FAILURES IN COLLOTYPE.
IN THE PREPARATION OF THE PLATES.
=Air bubbles= in the albumen substratum. These must either by
filtration or by the aid of a piece of paper be carefully removed from
the solution before it is applied to the plates. The latter must be
well cleaned and dusted, and freed of emery powder if they have been
re-ground.
=To Prevent Dust= or other matter rising from the edge of the plates by
capillary attraction while standing, they should be allowed to rest on
clean blotting paper, and preferably on one corner only.
=Coating Plates.=—Great difficulties are experienced by the beginner
in coating the plates with the chromated gelatine. He seldom knows
beforehand the exact quantity required, or the temperature of the
solution. The latter ought to be ascertained, as it is an important
factor in the thickness and flow of the coating; with a solution only
just warm it is impossible to apply a very thin coating, while the
hotter the gelatine the thinner the layer. Considerable dexterity
and judgment are necessary to spread an even layer of the requisite
thickness, which is a matter most essential to success, but,
unfortunately, only to be mastered by actual experience.
Plates are not unfrequently spoiled by inclining them while conveying
them to the drying box, as in this way the coating is frequently
rendered uneven.
All solutions must be carefully filtered, and the plates freed entirely
from dust. The drying box, particularly the lid, must be carefully
dusted and cleaned, but not immediately before use.
Other necessary precautions have been pointed out while describing
the preparation of the plates. By strictly adhering to the rules laid
down it will be found possible, after a certain amount of practice, to
avoid the pitfalls here enumerated, while with regard to faults in the
plates, there only remain to be mentioned the consequences of drying at
too high a temperature.
=Thick Films= are extremely liable to fly off the glass and damage its
surface, if dried at too great a heat. The thicker the film the lower
should be the temperature of the drying box.
=Thin Films=, dried at too high a temperature, even without exposure to
light, present a brown appearance, their sensitiveness is impaired, and
they take too much ink over their entire surface.
FAILURES IN PRINTING.
It is generally an advantage to work the press in a cool and somewhat
damp apartment.
=Breakage of the Plate.=—Notwithstanding its thickness, the glass
plate sometimes flies to pieces on pulling the first impression. If
the plate and its foundation are perfectly level the breakage must
arise from the presence of some foreign substance having found its way
between the two surfaces.
This may occur from such a trivial matter as a grain of sand, perhaps
introduced between when moistening the under side of the plate to
secure adhesion. Or traces of chromated gelatine may be found attached
to the under surface of the plate, either of which causes is quite
sufficient to account for a breakage with even moderate pressure.
In Collotype the pressure need not be by any means so heavy as in
lithographic printing; it should be evenly distributed, and may
be moderated by placing the stone or glass plate, or whatever the
Collotype plate may be attached to, on some comparatively elastic
bedding, which may consist of several layers of printing paper, thin
felt, thick indiarubber sheeting, or linoleum, any of which may be used.
=Spotted Impressions.=—The plate yields unsatisfactory copies covered
with white spots resembling drops of water. This most frequently occurs
at the commencement of the printing, and is nearly always caused by
uneven damping of the surface. Old plates which have been dried very
often give perfect negative impressions at first. In such cases, after
the removal of the ink by turpentine, soak the plate for a quarter
of an hour in water, to which has been added a little glycerine and
ammonia (see “Etching Fluid”). Dry the plate with a clean roller
covered with cloth or chamois leather—or, as a substitute for the
roller, a soft linen cloth may be used—and again roll in with ink which
has been thoroughly well distributed on the inking slab.
=Too Much Ink= is taken by the plate over the whole surface, and
notwithstanding slow or rapid rolling, it refuses to leave the high
lights. Cause—over-exposure in proportion to the thickness of the
layer, which is probably too thin. In such cases washing with dilute
solution of ammonia will often improve matters. Another proceeding
to be recommended in the case of a plate taking too much ink is to
remove all ink by means of a sponge damped in water containing a little
petroleum—not benzine or turpentine—and afterwards wash the plate with
a sponge containing glycerine and water. It is then ready for immediate
printing from, and ought to give about 200 copies without further
damping if the press be in a moist situation.
=Loss of Half-tone= arises from the print layer becoming too moist,
when the more delicate half-tones fail to print. Dry with blotting
paper, and immerse for five minutes in a bath of alcohol; this will
take up the water, and the succeeding impressions will be greatly
improved.
=Uneven Inking.=—It sometimes occurs, particularly in pictures which
should show a white ground, that the latter takes more ink in one part
than another. This usually arises from an unequal thickness of the
sensitive coating. The plate will take most ink where the coating is
thinnest, and for this fault there is no remedy.
=Ink Refused by the Plate.=—Sometimes, after a few impressions have
been pulled, the plate refuses to properly take the ink, from the layer
being too thick and having been too freely moistened. Further damping
should be discontinued and a thinner ink used, which will better take
upon the deep-lying shades. This fault will be found most pronounced
in the cases of written or printed titles to pictures, and other cases
exhibiting extremely disproportionate action of light. Therefore, when
there is writing to a picture, it should be shaded somewhat during
printing in the printing frame, or if the contrast be very violent it
may fail to print entirely.
=Flat Prints.=—After a number of satisfactory prints have been produced
the succeeding ones become flat, this fault will be especially
noticeable with thin layers devoid of isinglass, and in cases where the
negative has been too flat and lacked contrast. Dampen more frequently
with dilute ammonia and glycerine.
=Paper Adhering to the Gelatine=—Those layers which yield the best and
most brilliant impressions, showing plenty of contrast, which have
been fully printed under a vigorous negative, most often exhibit a
disagreeable tendency to adhere to the paper in the high lights. The
greater the proportion of isinglass present in the film the more will
this fault manifest itself, particularly with an enamel paper. An
application of a diluted solution of ox-gall to the film, the use of a
thick well-sized or glazed paper, lighter pressure while printing, and
less frequent damping will all tend to diminish this evil. Layers of
this nature are extremely liable to damage, and the adhesive portions
will soon suffer unless the greatest care is exercised.
=Ink Remains upon the Plate.=—Through too light or uneven pressure it
sometimes happens, especially when using a stiff ink, that the latter
will, after the impression has been pulled, partially adhere to the
darkest portions of the printing surface, particularly on the edges
of plates deeply copied. If this fault is not corrected at once, and
the printing allowed to proceed, these portions giving a light, faulty
impression will gradually increase in size, and the corresponding
portions of the Collotype plate gradually darken. When first observed
the whole plate must at once be cleaned with turpentine and again
rolled up with thinner ink, a greater and perfectly even pressure being
applied. Small faults of this nature occurring on the edges of the
plate can be corrected after each faulty impression by means of a small
piece of sponge moistened with gum water or with a turpentine rag.
=Displacement of the Paper= under the scraper will create a double
impression, and sometimes wrinkles, the latter invariably leading to
the destruction of the plate. By adopting the use of the bridge now
used in conjunction with most Collotype hand presses, this fault is
avoided, as the paper is only in contact with the printing surface
immediately under the scraper.