The exposure through the yellow screen with an erythrosine plate is
about the same as if you had no orthochromatic plate--a plain plate
instead--provided you are not using too dark a yellow on your screen.
This can only be determined by experience. I will give to a common
plate about four seconds, an orthochromatic plate under the same
conditions five seconds.
The yellow glass screen is prepared as follows: Take a piece of best
plate glass--common cannot be used--clean it nicely; take another
large plate glass, or anything that is level and true, level it with a
small spirit-level. Now take the cleaned piece of glass and coat it
with
AURENTIA COLLODION.
Ether 5 oz.
Alcohol 5 oz.
Cotton 60 grs.
The aurentia to be added to suit your judgment; it takes a very small
quantity to make an intense yellowish-red collodion. Pour it on the
center of the glass, flow it to the edges, and before it sets place it
on the level glass and allow it to set; when set put it in a rack to
dry.
Should it dry in ridges, the collodion may be too thick, and it must
be thinned down with equal parts of alcohol and ether. A single piece
of plate glass, about one-eighth inch thick, coated with aurentia
collodion, is all that is required with an erythrosine plate.
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