With Henderson emulsion I increase to double the quantity.
Further experiments taught me that even if 60 to 80 c.c., and more, of
these coloring matter solutions were added, and the emulsion was left to
coagulate and then laid in alcohol for several days, after which it was
washed well, so that hardly any coloration could be observed, it showed,
when making a copy of an oil painting, that the color sensitiveness of
the emulsion was not reduced, and that it had rather increased in
relative sensitiveness.
Anyhow, I put every colored emulsion for eight days in alcohol, having
experienced that hereby, after washing, just a sufficient quantity of the
coloring matter will remain as is necessary for the color sensitiveness.
For the correctness of what I have said here, the following experiment
made by me will speak:
I mixed with an emulsion a quantity of coloring matter five times
increased, flowed a plate with same, which I then exposed, but obtained
no picture whatever.
The same emulsion I placed for fourteen days in alcohol, washed it well,
and flowed a plate again, which latter had not only the full color
sensitiveness, but almost equaled an ordinary emulsion plate in total
sensitiveness.
From this can be concluded that--as above said--by placing the emulsion
in alcohol, all superfluous coloring matter is removed from the same, and
that only the quantity necessary for the color sensitiveness remains
therein.
Further, it may be mentioned that it might be of advantage to add to all
emulsions eosine besides iodide of silver, because this will give to the
emulsion clearness and brilliancy besides color sensitiveness, and
produce fine lights.
Finally, I express the hope that these communications may be useful to
the practical photographer, and it is my intention to report also about
other coloring matters at some future time.--_H.D., in Anthony's
Bulletin._
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