Photographic Reproduction Processes Part 11

Gelatine 35 parts Acetic acid, No. 8 250 parts Alcohol, 95 deg 50 parts Water 700 parts Chrome alum, 4:100 60 parts

Dissolve the gelatine in the acid at a moderate heat, add afterwards the alcohol and water, and lastly mix the chrome alum by small quant.i.ties at a time.

These substrata are employed to avoid the peeling off of the image. To prevent the entire desiccation of the gelatine, which is the cause of the defect above alluded to, it is advisable to add glycerine to the was.h.i.+ng water after the image is cleared. Some operators recommend a coating of flexible collodion, that is, prepared with castor oil, for the purpose in question. We do not think that necessary when the transparencies are not exposed to suns.h.i.+ne. If anything should be applied we would prefer the encaustic.

Carbon transparencies are invaluable for reproducing negatives in the original size by the same (carbon) process, or for enlarging by the collodion or gelatine process. For these purposes they should be made on the special red tissue manufactured by the Autotype Company, of London, Eng. They can, however, be made on the ordinary tissues.

Whatever be the tissue employed, the transparencies for the reproduction of negatives are seldom opaque enough, and should be intensified. This is done by treating them with a very dilute solution of sodium permanganate, which colors them olive green.

Transparencies for lantern slides, etc., are best colored with the couleurs a l'alb.u.mine of L. Encausse, sold by J. Reygondaud, Paris (France). They are transparent.(33)

_Toning and Intensifying.-_The carbon proofs can be toned and at the same time intensified by reagents acting with chromic oxide.

The dyes or coloring matters precipitated are not opaque, and, as a consequence, not objectionable for transparencies. The following processes are the most employed:

Prepare three solutions as follows:

A. Ferric sulphate 5 parts Water 100 parts B. Sodium carbonate 2 parts Water 100 parts C. Gallic acid 5 parts Water 100 parts

Dissolve the gallic acid in warm water. Filter each solution. They keep well.

To tone, the plate is immersed for, say, ten minutes in A, then, after rinsing slightly, it is placed in B for the same period, rinsed again and flowed with C until the desired color is obtained. The tone is a splendid purple black color. If a solution of pyrogallol be subst.i.tuted to that of gallic acid, the tone is green, and to a green bordering to black when a solution of catechu is used, the catechu exerting at the same time a tanning action on the gelatine. After toning, the plate should be thoroughly washed.

A similar process consists to wet the plate under the tap, then to flow over a mixture by about equal volumes of

A. Ferrous sulphate 5 parts Acetic acid, No. 8 5 parts Water 100 parts, filter B. Gallic acid 5 parts Water 100 parts

When toned, the plate is well washed, then flowed once with the alum solution and again washed. The tone by this process easily turns to an inky blue not very agreeable. The action should be stopped a little before the desired color is obtained.

It sometimes happens that the image in drying intensifies more then necessary. It can be cleared with a solution of oxalic or citric acid.

A brown sepia is obtained by toning first with pota.s.sium permanganate, 1 per cent. of water, then, after was.h.i.+ng, with a solution of pyrogallol.

If gallic acid be used instead of pyrogallol, the tone is black. By this process a great intensity is obtained. A dilute solution of ammonium sulphide can be employed as a clearing agent.

Pyrogallol and silver nitrate give a warm black tone.

Pota.s.sium b.i.+.c.hromate followed by silver nitrate form a brick-red precipitate of some opacity.(34)

Chloride of nickel and pota.s.sium ferrocyanate produce a fine brown.

Lime water and alizarine dissolved in alcohol dye violet.

Alizarine and the caustic alkalies produce a variety of tints, from violet to purple, according to the concentration of the solutions.

Lead acetate and alizarine in ammoniacal solution dye purple.

Pota.s.sium ferrocyanide and uranium nitrate produce a warm sepia tone. With chloride of nickel the tone is brown.

Ammoniacal solution of coralline diluted with water gives carmine red.

Pota.s.sium b.i.+.c.hromate and extract of indigo produce a fine greenish tone suitable for landscapes.

Extract of indigo colors blue(35)

Some of these reactions can be applied to the printing processes with the b.i.+.c.hromates, etc. The paper should be coated with galatine. See the Appendix.

Other colorations can be obtained with dyes in utilizing (as shown by Persoz) chromous chromic oxide as a mordant: alizarine, Brazil and yellow wood (morus tinctoria), Fustet (rhus cotinus), etc. The extent of this work does not admit of describing the numerous processes which can be employed; they will suggest themselves to the chemist.

The alkalies employed with the dyes should be employed in diluted solutions, as being liable to produce reticulation. By applying the coloring matters and the mordants thickened with a little starch, the image can be colored with different colors. Lantern slides can be thus colored with great ease.

PREPARATION OF RED, YELLOW, OR BLUE TISSUES.

_Red Tissue.-_Dissolve 10 grams of carmine in 1 liter of aqueous ammonia and evaporate. When the smell of the alkali has almost disappeared, add 1 liter of rain water. Of this take 65 cubic centimeters, add 35 c.c.m. of rain water, and in the solution let soak for an hour 15 grams of very soluble gelatine, add 1 gram of sugar, and dissolve in a water bath.

Filter, and take of the mixture a sufficient quant.i.ty (25 c.c.m. for a surface 1824 centimeters) to cover a sheet of paper which has been previously applied upon a gla.s.s plate in the following manner: In a tray full of hot water, immerse the plate and the paper; remove the whole in such a manner as the paper remains in contact with the plate; rub out the excess of water with a squeegee, and flow the gelatine over the paper still damp. Let cool on a leveled stand, and when the gelatine is solidified to a consistent jelly, remove the paper from the plate and place it to dry in an oven heated at not over 24 or 25 deg. C.

It is desirable that in drying the paper does not curl up. To that end, apply over it, before it being removed from the plate a wooden frame to which the gelatine, still sticky, will sufficiently adhere to hold the tissue when it stretches in drying.

_Yellow Tissue.-_Pulverize to an impalpable powder 25 grams of light chrome yellow in tablets (water color), and gradually add in stirring 1 liter of rain water. Take 100 c.c.m. of this and into it let soak for an hour 15 grams of the same gelatine used for the red tissue, add 1 gram of sugar, then proceed as above.

_Blue Tissue.-_In a liquid consisting of 85 c.c.m. of rain water and from 12 to 15 c.c.m. of blue ink, such as sold by stationers, let soak for an hour 15 grams of the same gelatine and 1 gram of sugar, and proceed.

_Preparation of Transfer Paper.-_Two kinds of transfer paper are employed-the enamel and plain transfer paper.

To enamel the paper: Dissolve 100 parts of barium nitrate in 500 parts of water, and, on the other hand, 200 parts of sodium sulphate in the same quant.i.ty of water. Mix, wash well the precipitate-barium sulphate-by decantation, and when well drained, mix to the following solution:

Gelatine, Coignet's 300 parts Glycerine 80 parts Ultramarine blue 1 part Crimson lake 0.1 part Water 2,500 parts

Let soak the gelatine for, say, one hour, dissolve by heat, then add by small quant.i.ties, stirring violently, 4 parts of chrome alum dissolved in 250 parts of hot water. Filter through flannel and coat the paper as directed to prepare the tissue. The mixture should be employed immediately after adding the chrome alum.

The plain transfer paper is prepared in the same manner, leaving out the barium sulphate and the coloring matters.

_Preparation of the Silver Paper.-_Immerse the paper for two minutes in a solution of-

Sodium chloride (common 2 parts salt, dry) Lemon juice 1 part Water 100 parts (filter)

When dry and wanted for use, sensitize the salted paper by floating for one minute on-

Silver nitrate 8 parts Nitric acid 0.1 part Water 100 parts

On its removal from the silver bath, sponge the paper between sheets of blotting paper and hang it up to dry.

ENCAUSTIC FOR SINGLE TRANSFER PROOFS.

White wax 25 parts Mastic 3 parts Turpentine 100 parts

Dissolve by heat, first the mastic, then the wax, and keep for use in a large mouthed vial.