Part 18

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._

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.

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.

The single transfer process is practically the only method in use when large sizes or large numbers of prints are required. For large sizes the negatives are reversed in the process of enlargement. For small sizes one or more reproduced reversed negatives are made, either in the camera from a carbon transparency, or by contact printing from a carbon transparency on a dry plate. With reasonable care, little if any loss of quality occurs in reproduction. As the single transfer process is the most simple form of carbon printing, it is generally recommended to beginners. Probably the most simple form of all is single transfer on opal. The opal plate does not require any preparation beyond cleaning. Neither soap nor grease of any kind must be permitted to contaminate the surface, otherwise the print will fail to adhere. Opal plates are cleaned by scrubbing with fine graining sand and water, and a muller or a small plate, either of ordinary or opal glass, placed upon the wetted sand and moved over the surface with a circular motion until soiled or discoloured markings are ground off.

THE ACTINOMETER.

An actinometer must be used to gauge the amount of exposure, as only a faint image, and in some tissues none at all, is visible during or after exposure. The simplest form of instrument is the best. That in general use is known as Johnson's Actinometer, a square tin box containing a long strip of sensitive albumen paper, and provided with a glass lid painted to the colour of printed albumen paper, an opening in the paint in the form of a slit three-sixteenths of an inch in width, from which the paint has been removed. The strip of sensitive paper is made to pass between the top of an inner lid and the painted side of the glass lid underneath the clear slit with the end of the strip protruding at one side of the box. On exposure to light the sensitive silver paper gradually discolours until it closely resembles the colour of the paint, that is called one tint; the tint is changed by pulling the slip forward just the width of the slit, and so on until the requisite number of tints have been printed for the strongest or densest negative in the batch exposed, those negatives requiring less exposure are turned down or removed when the requisite number of tints are registered in each case.

EXPOSURE.