AUTOGRAPHY.
There are several methods of transferring from specially prepared,
or even any strong well-sized paper.[O] As the latter may be most
convenient, proceed as follows: Write with autographic transfer ink,
readily procurable from dealers in litho requisites; this will keep
for years, and may be used with any clean steel pen. After the writing
has dried, damp the back of the paper with dilute nitric acid—1 to 3
of water. When the writing is visible through the back of the paper,
the sizing has been acted upon sufficiently; the sheet should be placed
in a porcelain dish, washed in several changes of water, and blotted
off, leaving it evenly damp without being exactly wet. In the meantime
a stone should be adjusted upon the bed of the press, rubbed over
with pumice powder, and warmed—this may be easily effected by pouring
spirits over the stone and igniting it. A suitable scraper—one which,
when pressed against the stone, allows no light to pass between, and
which should not be wider than the stone—is adjusted in the scraper
box. The screw or other appliance for regulating the pressure is then
adjusted. The transfer is carefully and accurately placed upon the warm
dry stone, with the writing or drawing face downwards in contact with
the polished surface, a few sheets of waste paper are placed over the
whole, the tympan (the upper surface of which has been freely rubbed
with tallow) is lowered into position, the bed is then pushed, with the
stone so covered, under the scraper box, so that the scraper may come
down, not upon the extreme edge of the stone, but about four or five
cm. from the end, lower the scraper (or, according to the construction
of the press, raise the bed) and pull through under gentle pressure.
Release the pressure of the scraper, withdraw the bed, and raising the
corners of the waste sheets used as backing paper, convince yourself
that the transfer is in a proper position and has not moved; replace
the covering paper, change the position of the stone so that it passes
under the scraper in a reversed position, pass through the press again,
this time with greater pressure. Repeat these operations three or four
times, on each occasion under steadily increasing pressure; remove the
transfer carefully by one corner, and allow the stone to become cold;
sponge over with thick gum solution, and in this condition it may be
left for any length of time. Great care must be taken that none of the
tallow used on the tympan, or other grease, comes in contact with the
stone, either by the hand, covering paper, or other means.
[O] Transfer paper is more reliable.
If the transfer should exhibit any signs of weakness while the stone
is still covered with plain gum water, take, upon a small linen pad, a
little ink thinned either with tallow or a few drops of turpentine; by
careful rubbing in different directions the lines will be considerably
strengthened. Plenty of gum must be kept upon the surface of the stone
during this operation, at the completion of which it may be removed
with a sponge and water, and the inking-up completed with the roller
and the stone gummed in.
Before printing, the gum has to be removed by water, and the stone
rolled up with a moderately stiff ink; it is then etched with gum water
rendered slightly acid by a few drops of nitric acid. The best test for
the acidity of this solution is to add just so much acid to the gum
water that, after its application to the edge of the stone for two or
three seconds, scarcely perceptible bubbles of carbonic acid gas will
show. This is applied evenly to the drawing with a sponge, and allowed
to act for a few seconds.
Should the ink “take” to the stone in places other than the design or
writing, rub the spot at once with woollen material moistened with gum
water; this will clear away the superfluous ink, but the part should
be carefully watched during the printing for any recurrence. After the
removal of each impression the stone is damped over the whole surface
with a damping cloth before another application of the inking roller.
For the production of perfect impressions avoid contact of the hands
with the face of the paper or stone, and care must be exercised
that all matters connected with the printing are kept scrupulously
clean, any contamination of a fatty or greasy nature especially being
strenuously avoided. The paper used in lithographic printing is usually
slightly damped by placing between sheets of damp blotting paper; such
proceeding is not absolutely necessary, as dry sized paper may also be
used.
The above detailed description of the necessary sequence of operations
in the Autographic transfer process will assist in understanding that
of photo-lithographic transfer, which requires still more care, and the
use of a special transfer paper so prepared that it is sensitive to
light.
THE BITUMEN METHOD.
This, the earliest photographic process, was discovered and described
by Niepee even before the discovery of photography or silvered plates.
It depends on the peculiar property asphalt possesses of losing its
solubility in ether, benzine, or turpentine after prolonged exposure
to light. If it be dissolved in turpentine in a photographically
dark room and the solution poured upon a well-polished metal plate
or lithographic stone, dried, and exposed under a reversed negative
(otherwise the impression yielded in printing will be reversed)
for two or three days[P] in sunlight, the picture may be developed
with turpentine or benzine, either of which solvents will remove
the layer from such portions as have been unexposed to the light
and reveal a picture in asphalt that may be rolled or inked-in and
capable of withstanding etching. This direct process, as applied to
photo-lithography, is now of little practical value owing to the
introduction and perfection of the transfer process. It is, however,
most valuable in heliographic engraving or etching and for the
production of zinc and copper printing plates.
[P] The bitumen most suitable is that variously known as Syrian
asphalt, Jew’s pitch and bitumen of Judea. This is finely
powdered and placed in a bottle with twice the bulk of ether
and occasionally agitated for five hours, at the end of
which time the ether may be poured off and fresh supplies
added so long as any portion soluble in the ether remains.
The purified residuum maybe dried and dissolved in benzole
or chloroform; this will yield a solution which may be
used as above, but poisoning, perhaps, twenty times its
sensitiveness. The picture is developed with turpentine.
DIRECT PHOTO-LITHOGRAPHY.
This method is little known, and it may be said that it has never been
developed to a practical issue. It is here only incidentally referred
to, but at the same time the fact may be pointed out that these two
direct photo-lithographic processes possess a value, inasmuch as they
may be utilised in a comparatively easy manner for the production of
grained or half-toned pictures, presenting less difficulties than by
the transfer process.
On to a well-cleaned stone, the surface of which may be either finely
grained or polished, a solution of gum arabic and bichromate is spread,
dried in the dark, and exposed for a sufficiently long time under a
negative; if the latter be a film it will facilitate the examination
from time to time of the progress of the copying. On completion of the
exposure the stone should be well washed with water and rolled in with
ink.
Morvan’s process is of a similar nature; a stone is coated with an
admixture of albumen 200 g., water 300 g., bichromate of potassium
50 g., dried and exposed under a stripped or paper negative. The stone
is then first washed with soap, and afterwards distilled water, and
then rolled up, gummed, and the ink allowed to set awhile, after
which printing may be at once commenced. In none of these methods
is mention made of etching the stone after inking-in, as is usual
in lithography; it may be here noted that photo transfers will not
withstand so vigorous an etching as drawings executed upon stone in the
usual manner. A photo-lithographic transfer may be quite ruined, even
entirely destroyed, by careless etching; this is therefore a point of
great moment, and one which has not usually been considered or dealt
with in published methods of procedure. We shall have occasion to again
refer to it.
PHOTO TRANSFER FROM PAPER.
In this method, now universally employed, success may be said to depend
more particularly upon two points. (1.) The paper for the transfer.
(2.) The suitability of the negative for the purpose in view. The
properties and preparation of a suitable transfer paper demand a few
words. It should be of substantial body, smooth and well sized; that
known as bank post is usually employed in this country. Professor
Husnik in his patented process proceeds as follows: 1 part of finest
gelatine is swelled, and then dissolved in 24 parts of water a solution
of chrome alum 1-100 in water is added, and the solution while still
warm is poured into a large zinc dish heated to 34° R. by means of
a petroleum or spirit lamp. Remove any scum from the surface of the
solution, float the paper one sheet at a time, and suspend to dry. The
sheet is floated upon the gelatine solution a second time, and once
more suspended, this time by the diagonal corner to that by which it
was previously hung. Prepare a solution of white of egg 1 part, water
2 parts, and on this float the paper on one side. After again drying
it is ready for sensitising, for which operation prepare a bath of
water 14 parts, bichromate of potassium 1 part, methylated spirits 4
parts, adding sufficient ammonia to turn the reddish solution a bright
yellow. If the paper is not prepared in large quantities, but only
for immediate use, the ordinary gelatine paper of commerce[Q] may be
employed with advantage, if further prepared by floating upon a bath
of albumen (beaten to a froth and allowed to stand) 50 parts, water
50 parts, bichromate of potassium or ammonium 7 parts (Märkl), upon
which bath the paper should be floated for five minutes. This solution
is subject to the disadvantage that even in the dark it will not keep
for more than a day or two, therefore it must be used at once. All
photo-lithographic transfer papers, after sensitising, should be used
within a few hours of their preparation or their good qualities are
partially sacrificed, the solubility of the albumen layer in cold water
being impaired. Photo-lithographic transfer paper prepared as above
described has been for some time in the market, and may be procured
as an article of commerce, in an unsensitised condition; it will keep
indefinitely in this state, and may be sensitised as required. The
surface should not be allowed to remain in contact with the bath,
neither should the immersion be lengthy, as in either case the surface
of the paper would probably suffer. After drying by suspending by one
corner in the dark, the chromated paper is exposed under a suitable
negative—if possible to the sun—for a few minutes only; it may be
examined by non-actinic light, and when the image appears brown or grey
upon a yellow ground, and all details are visible, it is removed from
the copying frame and entirely covered with a thin coating of transfer
ink. This as purchased is much too stiff for use, and must be reduced
by means of turpentine to such a consistency that it is possible to
distribute an even and quite thin layer upon the surface of the print,
without its penetrating to the paper. The ink should be so thin that it
presents a grey, not black, appearance.
[Q] For instance, the double transfer paper as used in the carbon
process.—TRANS.
Those who may find it necessary, or who care to prepare their own ink,
should take—chalk ink (printing) 4 parts, beeswax 10 parts, resin 7
parts, turpentine 40 parts, tallow 8 parts, Prussian blue 6 parts,
ground and mixed in a paste. The chalk printing ink should be melted
by gentle heat, then add the wax and resin in a molten condition, then
the tallow, and lastly the Prussian blue and turpentine; on account
of the inflammable nature of the latter these operations should not
be conducted at an open fire. If, after prolonged keeping, this ink
becomes tough, and does not readily leave the transfer paper when
transferring to stone, the addition of a few drops of olive oil will
restore it to a usable condition. The ink is best applied by means of
a fine, dry sponge,[R] with which it should be spread on the transfer
as evenly as possible, during which operation the print must be
protected from actinic light; on its completion the print is placed
aside to allow the turpentine to evaporate. This in a warm room will be
about ten to fifteen minutes; the print is then placed in cold water,
care being taken to remove any air-bubbles from its surface. After
remaining for about half an hour the uppermost layer will have become
sufficiently loose to allow of its removal, together with the adherent
ink not forming part of the picture, upon the application of slight
friction.
[R] A smooth composition roller answers equally well.—TRANS.
=The Development= is readily effected by means of a small, fine wet
sponge, or a pad of cotton wool well moistened, which is passed
over the print a few times with gentle pressure; it will be found
convenient during these operations to place the transfer face upwards
upon a sheet of glass.
Judgment may be formed at this stage as to the suitability of the
negative, and also as to the correctness or otherwise of the exposure
under it of the sensitised paper; if it should have been too short the
finest lines will not be firm, but appear broken or “rotten,” as it is
technically termed. On the contrary, should the exposure have been too
long, the spaces between the lines, which should be quite free from
ink, will retain a certain amount, in attempting to remove which the
transfer will be damaged.
=Washing.=—Exposure, inking, and development being satisfactory, the
print is thoroughly washed to remove the chrome salt. Dry the transfer
by means of repeated applications of blotting-paper, and it is then
ready for transferring.
=Transferring.=—The print should retain a little moisture, but be by
no means wet. It should adhere to the warmed stone to prevent any
probability of it moving while passing through the press.
=Transfer too Adhesive.=—Should the gelatine surface, in the judgment
of the operator, appear likely to prove too adhesive, it may be further
dried before use, or placed for two minutes in a one per cent. solution
of tannin, and again dried between blotting-paper.
=Preparation of Gelatine Transfer Paper=, as used in the Imperial
Military Geographical Institute in Vienna, is described as follows
in the “Photographic Correspondence”:—A sheet of well-sized paper
is soaked in a dish of water, and when thoroughly limp is allowed to
drain, and then placed on a horizontal glass plate. All air bubbles
and superfluous moisture are removed by blotting-paper and a squeegee,
the edges of the paper are turned up to the depth of about 2 cm., and
a warm gelatine solution (1 to 30) poured upon the paper. It sets in
a few minutes, and the sheets are placed upon wire gauze to dry, this
operation usually occupying about two days. A day before using the
gelatine paper is sensitised by immersing for three minutes in a cold
bath of bichromate of potassium (1 to 15). On removal from the bath it
is allowed to drain, and the gelatine side placed upon a glass plate.
The back is dried with blotting-paper, and all air bubbles removed.
These operations and the subsequent drying must be performed in a
non-actinic light. It may occur that after these operations the sheets
when dry adhere partially or wholly to the glass plate. To prevent such
an occurrence it is well to wax the plate, as in the carbon process,
or to apply to the surface a weak solution of ox-gall.[S] When dry the
sheets are cut to the required size and printed under the negative. On
removal from the printing frame they are placed in cold water until
quite limp, removed, placed face upwards upon a glass plate, and
surface dried with blotting-paper. Should the gelatine swell too much
the sheet is placed for two minutes in a chrome-alum solution (1 to
200) and again blotted. Ordinary transfer ink, thinned with turpentine,
is now thoroughly rolled up on the inking slab by means of a leather
roller (as previously described in the instructions under Collotype);
a fine velvet roller, lightly charged with ink, is then passed over
the still moist transfer. Should the latter become dry in places it is
again passed through the water bath, and the inking is again proceeded
with. If the ink adhere to other parts than the design it is easily
removed by the application of a damp sponge or the tip of the finger.
The process of transferring to stone is as previously described. The
stone itself is prepared in the manner described for the autographic
process (see page 135). Damp the back of the transfer with water only,
and after passing through the press several times, remove the paper
from the stone; if of good quality this may be done without tearing.
The transferred impression being still easily obliterated, it is better
to let the stone stand for a few hours without gumming; this will allow
the ink to dry deeper into it. Coat the whole of the surface with a
moderately thick solution of gum, and again allow to dry. In this
condition it may remain indefinitely, but under any circumstances it is
advisable to allow it to remain a day before etching and printing. The
gum solution used should be freshly prepared, as when old it becomes
acid and acts as a mild etching medium. Remove the gum with a clean
sponge previously to printing, and while the stone is evenly damp with
gum solution the picture may be either rolled up with stiff chalk ink,
applied by means of a leather roller, or, as preferred by many, rubbed
in with a sponge containing thinned transfer ink. When the drawing
appears clean and perfect the stone is washed with a wet sponge, coated
with gum, placed aside to dry, and allowed to stand for a day. After
the removal of the gum proceed as previously described, viz., roll up
with stiffish ink, nowhere allowing the stone to become dry, and etch.
This operation must be conducted with care and judgment, or there
will be a probability of losing the finer lines of the drawing. The
best mordant to use is nitric acid, so dilute as to taste no stronger
than lemon juice, and which, placed upon the edge of the stone for a
few seconds, will show only slight effervescence. To this is added a
little gum-water, and it is then evenly and quickly spread over the
stone. After being allowed to act a few seconds, the stone is sponged
over with clean water, and is then ready for printing from.[T] There
are many practical lithographers who prefer to entirely remove the
visible image from the stone by means of turpentine before printing. A
little gum is left upon the stone, and while the latter is still moist
the drawing is removed by means of turpentine upon a piece of rag;
the latter must not be too frequently changed, or a too liberal supply
of turpentine made use of, or the drawing may be irreparably damaged.
Unless the latter be the case the picture will reappear upon applying
the roller charged with chalk ink. As may be expected, the first few
impressions are seldom so perfect as the later productions. After each
impression is removed the stone is at once slightly moistened. For this
purpose a soft, clean sponge is suitable, or damping cloth, as supplied
by dealers in printing materials. The sponge or cloth should be
thoroughly wetted, wrung as dry as possible, and in that condition will
possess the necessary dampness. In rolling it should be borne in mind
that as in Collotype a stronger grip of the roller handles and heavy
pressure with slow rolling will deposit ink upon the drawing—while, on
the other hand, light quick rolling of the drawing will tend to remove
the ink. To leave the stone without gumming after transferring is a
convenient method of rendering the transfer more receptive of the ink.
In lithographic as compared with Collotype printing the ink is reduced
to a far greater extent with varnish, while both the inking slab and
roller are charged far more heavily. The paper may be damp, or a dry,
well-sized paper may be used.
[S] A more reliable method of imparting to the surface of the
paper a high gloss is to squeegee it down upon a ferrotype
plate, the surface of which requires no preparation, and the
risk of sticking is _nil_.—TRANS.
[T] For etching extremely delicate transfers a decoction of
Aleppo gall with gum is to be recommended. 15 gr. of crushed
nut galls are boiled for one hour in half a kilo of water
and strained through a cloth. To etch the transfer add a
few drops of this solution to a solution of gum of a syrupy
consistency; spread over the stone with a soft sponge, and
allow to dry.