ALLGEYER’S COLLOTYPE PROCESS.
=Half-tone Negatives= must be softer, and possess more half-tone than
requisite for silver printing. When examined by transmitted light, they
should appear clear in the shadows, and not too dense in the half-tones.
=Line Negatives.=—Negatives for the reproduction of line subjects need
not possess the absolute opacity requisite for silver printing, but the
lines should be clear glass, entirely free from fog or deposit.
=Stripping the Negative.=—The fixed and washed negative is flooded over
with a solution of gum arabic in water (1 to 20), to which has been
added a few drops of a solution of chrome alum (1 to 60). Allow to dry,
retouch with lead pencil, and edge with tallow to prevent overflow,
place upon a levelling stand, warm moderately, and coat with a solution
of gelatine 100 parts, glycerine 15 parts, alcohol 100 parts, water 400
parts, allow to set, and place against a wall to dry, the coated side
outwards, the plate standing upon clean blotting paper. The operation
of drying will probably take a day or two, and when quite complete,
it is again coated with collodion, and again dried. After allowing to
remain in a damp place for two or three hours, cut around the edges
with a knife, and strip off the film, which may then be printed from
either side, and after use may be stored in a book, the leaves of which
consist of smooth paper.
=Reproduced Negatives.=—Coat a plate with a solution of gum arabic 50
parts, dextrine 50 parts, honey 10 parts, sugar 25 parts, glycerine 5
parts, bichromate of ammonium 15 parts, ammonia 50 parts, water 1,000
parts. After drying, expose under a negative, dust over with graphite,
coat with plain collodion, and wash in clean water until all yellowness
disappears.
=Substratum.=—(1.) Water 300 parts, white of egg 300 parts, ammonia
50 parts. (2.) Water 300 parts, gelatine 10 parts, bichromate of
potassium 10 parts. Filter both solutions, and mix, taking care that
the temperature never exceeds 32° C.; pour upon glass plates heated to
30° C., and dry at a temperature of 22° C. After thoroughly cleaning
the back of the plate, place, face downwards, upon a black cloth, and
expose to light through the glass till the coating becomes brownish.
To test if sufficiently exposed, dampen a portion of the film with
the finger, scratch with the nail, and the scratch should stand out
perfectly sharp.
=The intermediate layer= is to ensure the better adhesion to the glass
of the print layer proper, and to facilitate the retention of moisture
while printing. It consists of gelatine 100 parts, water 1,500 to 1,800
parts, alcohol 150 parts, glycerine 5 parts, bichromate of potassium 5
parts. This is spread over the substratum, allowed to dry, and exposed
to diffused light, or allowed to stand for twenty-four hours, well
washed, and allowed to dry spontaneously, after which it may be kept
for weeks.
=The Print Layer= consists of water 1,500 parts, gelatine 100 parts,
bichromate of ammonium 30 parts, complete solution being effected by
means of a water bath; the drying box heated to 45° to 50° C. Place
the levelling stand upon a sheet of white paper, carefully dust and
accurately level the glass plate, and coat, using 30 ccm. of solution
to cover 25 × 35 cm. of surface, avoiding any overflow of solution.
=The Washing Water= used after printing in the copying frame should not
exceed 22° C. in the summer, or fall below 10° to 11° C. in the winter.
Washing should be continued until the film is free from colour, and a
final rinse should be given under a rose. Allow to dry slowly.
=Etching Solution.=—Water 500 parts, glycerine 500 parts, chloride of
sodium 15 parts, or hyposulphite of soda 15 parts.
=Rolling Up.=—If the picture take too much ink, wash off with
turpentine, carefully wipe with a cloth, and continue the etching. If
it take little, wash off the ink with etching fluid, and place in a
hardening solution of chrome alum 1 part, water 6 parts, wash, dry, and
once more etch for a quarter of an hour.
=Varnish for Prints.=—Bleached shellac 100 parts, dissolved in alcohol
300 parts, adding ammonia 300 parts, further adding, with constant
agitation, 600 parts of boiling water.