The Barnet Book of Photography Part 26

Alcohol 4 "

DOUBLE TRANSFER TO OPAL AND IVORY.

After development the print is allowed to dry, and as soon after drying as possible it is transferred to its final support, whether opal or ivory, by a solution of gelatine composed of the following ingredients:--

Gelatine (fairly hard) 1-1/2 ozs.

Water 20 "

Chrome alum solution (30 grs.) 2 "

Soak the gelatine in the water until quite limp, dissolve by heat, then add the 30 grain chrome alum solution; roughly filter through two or more thicknesses of fine muslin into a flat dish on a water bath. After cutting the print to a size a trifle less than opal or ivory, place both print and final support in gelatine solution, allow print to stretch until quite flat, then bring them into contact under solution, squeegee and place on edge to dry. When quite dry, remove temporary support by inserting the point of a knife between the surfaces at the edge, wash with benzol or ether to remove all traces of the waxing solution. The print is now ready for the artist.

DOUBLE TRANSFER PRINTS ON CANVAS.

For double transfer prints on canvas, as a basis for oil painting, there is not at the present moment a large demand. A strong prejudice exists, and deservedly so, against such prints, for the following reasons. Some thirty years ago, in the princ.i.p.al establishment in which carbon work was done, a process of printing on canvas was in vogue. It was roughly this:--A stretched artist's canvas without other preparation was coated with dammar varnish; after drying, the canvas was used in pretty much the same way as single transfer paper is now--that is to say, a piece of printed tissue was squeegeed into contact with its surface, developed by floating on hot water, and practically in that crude condition placed in the hands of artists for oil-colour painting or finishing as it is sometimes prudently called. The natural result followed--_viz._, in a dry warm room the canvas stretched, the film of unmodified gelatine contracted; hence cracks, peeling, etc., until the work, valuable or otherwise, was utterly ruined. The method of preparing the canvas for the reception of the carbon image introduced by the writer is based upon opposite principles, as mentioned in the preceding general remarks, and may be described as follows:--A yielding and elastic substratum of gelatine forms a crust, so to speak, that expands and contracts according to the corresponding behaviour of the canvas support.

Ordinary painted canvas, such as is used by artists, or strong linen may be used with special treatment.

PREPARATION OF PAINTED CANVAS.

The canvas is first stretched tightly on a drawing board, same size as picture required, the greater part of paint removed by scrubbing with soda solution (either nail brush, sponge or a piece of flannel will answer the purpose) until the surface of the fabric is exposed and little of the paint remains beyond the priming. After drying, the canvas is coated with the following solution, applied with a flat camel-hair brush. Several coats (three in cold, four in warm weather) are given, drying between each and rubbing with fine sand paper if at all uneven.

Coating Solution.

Cooking gelatine (c.o.x's soup answers perfectly) 4 oz.

Sugar 2 "

Glycerine 2 "

Water 30 "

30 grain chrome alum solution 1 "

The print is exposed in the ordinary manner, developed on temporary support, allowed to dry and transferred to the canvas as follows:--The canvas is placed face upwards, on a level surface by preference, on a broad board over a large tank. The dry print is placed face upwards in a flat dish, the warm coating solution poured over it, air bells removed with the brush, the surface of the canvas brushed over with the solution. The bulk of the solution is then poured on the canvas and before it has had time to run off the print is lowered carefully and quickly upon it and squeegeed to remove excess of solution. After thorough drying, the temporary support is removed, the surface of the print cleaned with benzol or ether or a mixture of both to remove every trace of the waxing compound, and mounted on a stretcher in the usual manner. A print on canvas prepared as above, is perfectly reliable, it will neither crack nor peel, and can be used with perfect confidence as a basis for the most costly form of artistic finishing, as the carbon image rests upon an elastic substratum in actual contact with the fibrous substance of the canvas.

TO PREPARE ORDINARY STRONG LINEN OR CALICO.

Proceed precisely as for painted canvas (of course without scrubbing), using the same coating solution with half-a-pound white pigment added, sulphate of baryta answers perfectly. Sand or gla.s.s paper must be used pretty freely as the surface of the unpainted fabric washes up roughly when the gelatine coatings are applied.

WOOD PANELS.

Wood panels are prepared by removing the surface of the paint only with soda solution. After drying, a tooth is given by rubbing with fine sand paper and coating with solution as under:--

Gelatine (c.o.x's soup) 3 oz.

Sugar 1 "

Glycerine 1/2 "

Water 30 "

30 grain chrome alum solution 3/4 "

_Note._--Before transferring to either kinds of canvas or wood panel in cold weather, it is absolutely necessary to thoroughly warm the final support, otherwise the gelatine solution will gelatinize before the excess can be removed from between the surfaces.

THE SINGLE TRANSFER PROCESS.

The single transfer process may be briefly described as follows:--The sensitive tissue is exposed under a negative and the exposure gauged by actinometer as for double transfer printing.

After removal from the pressure frame the printed tissue is plunged into clean cold water along with a piece of transfer paper of any desired surface or quality, cut a little larger than the tissue (to provide a margin by which the picture may be handled without injury during development). After soaking the requisite time, the two prepared surfaces are brought into contact under the water, removed to a squeegeeing board, plate of gla.s.s or zinc, and squeegeed into contact; care must be taken to use only as much pressure as is needed to remove the superfluous water from between the surfaces. A sponge may be used instead of a squeegee, or both may be dispensed with, if care is taken to remove every trace of air from surfaces before lifting from the cold water bath. When neither squeegee or subst.i.tute for it is used, the print must be handled with greater care, as undue bending before atmospheric pressure comes into operation would destroy contact. The print is hung up to drain, and more time allowed between mounting and development. Development is the same as in double transfer, with one or two rather important exceptions. 1st. The single transfer print is developed upon the material on which it is to remain. 2nd. There is no preparation of the supports, neither in the case of paper or opal. 3rd. The developed print can be soaked for a considerable time in a saturated solution of alum without injury, the alum solution greatly a.s.sisting in removing bichromate.

CARBON TRANSPARENCIES.

Carbon transparencies, either for projection, enlargement, or reproduction, are printed in a special tissue known as transparency tissue, and developed on gla.s.s plates prepared with a thin coating of fine hard gelatine. The coating solution is composed as follows:--

Gelatine 3/4 oz.

Water 40 "

Bichromate potash 1 dram.

The gla.s.s plates are carefully selected, free from bells, scratches, and other defects; thoroughly cleaned, either by acid or rubbing with plate powder to remove every trace of grease, and then coated with the gelatine solution, and placed in a rack to dry; when dry, exposed to light to render the film somewhat insoluble. It is not desirable to print until the film is absolutely hardened throughout.

The print adheres firmly to the plate when the substratum is not over-printed.

A positive intended for projection should show clear gla.s.s in the highest lights without undue density in the shadows, all details plainly seen--in a word, quite transparent.

Positives intended for enlargement must be fully exposed--that is to say, every detail on the highest lights brought out, but no more; beyond that point there is nothing to be gained. Over-printing in the transparency tends to bury detail in the shadows of the enlarged negative, and to blend the highest grades in the high-lights, reducing the roundness or modelling of the picture.

In the case of very hard negatives intended for enlargement, the usual treatment is to sun the whole surface of the transparency in order to secure detail in the high-lights. A moment's consideration will convince any practical printer that nothing but injury to the final print can result from such treatment of the transparency. The high-lights are degraded, the details in the shadows further buried.

The better method is to make an extra special transparency tissue, for the printing of such hard negatives, containing a greatly reduced proportion of pigment to gelatine. Such a tissue permits greater depth of printing, retains all details in the shadows and high-lights, and, in fact, enables the enlarger to produce a negative that will yield a thoroughly satisfactory print.

REPRODUCED NEGATIVES.

In making reproduced negatives from hard originals, ordinary transparency tissue will serve every purpose. The transparency is printed in the usual way, and developed on a prepared gla.s.s plate; when dry a negative is printed from the transparency without special treatment and also developed on gla.s.s, when a decided reduction of density will be found to have taken place. The reproduced negative will possess all the good qualities of the original, plus improved printing quality. It is only in the case of extremely hard negatives that the extra special tissue is required.

If a perfect reproduction of an original negative is required, the transparency must be printed either in very weak light or in direct sunlight. Either method gives a brighter image than that produced in ordinary diffused daylight. The same method must be adopted in printing the negative.

_Note._--Care must be taken when direct sunlight is used to see that the pressure frame and everything in and about it is thoroughly dry, otherwise the tissue may stick to the negative, spoiling the print and probably the negative also. It must also be noted that two tints, printed in direct sunlight, although of apparently the same depth, mean quite as much as three such tints printed in diffused light.

FAILURES AND DEFECTS: THEIR CAUSES AND CURE.

As a rule, failures in working the carbon process are caused, as in most other cases of failure, by imperfect _knowledge of the substances and nature of the ingredients used in the process_.

Before going into further detail, it may be as well to point out that a great deal of misunderstanding has been caused, by writers on this subject--that may be fairly termed "blind leaders of the blind." With only slight knowledge of the subject they have misled beginners by a.s.suring them that the process is simplicity itself, in fact the most simple photographic printing process extant. Up to a certain point, and to that certain point only, is such description true. There are no subtle chemical combinations, no mixing and maturing of toning or other solutions. But--and in this case there is great virtue in the _but_--the greatest care is not only required, it is absolutely demanded, in manipulation. A carbon print from start to finish is probably subject to more chances of injury than any other form of print in existence. When this fact has been fully grasped by the novice, and he has been thoroughly prepared for the difficulties before him, the rest is plain sailing. Care, and care only; nothing beyond. He who wishes to succeed in carbon work must pay infinite attention to every small matter of detail as far as such detail relates to manipulation, otherwise he will only succeed in achieving failure.

FRILLING AND RETICULATIONS.

Frilly reticulations are generally caused by over-soaking the tissue before development, or failing to provide protection of the clear portions of the margin of the negative by a safe edge.

SPOTS ON THE FINISHED PRINT.