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.

For double transfer from opal the materials required are opal plates, sensitive tissue, French chalk, collodion, double transfer paper, pressure frame, flat camel-hair brush, chamois leather.

Before placing the negative in pressure frame, carefully clean from both sides all finger marks, etc., with the leather, place negative in frame on a paper mask, or provided with a safe edge. After exposure to light, remove from frame and develop on plate prepared as follows:--Rub the whole surface with French chalk on a pad of muslin, afterwards removing loose particles by gentle brushing. Coat with collodion made as follows:--Enamel collodion, 1 part; ether, 1 part; alcohol, 1 part. Filter and coat by pouring a pool on centre of the plate, and, by tilting it, force the collodion to flow into the top right corner, then to the left, then to bottom left, and finally drain off at bottom right corner, rocking the plate the while. The collodion must be allowed to set until it will bear the gentle pressure of a finger in its thickest part, but must not be permitted to dry in any part before plunging into clean cold water to remove the solvents by washing. The time required in washing is variable according to time of year. When the collodion ceases to repel water it is ready to receive the printed tissue. Soak the tissue for the requisite time, but not so long as to become quite saturated, bring it into contact with collodionized side of plate, remove to squeegeeing board, place over it a piece of wet rubber cloth, or a piece of wet thick single transfer paper, coated side up, to prevent injury to exposed margin of collodion and to facilitate the smooth passage of squeegee over the surface in removing excess of water. If, on removing the covering from the plate, the back of tissue is found to be unevenly wet, blot or place plate in a rack to drain; in a few minutes develop in warm water, temperature 90 to 100 F. Be careful to remove the backing paper _under water_, _and as soon as possible after immersion_ in the warm bath. Finish development by laving or pouring warm water over the print from jug or other vessel, until all details are brought out.

When washing is finished the print should look rather light, as in drying a decided increase in strength is obtained; rinse _slightly_ in alum solution to stop bleeding only, place in clean cold water to wash out any remains of bichromate, thoroughly rinse by dashing water upon the print to remove any particles of solid matter that may have stuck to its surface; place in a rack to dry, and transfer as soon after drying as possible. The transfer paper is cut a trifle larger than the net size of the print, but less than the opal support; it is soaked in warm water until the surface is slimy to the touch, but not soft enough to break under pressure between finger and thumb. The softened transfer paper is placed in clean cold water into which the dry print is plunged, water dashed upon its surface to remove air; the two surfaces are brought into contact under water, and squeegeed into contact as in first mounting before development. When thoroughly dry, the print may be removed from the opal plate by inserting the point of a knife at the edge.

Double transfer prints with enamelled surface are produced precisely as above, only substituting patent plate for ground opal, and by adding a second thickness of paper to the back of the finished print before removal from its temporary support.

DOUBLE TRANSFER FROM FLEXIBLE SUPPORT.

The flexible temporary support is prepared by waxing. The waxing solutions are:--

No. 1.

Benzol 1 oz.

Pure beeswax (natural not bleached) 3 grs.

No. 2.

Turpentine 1 oz.

Yellow resin 10 grs.

After dissolving, mix the two solutions, pour a little of the mixture on fine flannel, rub it over so as to evenly moisten the surface of the flexible support, wipe off with a second flannel using only slight pressure but rubbing briskly and with circular _motion_. When finished, the waxed surface should be perfectly even and quite free from streaks or other markings. The waxing should be done some considerable time before the support is required for use, and exposed to the free action of air to remove all trace of the solvents.

PAPER PRINTS WITH ORDINARY OR SLIGHTLY GLAZED SURFACE.

After removal from the pressure frame, the tissue is plunged into cold water with a piece of support slightly larger. After soaking the necessary time, the prepared surfaces are brought into contact under water, removed from the bath and placed upon any even plane surface, such as zinc, glass, etc., squeegeed into contact, blotted or otherwise treated to remove uneven dampness, and developed in warm water as in double transfer from rigid support, then slightly rinsed in alum solution and washed in clean cold water until all traces of bichromate are removed. After the transferring is done as before described, only the print on flexible support must be soaked in water until quite flat before bringing into contact with its final support.

PAPER PRINTS WITH HIGHLY GLAZED SURFACE.

The printed tissue after removal from the pressure frame is coated with collodion, for this coating allowance must be made in printing.

A considerable reduction in temperature takes place and any moisture present in the air is condensed on the tissue, bringing into action the well-known effect of continued moisture, _i.e._, considerably increasing the depth of the print. Great care must be taken to coat evenly and to prevent the collodion running in streaks on the back of the print. When such streaks or unevenness of any kind are present, a corresponding dark line or lines will be found on the face of the finished print. Transfer same as for prints with ordinary surface. All prints from flexible support on paper with a highly glazed surface as well as those intended for transfer to ivory or opal are coated with thin collodion:--

Enamel collodion 2 parts Ether 4 "