Single Transfer Paper, which is paper with a thin coating of hard
gelatine. Now to proceed. Place a piece of single transfer paper
into a dish of cold water, and in three or four minutes the coated
side will feel slimy, then place in the same dish a piece of the
printed tissue face upwards. This will probably curl up at first and
afterwards flatten out again. When this has happened or in a few
minutes after immersion bring the piece of single transfer paper and
the print together, film to film, so that they may be in contact,
and square one with the other. Now holding them by one edge,
withdraw them together by sliding them out of the dish on to a sheet
of thick glass, a large cutting glass serves well, or stout sheet of
zinc.
This should be supported in readiness at the rim of the dish.
Having the transfer paper and print now on the glass or zinc, hold
them firmly and with a rubber squeegee press them closely into
contact, squeezing as much water out as possible.
A better way perhaps is, if the dish is large enough, to place the
glass or zinc under the two papers whilst in the water and so raise
them out.
The squeegeeing must be done thoroughly, firmly, and all
over--several strokes being given in each direction.
Next lift the papers, now in firm contact and sticking together, and
place them between blotting paper on which is a heavy weight. The
next print may now be proceeded with and so on.
The print should be between blotting paper and under pressure for
about twenty minutes, after which it is removed to a dish of hot
water--almost as hot as the hands can comfortably bear, say 100° to
120° F.
After lying in this for a few moments the dark pigment will be seen
to be oozing out from between the two papers. When this has begun to
come pretty freely take one corner of the print and pull it away
from the transfer paper. It should come quite easily, and on being
peeled off entirely it is thrown away. We have now the transfer
paper bearing the printed film reversed, that is, the side which was
previously at the bottom and next the original paper support, is now
uppermost and can therefore be got at.
If we splash it or lave it with the hand, using the hot water, we
shall soon see what happens. The smudgy mass of pigment begins to
wash away and the picture gradually appears.
This constitutes development and we continue working it with hot
water until the whole is clear and bright, being careful not to
touch the film with fingers or anything but water, for being in a
very delicate and soft condition it would be certain to sustain
injury.
The hotter the water the greater its washing-off action, and hence
in cases of over-exposure very hot water may go far to recover the
print. When the desired result is secured, transfer the print to a
dish of cold water, this instantly tends to slightly harden the film
by cooling it, and after two or three minutes it is passed into a
dish of alum and water, which further hardens it and also "clears"
the print of any bichromate salts which may still remain. In the
alum bath the print should remain until any sign of yellow stain has
disappeared, when after a final rinse of a few minutes in cold water
to remove the alum, the print may be hung up to dry.
It will be seen that there is no prolonged washing as with those
processes in which hypo is employed, and the print is absolutely
permanent.
It must be remembered, however, that in the finished picture we are
looking at the back of the printed film as it received the light
impressions from the negative, and hence the image is reversed, that
is, the left is on the right and the right on the left. For
landscape and views this reversed position will probably be of no
importance, but if it is desired to have things right way round--in
portraits it will be essential--we must either work from reversed
negatives, or we must again transfer the film which will then
constitute a _double_ transfer. We shall now understand why
previously we called the paper to which the film was transferred
_single_ transfer.
Inasmuch as it will be seen that the print is not on paper, but
consists of a transferable film of pigmented gelatine, it will be
understood that the paper employed is merely a support to that film,
hence it is customary to speak of the paper as the support, whilst
moreover it maybe, and as often as not is ivory, glass, textile
fabrics, wood, or other substances.
If now we wish to again transfer the film so as to correct the
lateral reversal, we substitute for the single transfer paper a
"_temporary_ support."
The temporary support which is to receive the film merely whilst it
is being developed, and with the intention of its being subsequently
transferred again to a _final_ support, may be paper or many other
things.
Moreover, remembering that the film is mainly gelatine, it should be
clear that whatever the nature of the surface of the temporary
support, the soft glutinous film will take that surface just as we
may make the impression of a seal in sealing-wax.
The normal carbon print is shiny, due to the gelatine, and so, if as
a temporary support we were to use ground glass or matt "opal," the
carbon print film would receive the fine granulated surface and give
a matted print as a result. This merely by the way as suggesting an
additional advantage offered by the double transfer process as a
set-off against the slight extra trouble.
If double transfer is determined upon, and it is not intended to
experiment with ground glass, etc., then when purchasing the carbon
tissue, some _temporary_ support (sheets of paper coated with
gelatine and shellac) should be procured, also some pieces of
_final_ support.
Whatever the temporary support, it must receive an application of
waxing solution. This also may be bought, or can be made of:--
Yellow resin 36 grains.
Yellow wax 12 "
Ether 2 ounces.
Melt the wax, add the resin, stir together and then add the ether.
Pour a little of this mixture on to the temporary support and spread
with a tuft of cotton wool, and rub over to make it even.
The final support for double transfer may be purchased, and is made
ready for use by soaking for ten minutes in alum.
The temporary support, after being waxed and the waxing solution
having become dry, is to take the place of the single transfer paper
in every respect, and the film developed as already described. When
it has reached the final washing, after the alum clearing bath, it
is brought into contact with the final support (which has been for
ten minutes in alum bath as just described) and is removed to the
glass or zinc plate and squeegeed.
It is now hung up to dry, and when quite dry the blade of a knife
should be inserted at one corner and the temporary support gently
pulled off.
Such is the carbon process, neither difficult nor lengthy, and with
this brief outline to form an introduction, the reader who is a tyro
will the better appreciate the fuller description which follows.
* * * * *
Whilst the article that follows is more comprehensive than the
beginner may require at first, he is nevertheless advised to read it
carefully through, and some points which may not seem clear at first
will explain themselves after a very little experience.
_The Carbon Process._
[Illustration]
Before proceeding to practical details of working, it may be as well
to realize what a piece of carbon tissue is, and what takes place in
the process of exposing such tissue to light. Mr. J. W. Swan, who is
to be regarded as the inventor of carbon process as we now know it,
was justified in giving the name "tissue" to the film of pigmented
bichromatized gelatine, as at first it was a tissue unsupported by
paper backing and containing pigment practically, if not entirely,
carbon. The terms "carbon" and "tissue" have been generally accepted
as describing a pigmented paper containing permanent colour,
therefore little if any misunderstanding is caused by such general
description. The carbon process, like other kindred methods, is
based upon the well-known hardening action of light upon a
bichromate salt in combination with organic matter. When paper is
coated with a mixture of gelatine pigment and a bichromate salt,
dried under favourable conditions and exposed to light under a
negative it naturally follows that a positive image is produced. The
negative acting as a screen, prevents any undue hardening of such
portions of the picture as are intended to form the high-lights,
only slightly interfering with what are to be the middle tints, and
practically permitting full play in the shadows. The latent image is
imprinted on and into the film of tissue compound with the most
delicate portions on the surface, and means must therefore be
adopted to protect the surface during the washing away of all parts
of the film not intended or desired to form any part of the finished
picture.[7] In Swan's process this object was secured by cementing
the surface of the printed tissue to its temporary support with
rubber solution, but after J. R. Johnson discovered that the printed
tissue would adhere without any cement to any surface impervious to
air and water simply by atmospheric pressure, the same end was
gained by soaking the undeveloped print in water until about _half
saturated_, then bringing it into contact _under water_ with either
its temporary or permanent support, slightly squeegeeing or sponging
to remove as much water as possible without injury to the print; as
to _air_, _there ought not to be any present_ if care is taken to
exclude it before lifting from the water bath. The half-soaked
tissue after mounting absorbs every particle of water from between
the surfaces, and thus secures optical contact.
[7] It is generally asserted by non-practical carbon printers
that all portions of the film behind that which finally forms
the print, are unacted upon by light. That is to say,
unchanged and quite as soluble as if not printed at all. The
upholders of such a theory should try the following
experiment:--Take a piece of tissue, cut it through the
centre, expose one piece, then mount both under precisely
similar conditions and wash in the same warm water bath.
Paying special attention to the backing papers, they will
find the one unacted upon by light will have parted with its
load of coloured material in much less time than the piece
that formed the backing of the print.
The squeegee, handy tool as it is, ought to be used with great care,
in no case with any degree of force, or serious injury will result,
particularly to the finer kinds of work, such as double transfer
prints of all kinds, either on paper, ivory or opal. The rubber edge
of the squeegee should be free from notches, often caused by contact
with the sharp edges of glass plates. The notches can be removed by
rubbing on a sheet of glass paper placed on a plane surface.
TISSUE MAKING.
The tissue compound consists of a mixture of the following
ingredients:--Gelatine, sugar, pigment and water. The proportions
are of infinite variety according to season, the nature of the
pigment used, and the purpose for which the tissue is intended. For
convenience it is the rule for tissue makers to prepare what is
termed stock jelly by dissolving, by the aid of a water bath,
gelatine and sugar in water, in varying proportions--roughly
speaking:--
Gelatine 2 parts.
Water 4 to 7 "
Sugar[8] 3/4 to 1-1/4 "
[8] For some purposes (instead of sugar), glycerine, sugar of
milk, or treacle may be substituted.
The pigments are made up into what are termed jelly colours, which
are ground either by hand on a slab of glass, marble or granite,
using a suitable muller for the purpose, or when large quantities
are required a paint mill driven by steam or other power is
employed. In hand grinding the colour is kept moist by syrup on
greatly reduced stock jelly. After grinding by hand the pigment is
lifted from the slab with a palette knife and stirred into melted
stock jelly. When the mill is used, the pigment is mixed with the
jelly before grinding. The proportion of pigment to jelly varies
enormously according to the nature of the pigment, and may be
anything between 2-1/2 per cent. and 25 per cent. Having prepared
stock jelly and jelly colours, and allowed both to set, they are
weighed out in proper proportions, the jelly being dissolved in a
tin vessel placed in a water bath. The colour, generally speaking,
is dissolved in a small proportion of the stock jelly placed in the
mill and again ground into the bulk of the jelly. In some cases the
pigment is dissolved in warm water and filtered through cotton wool,
fine felt or flannel. After adding powdered recrystallized
bichromate, the jelly compound is ready for coating or spreading on
the paper. The coating may be done by hand or machine. Several forms
of machine are in use, including the first form invented by Mr.
Swan. When only a small quantity is required, it is the general
practice to coat by hand.
In hand coating, the tissue compound may be strained through fine
muslin into a flat tin dish placed on a water bath; the surface
cleared of air bubbles by dragging over it a strip of stiff paper.
The sheet of paper to be coated is held in an upright position at
the further end of the dish with its bottom edge just touching the
surface of the solution, gently lowered until the whole surface of
the sheet is in contact with the solution. If the lowering is
properly done there will not be any default in contact, but if
allowed to rest on the solution a few moments, the presence of air
bubbles, if any, will be detected by the presence of little lumps on
the back of the paper, these may be removed by raising a corner
and touching the spots with a finger tip. The sheet is then raised
with a rather slow and steady motion, allowed to drip, then clipped
to a line by its top corners and left to dry in a warm dry room from
which white light has been excluded. When this method of coating is
adopted it is best to have the sheets of paper an inch longer than
the dish; the blank edge prevents contamination of the fingers and
distortion of the sheet caused by contraction in drying. Another
method of hand-coating is to roll the sheet into a tube shape,
placing the roll on the surface of the jelly compound one and a half
inches from the top of the free end, raising with rather slow and
steady motion as before. When the second method is chosen an oblong
and somewhat deep dish will be found better than the flat shape; the
flat dish may be used if tilted to give greater depth of solution in
a corner.
[Illustration: AT THE FOUNTAIN. J. W. WADE.]
In the manufacture of tissues the greatest care must be taken to
avoid over or long-continued heating of the gelatine solution.
Either a too high temperature or a lower temperature, long
continued, destroys the solution by rendering a considerable portion
of it soluble in cold water and to a great degree reducing its
gelatinous character.
The samples of gelatine used in tissue making are of two kinds,
although both of good quality they differ in solubility, in hot
weather a larger proportion of the "hard" sample is used, in cold
weather _vice versa_.
INSENSITIVE TISSUES.
All insensitive tissues are made with a single sample of hard
gelatine. They are stocked by dealers and must of necessity be fit
for use at any season of the year, to say nothing of those exported
to hot climates.
TRANSFER PAPERS.
Papers of many kinds are necessary for single transfer prints, the
tint of the paper must blend and harmonize with the tone of the
tissue or by contrasting help to produce a pleasing effect. For
prints of warm tones such as red chalk, terra cotta and the various
tints of sepia, a yellowish or cream-toned paper forms the most
harmonious basis; the various tints of black, blue, and purple look
best on a slightly bluish-tinted paper. For instance, a copy of an
old engraving in tissue, of the brown tone of the original would be
utterly spoilt by a blue-tinted basis. The above remarks apply only
in a limited degree to double transfer papers which in general use
are confined almost exclusively to portraiture. Such papers are
sometimes modified by tinting mauve, rose, opal, etc., etc. Such
tints are only in small demand and are in all cases confined to
papers coated with enamel preparations. The best and most durable
form of double transfer paper is that prepared on fine chemically
pure paper with colourless gelatine and made insoluble by the
smallest possible quantity of chrome alum, entirely without white or
tinted pigment of any kind. The best variety of double transfer
paper only differs from the finest form of single transfer paper in
having on its surface a rather thicker and softer coating of
colourless gelatine.
All transfer papers, either for single or double transfer, may be
coated in the same way as tissue, with the exception of those having
a very rough surface. All drawing papers and in fact all papers of
very rough surface are prepared by brushing over their surfaces
several coatings of a very thin solution of gelatine containing a
larger proportion of chrome alum or formalin than is used in making
ordinary single transfers. A flat camel-hair brush is best for this
form of coating, care must be taken to avoid air bubbles.
FLEXIBLE TEMPORARY SUPPORT.
Is paper coated with a gelatine solution in the first instance, and
after drying, again coated with an aqueous solution of shellac.
SENSITIZING THE TISSUE.
Pour the bichromate solution into a deep flat dish (porcelain,
ebonite, zinc, wood or tin) to the depth of half an inch to an inch;
place a sheet of tissue in it face upwards, remove air-bubbles with
a camel-hair brush or soft sponge, using as little pressure as may
be; turn the sheet and remove bubbles formed on the paper, turn the
sheet again face upwards, and passing brush or sponge gently over
the surface, keep it evenly wet until it is fairly limp; remove from
the solution, place face downwards on a perfectly clean glass or
zinc plate, squeegee to remove excess of solution, blot or wipe with
a soft cloth, remove any solution from the fingers, lift from the
plate, handle by edges only, clip to a line, small sizes by one
corner only, larger sheets by two corners, leaving a little
slackness between the two clips to allow for contraction in drying,
otherwise the sheet will be distorted and difficult to press into
contact with the negative.
The sensitizing _may_ be done in ordinary daylight. The drying
_must_ take place in a room from which actinic light is excluded,
and in a current of warm dry air, free from impurities, such as the
products of combustion from burning gas, or an escape of sewer gas,
etc., and at a temperature not higher than 120° F. The drying should
be done as quickly as possible, otherwise the tissue's keeping
property will be greatly reduced, and in all probability a thin film
formed on the surface, of insoluble gelatine, known to printers as
"decomposed tint," degrading the high-lights, and, except in the
case of very "hard" negatives, spoiling the work.
It will be evident to anyone that the fancy forms of sensitizing
have been carefully avoided--floating on the back, floating on the
face, etc., etc. All the results desired can be obtained by
immersion. If a hard negative has to be dealt with, a stronger
solution, or longer soaking in the bichromate solution, is all that
is needed; for weak negatives _vice versa_.
_Note._--In the dry frosty air of winter, sensitized tissue will dry
without heat, and continue soluble for a considerable length of
time, often as long as a month, or even longer.
In hot weather it is recommended that the solution of recrystallized
bichromate be made immediately before using, as in dissolving the
crystals a considerable reduction of temperature is produced. Should
the temperature then be over 60° F., ice must be used, not in the
solution, but roughly broken up and mixed with salt in an outer
vessel. If ice is placed in the bichromate bath allowance must be
made by keeping out part of the water. The ice should be encased in
several thicknesses of fine muslin to prevent the solid impurities
it generally contains getting into the solution. When recrystallized
bichromate is not procurable, a few drops of liquid ammonia added to
solution of crude bichromate is recommended. As bichromate is cheap,
a fresh solution should be made for each large batch of tissue.
PRINTING THE NEGATIVE.
Any negative that will yield a thoroughly good albumen print is
suitable for carbon work. The thinner negatives now made for P.O.P.
and similar processes are less satisfactory for direct prints in
carbon, for enlargements and reproductions such negatives can be
made to yield most satisfactory results by modifying the
transparency and the enlarged or reproduced negative. The latitude
in this direction is great. No matter how flat the original negative
may be, _if all the grades are present_ it can be manipulated in
such a way that the most brilliant result will be produced.
PREPARATION OF THE NEGATIVE FOR PRINTING.
The negative is prepared for printing as in all other processes by
removing all defects such as pinholes, streaks, etc. For the carbon
process the negative requires to be further provided with what is
termed a "_safe edge_;" this is a line of black varnish, from
one-eighth to half an inch in width according to the sizes of the
negatives, painted on its margin, either on the film or glass side.
In the case of original negatives masks of opaque paper are used
instead of the painted edge, the masks having openings cut in them
slightly less than the size of the negative. The purpose of the safe
edge is to secure a margin on which light has not acted, as such a
margin gives greater freedom to the operator in the process of
development by preventing the more deeply printed portions of the
picture leaving the support when the backing paper is removed.
DOUBLE TRANSFER PRINTING.
It may be explained in a few words why an ordinary (non-reversed)
negative must be printed by double transfer. In all other solar
processes when the print is removed from or taken off the face of
the negative, it is turned over to view, it therefore follows that
the details on the left side of the negative are found on the right
side of the positive print; with the carbon print no such turning
occurs, it is mounted upon its support in the same position as it
lay on the negative, developed in that position from the back and
leaving the position of objects the same as in the negative. In
some cases this reversal of the position of details is unimportant.
We will first consider the double transfer. In all double transfer
processes a temporary support must be provided. Such supports are of
two kinds, flexible and rigid. When a matt-surface print on paper is
required, finely grained opal glass is used. For the enamelled
surface patent plate, for intermediate or only slightly glazed
surface, a flexible support is used. Flexible support yields a
surface similar to an albumen print without special preparation.
When the higher glaze of the double-albumenized print is desired,
the printed tissue is coated with thin collodion before mounting on
the flexible support. Rigid supports, zinc or ground-glass plates,
have been used, but owing to the difficulty of seeing the details
during development their use is practically discontinued. Flexible
temporary support is always used in transferring to canvas, wood
panel, opal, ivory, etc., etc. In the case of canvas, the double
transfer process has two great advantages. First, staining is
avoided, the bichromate has been thoroughly got rid of in the
process of development. Secondly, the canvas is prepared to receive
the print by a substratum that allows the carbon image to expand and
contract with the expansion or contraction of the canvas and not in
opposition to it. There are also two advantages in adopting the
double transfer process for the production of pictures on ivory. The
first, is freedom from bichromate stains. Secondly, the ivory is not
distorted by washing in hot water, such distortion generally takes
place when the single transfer process is adopted. Wood panels are
prepared in a similar way to canvas. Stains are avoided, and as
there is not the expansion and contraction of canvas to provide
against, the substratum is modified in composition and greatly
reduced. The stains above alluded to are caused by the chemical
combination of bichromate with the lead of the paint, forming
chromate of lead or chrome yellow. In the case of opal, opaque
celluloid, and similar substances, no staining takes place, the
double transfer is only required to restore the image to its proper
position.
SINGLE TRANSFER.