Dr. H.W. Vogel, who was one of the first, though not the first, to devote
attention to this subject, announced, in 1873, that he had succeeded in
making a yellow object photograph lighter than a blue or violet one, by
using a silver-bromide plate stained with coraline, and exposed through a
yellow glass. The plate showed no increased sensitiveness to red, and the
experiment, although of considerable scientific interest, did not
indicate a practically useful process.
In the spring of 1878 I became interested in this subject, and tried to
discover a method of producing plates which should be sensitive to all
colors, and capable of reproducing them in the true proportion of their
brightness. I commenced by trying nearly all the color sensitizers which
had already been suggested, in order to learn which was the best, and
then, if possible, _why_ it was the best, as a guide to further research.
Chlorophyl was the only thing I tried which was sufficiently sensitive to
red to offer any encouragement in that direction; but the solution which
I obtained was weak and unstable, and far from being a satisfactory color
sensitizer. Hoping to obtain a better solution with which to continue my
experiments, I made extracts from many kinds of leaves, and found that a
solution from blue myrtle leaves looked better and kept better than any
other, and when it was applied to the silver-bromide plates they became
remarkably sensitive, not only to all shades of red, but also to orange,
yellow, and green.
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