FINISHING AND VARNISHING COLLOTYPE PRINTS.
=Retouching Prints.=—Under the above heading Leon Vidal, in his work
“Traité Pratique le Phototypie,” gives the following directions, which
I reproduce from the “Photographic Archives.” Even with the utmost
possible care in the preparation of the printing surfaces there will
be required in most impressions a little retouching, if only to hide a
few white spots. In large orders this cannot be carried to the extent
it is in silver prints. It happens in printing that particles of dust
find their way to the plate, and cause either light or dark spots in
the impressions; the former are covered by touching with ink, the
latter are removed with the erasing knife, and the white spot resulting
from the operation is toned down with ink. This spotting is quickly
performed. The paper being dull a colour should be used containing only
a small proportion of gum; it will then be invisible. Prints which
it is intended to varnish should not be spotted until they have been
sized, unless printed upon a paper already impervious to the varnish.
The colour most suitable of all is the actual printing ink thinned
with turpentine, by using which the trouble is avoided of mixing any
special colour to match the tone of the impression, as the two colours
are necessarily identical. Another advantage gained by adopting this
method is that the spotting may be completed before sizing, as the
aqueous solution of gelatine will not cause it to run. For impressions
in pure black the lithographic chalk is probably the best medium for
correcting proofs, as the colouring matter will be found to well
harmonise with the general appearance of the picture. A blacklead
pencil, on the other hand, is quite unsuited for the purpose on account
of the highly metallic appearance visible wherever the pencil has been
applied to the print. Retouching or spotting should not extend beyond
the removal of light and dark spots; the correction of larger faults
should not be entertained, but a fresh printing surface produced.
Faults present in the original negative should be carefully retouched
and removed or reduced as far as possible. Should the white margins of
the picture become soiled by contact with the inky mask or by finger
marks, they may be cleaned with indiarubber ink eraser. The backs of
impressions may also be cleaned in the same manner.
When copies have to be mounted on cardboard they may be either left
with a matt surface or varnished. In the first case, the edges are
trimmed, and they are then mounted upon the cardboard mounts. If the
latter have been previously damped they will retain their flatness.
=Rolling or Burnishing= must not be done until the prints have
completely dried, or the picture may be torn from the mount.
=Sizing and Varnishing.=—Prints to be varnished may be printed on
prepared or sized paper, and in such cases may be at once varnished.
If, on the contrary, the paper is not sized, they require a special
preparation, as follows:—A 10 per cent. solution of gelatine is laid on
with a broad camel-hair brush, avoiding air bubbles and streaks. After
a little practice this operation will be found both easy and rapid. The
sized pictures are pinned in pairs back to back on a wooden frame, to
which strips of cork are attached; when the prints are quite dry the
operation of varnishing may be proceeded with. A good varnish, probably
the best for the purpose, which possesses the double advantage of
remaining colourless and setting very hard, consists of a solution of
15 parts of white (bleached) lac in 100 parts of wood spirit (vegetable
or wood naphtha). On dissolving the shellac it will be found that the
solution is clouded on account of the suspended fatty matter, the
removal of which is always desirable; the varnish will then filter more
rapidly and give a more glossy coating. By adding powdered lime three
parts of the solution may be decanted clear, and the remainder may also
be used after filtration through felt. Or if to three parts of varnish
one part of benzine or petroleum ether be added, the solution will
resolve itself into two layers, and the upper one, which will contain
the fatty matter, may be poured off. The varnish is best applied by
means of a ball or dabber, care being exercised to avoid air bubbles;
the print is next placed in
=The Drying-box= (see fig. 8), which is a four-sided tin box 1 m. long
by 0·25 m. high. A gas-pipe, perforated with small holes drilled about
6 to 8 cm. apart, runs through the upper part of the box, the front of
which is open to two-thirds its height. A plate, finely perforated,
divides the upper third from the lower two-thirds, and forms an inner
division, through the upper of which the gas-pipe passes. The flat
perforated division is hinged to allow of being opened for the purpose
of igniting the gas. The pictures placed on the bottom of the box dry
very rapidly, while the perforated division prevents the possibility
of the ignition of the vapour of the spirit employed. With such an
apparatus it is possible to varnish and dry a large number of prints in
a very short time.
[Illustration: _Fig. 8._]
=Sizing may be Avoided= if each picture, after well drying, be dipped
into the following solution: Water 500 g., borax 130 g., white shellac
100 g., carbonate of soda 6g. The borax and carbonate of soda are
dissolved in boiling water, and the powdered shellac then added in
small quantities; when solution is complete carefully filter and allow
to cool. The impressions, two and two, back to back, are pinned on
frames, dipped in the varnish, and afterwards dried. By this procedure
a shellac coating is given to the surface only of the print; there is
no gelatine substratum to soften through atmospheric influences, and so
crack and destroy the layer of varnish. In winter the temperature must
be kept high, and the solution should be heated 15° to 20° C.
=Parchmentising= to a slight degree may also be adopted to close the
pores of the paper. Add one part by volume of water to two parts of
sulphuric acid, allow it to become quite cold, immerse the pictures for
one second only, and at once wash in a copious supply of clean water
to which has been added a small quantity of ammonia to effectually
neutralise the acid. The action of the acid must not be carried too
far, as it is merely necessary to act on the surface. To prevent paper
so treated from cockling while drying, it must be put under pressure or
stretched upon a frame; when quite dry it has to be varnished and dried
by heat.
=Varnishing Enamel Paper= without previous sizing is best done by means
of an alkaline solution of shellac prepared as follows: Place in a six
litre tin flask 1/2 kilo of bleached and powdered shellac, pour over
it 1-1/2 kilo of alcohol and 1-1/4 kilo of strongest ammonia. In the
course of a few days the solution of the shellac will be complete,
then add, with constant stirring, 2-1/2 kilo of hot water, and when
cold filter. It may be applied to the print with a broad Blanchard
brush,[K] and left to dry in a horizontal position. The prints may also
be floated on the varnish for about half a minute, and then suspended
to dry by means of clips. After a few minutes have elapsed a piece
of blotting paper should be applied to the bottom edge to absorb the
superfluous varnish.
[K] Made as follows: Take a piece of glass, say 20 cm. long by
6 or 7 cm. wide, and a piece of swansdown calico the same
width as the glass but only 6 cm. long, fold this over the
one end of the glass, 3 cm. being on each side, and bind
round with thread or spring on a rubber band.
=Rolling or Burnishing= must on no account be attempted until the
mounted prints are perfectly dry, otherwise they may be seriously
damaged or even completely torn from the mounts.