To prepare permanent prints from screen-plate pictures,
one must have recourse to one of the tri-color
subtractive methods already described; to utilize these
it is obvious that we must have the three constituent
negatives, but these are not difficult to make. The first
requisite is a set of sharp-cutting filters, the purpose of
which is to isolate each individual color, that is all the
red, all the green, and all the blue. These filters must
be of such a nature that they transmit only the light
of one color. They can be made without much trouble
and as they are not used except as light screens, they
need not be made with such careful attention to parallelism
of surfaces, or cementing, as is necessary in the
case of lens filters. It will in fact be more convenient
to make them the full size of the pictures.
The red filter can be made from two glasses, one coated
with methyl violet and the other with rose Bengal and
tartrazin, or crystal violet and tartrazin. The rose Bengal
filter is made from:
Tartrazin 10 g
Rose Bengal 5 g
Gelatine, 8 per cent solution 700 ccm
The methyl violet is:
Methyl violet 0.7 g
Gelatine solution 700 ccm
The crystal violet is:
Crystal violet 0.4 g
Tartrazin 5.0 g
Gelatine solution 700 ccm

The above quantities are sufficient for i square meter.
It is not advisable to mix the violet with the rose Bengal.
A few drops of glacial acetic acid may be used with both
the violets to facilitate solution. Unless the dyes are used
in the form of a solution previously made, care must
be exercised that they are actually in solution. There
should be no difficulty in this, as they are readily soluble
in the hot gelatine, only, if added all at once, small
lumps of the dyes may become coated on the outside
with chilled gelatine and may therefore not dissolve
well. It is preferable to make the gelatine solution
double strength, use half of the water to dissolve the
dyes, and then mix. The dyed gelatine should be filtered
through linen that has been well washed and wrung
out of hot water.
The green filter must be made with two glasses; one
should be coated with:
Tartrazin 2 g
Naphthol green 1 g
Gelatine, 8 per cent solution 700 ccm
and the other is coated with:
Acid green JE 0.5 g
Gelatine solution 700 ccm
In place of the acid green, 3.0 g of brilliant green may
be used.
The blue filter is prepared with:
Yellowish eosin 4.0 g
Gelatine, 8 per cent solution 700 ccm
3.0 g bluish eosin may be used instead of the yellowish.
The second glass is coated with:
Methylene blue 4B 1g
Gelatine solution 700 ccm