Dr.
Vogel's new process was not only no better in any respect, but the plates
were insensitive to scarlet and ruby-red, and therefore would not
photograph all colors in the true proportion of their brightness.
[Footnote 3: _Photo. News_, London, September 5, 1884, p. 566, and _Year
Book of Photography_ for 1885, p. 111.]
My method consists in treating ordinary collodio-bromide emulsion plates
with blue myrtle chlorophyl solution, exposing them through the yellow
screen, and then developing them in the usual manner. The emulsion which
I have employed is made with an excess of nitrate of silver, which is
afterward neutralized by the addition of chloride of cobalt; it is known
as Newton's emulsion. I now prepare the chlorophyl from fresh blue myrtle
leaves, by cutting them up fine, covering with pure alcohol, and heating
moderately hot; the leaves are left in the solution, and some zinc powder
is added, which helps to keep the chlorophyl from spoiling. I have a
bottle of this solution which was prepared about six months ago, and now
appears to be as good as when first made.[4] A glass plate is flowed with
the emulsion, and as soon as it has set, the chlorophyl solution is
applied for a few seconds, after which the plate is washed in pure water
until smooth, when it is ready for exposure.
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