
photographic emulsions in use at that time were sensitive to blue, violet and ultraviolet light, but only slightly sensitive to green and practically insensitive to the rest of the
spectrum. While trying out some factory-made
collodion bromide dry plates from England, Vogel was amazed to find that they were more sensitive to green than to blue. He sought the cause and his experiments indicated that this sensitivity was due to a yellow substance in the emulsion, apparently included as an
anti-halation agent. Rinsing it out with alcohol removed the unusual sensitivity to green. He then tried adding small amounts of various
aniline dyes to freshly prepared emulsions and found several dyes which added sensitivity to various parts of the spectrum, closely corresponding to
wavelengths of light the dyes absorbed. Vogel was able to add sensitivity to green, yellow, orange and even red. This made photography much more useful to science, allowed a more satisfactory rendering of colored subjects into
black-and-white, and brought actual
color photography into the realm of the practical. In the early 1890s, Vogel's son Ernst assisted German-American photographer
William Kurtz in applying dye sensitization and three-color photography to
halftone printing, so that
full-color prints could be economically mass-produced with a printing press. ==Other activities==