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Color Photography - Duxochrome And Colrstil Color Printing Films

( Originally Published 1938 )



FOR PRINTS OR TRANSPARENCIES

DUXOCHROME is a process similar to the Wash-Off Relief, except that it contains, in addition to the silver emulsion, the complementary colors embedded in the gelatin so that when you have exposed, developed, fixed, washed out and bleached, you have at once a colored positive in standard colors, without the necessity of dyeing the relief yourself. Duxochrome is made in two types, one which is firmly attached to the celluloid base and is eventually bound up as a transparency and one which allows the stripping or successive transfer in registration of the colored gelatin images to paper. The latter or stripping type must be stored in a humid place to keep the gelatin emulsion coating from separating from the celluloid backing before use.

INSTRUCTIONS FOR ITS UsE.--Exposure must in all cases take place through the celluloid side with a safe edge mask. Even though the negatives are in perfect balance, different times must be given to the different color sheets, since the dyes incorporated in the emulsion change the printing time. AlSo the silver emulsion on different colors is different. Small pieces are en-closed in the package, and the exposure time may be found by trial with these before using the larger sheets. As a rough guide, five to fifteen seconds (de-pending on the density of the negative) will be about right for contact printing, with the negative three feet from a 4o-watt electric lamp.

DEVELOPMENT.—The three films may be developed together in a sufficiently large dish. Under no conditions may developer be used a second time. Development of the Duxochrome films depends upon the strength of the developer, its temperature, and upon the three negatives. The following solution represents normal strength:

Duxochrome developer, solution A 340 min. 20 ccm
Duxochrome developer, solution B 340 min. 20 ccm
Distilled water 7 OZ. 200 ccm

Develop for four to five minutes at 65° F. (18° C.). Hard negatives require shorter development, increasing the temperature of the developer.

When printing from very thin negatives, increase the quantities of the solutions up to the following:

Duxochrome developer A 510 min. 30 ccm
Duxochrome developer 510 min. 30 ccm
Distilled water 7 OZ. 200 ccm

Time of development must then be increased up to six minutes, temperature being about 65° F. (18° C.).

It is absolutely necessary to use distilled water. The foregoing quantity of solution will develop three films together of 3% by 4 1/4 or 4 by 5 size. For small pieces, the following quantities may be useful: Solution A, 70 min. (5 ccm) ; Solution B, 70 min. (5 ccm) ; Water 13/2 oz. (46 ccm).

No importance should be attached to the appearance of the image. This commences to build up from the celluloid side (through which it was exposed) and only a faint image may be seen on red and yellow films, while it will be almost invisible on the blue. This, however, is quite in order, and the positive in its final form will not be seen until after the hot-water bath, to be described later.

During development, the three films should not be allowed to lie together at the bottom of the dish. After placing them singly in the solution and ensuring that they are properly covered, the bottom film should be withdrawn and replaced on the top. The dish may be rocked for a few seconds, and then the film now at the bottom should be similarly dealt with. By proceeding thus throughout the whole time of development, the films will be evenly developed and a patchy appearance avoided.

Without rinsing in water, the films, after development, are transferred to an acid fixing bath containing only hypo and potassium metabisulphite:

Hypo 4 oz. 115 g
Potassium metabisulphite 200 gr. 13 g
Water 20 OZ. 600 ccm

This bath must not be used after it has become somewhat brown. After the films are in the fixing bath for a few minutes, daylight or electric light can be turned on and the films washed until all of the unexposed silver disappears.

After fixing, the films are washed for a few minutes in running water, and each in turn is placed in hot water about 120° F. (49 C.). In this bath, the soluble gelatin dissolves, leaving a relief image, which should show clear and colorless edges where the film has not been exposed. If these show patches or streaks of color, or if patches can be seen elsewhere, the water has not been hot enough. The exact temperature, in fact, is by no means important, and a little experience enables one to dispense with a thermometer. Several changes of hot water should be used, until the drainings are free from all trace of color. Veiled whites at this stage indicate overexposure ; lack of detail in the highlights, underexposure.

The image now consists of a gelatin relief containing dye and a black silver image. This silver degrades the color and must be removed. The films should there-fore be placed in a 10 per cent hypo bath, to which enough of a solution potassium ferricyanide has been added to give a strong yellow color, the familiar Farmer's reducer. In this bath, the films will become clear and transparent, and the action should be allowed to continue until all the dark portions, particularly in the shadows, have disappeared and the films are transparent throughout. Wash thoroughly with warm water to remove the reducer, afterwards tranSferring to cold water for a few minutes.

At this stage, the three positives may be superimposed, while still wet, over a light-box, and some idea will be gained of the appearance of the finished transparency. If any one color predominates, the film concerned may be immersed in very hot water, which will reduce it slightly. If this is not enough, add up to 50 per cent of a good grade of wood alcohol to the hot water, when fairly rapid and progressive reduction will result, the film being removed when the desired point has been reached. Trials with the other two films should be made from time to time, in order that the correct balance of color may be secured.

After thorough washing in warm water to remove the reducer, and chilling in cold water, the red and yellow films are treated by bathing them in a solution of

Water 34 oz. 1000 ccm
Potassium permanganate 31 gr. 2 g

for twenty to thirty seconds. They are then rinSed in cold water and placed in a solution consisting of

Water 34 OZ. 1000 ccm
Potassium metabisulphite 1 3/4 oz. 50 g
Hypo 13/4 oz. 50 g

The potassium metabisulphite solution can be used over and over again, but the permanganate solution should be thrown away each time.

After this treatment, all of the films including the blue, which was not placed in the previous solution, are immersed for five minutes in the following:

STOCK SOLUTION

Water 16 1/2 oz. 500 ccm
Acetic acid, glacial 2 1/2 oz. 70 ccm
Copper sulphate, crystals 750 gr. 45 g

WORKING SOLUTION

Stock solution 1 OZ. 25 ccm
Water 20 OZ. 500 ccm

Treatment of the films in the latter solution renders the colors absolutely permanent. Do not use this solution after it becomes blue.

For transfer paper you can use any semi-matte or semi-gloss gelatin-coated paper. Fixed-out (not ex-posed) papers such as Azo F or E, single or double weight, will do. The films are hung up to dry, which may be hastened by means of gentle heat or the use of an electric fan.

Take the yellow positive and a sheet of transfer paper, and place them face upwards in a dish of water and allow to soak for exactly two minutes. Then, beneath the surface, place the gelatin side of the color film next to the prepared side of the transfer paper, removing these together from the water, being careful that no air-bubbles remain between the two sheets. Place on a sheet of glass which is covered with a rubber cloth, and roll with a squeegee to drive out any air-bubbles that still remain, and the surplus of water. Place the transfer paper and color film between a few sheets of damp blotting paper, and leave in a copying press under pressure for about ten minutes. If the worker does not possess such a press, two thick pieces of wood, hinged to open like a book, may be used with clamps around the sides to give the requisite pressure, which must be fairly heavy.

After removal from the press, the tranSfer paper, with celluloid, must be dried, and this may be hastened by gentle heat. When completely dry, the celluloid will strip off cleanly, leaving the yellow image on the paper. Failure of the celluloid to come away readily indicates that drying is not complete. The blue film and the transfer paper bearing the yellow image are now soaked for exactly one minute and brought out, face to face, with precautions against air-bubbles, as previously explained, and lightly squeegeed, the two images then being shifted to coincide exactly, using a magnifier if necessary. The print, now appearing green, is placed between blotters and subjected to pressure in the press for ten minutes. The celluloid will strip off when the print is dry, as with the yellow.

The time of one minute (two minutes with the yellow) for soaking is important, since different lengths of time cause different degrees of expansion of the transfer paper, so that the images may not coincide exactly. When this happens, the celluloid bearing the image should be drawn off under water from the transfer paper, and the latter dried and again soaked, this time exactly. Then proceed in similar manner to transfer the red image, soaking exactly one minute.

In the event you have difficulty with the stripping of the colored pigments to the paper, this can be remedied by the use of a gelatin substratum which causes better adhesion. Prepare this by the following formula:

Water 42 OZ. 1200 ccm
Nelson's No. 1 hard gelatin 1 oz. 30 g

The gelatin should be added to the water and al-lowed to stand several hours, until it has swollen, then warm up the solution by setting it in a saucepan of warm water. When the gelatin is all dissolved, add 6 oz. (200 ccm) of a 2 per cent solution of chrome alum.

Apply a thin coating of this solution to the transfer paper and allow it to dry before using. Repeat the same operation before each color and you will find that this insures clean stripping of the celluloid.

SURFACE TREATMENT.—When the last of the celluloids has been removed, the print will have a very glossy surface. To produce an attractive semimatte effect, soak for two minutes in warm water and dry in cool air.

Bottles of retouching color, which may be mixed to produce any desired tint, are supplied. If any one color predominates in the finished print, this may be corrected by cautiously bathing in a weak solution of the complementary color.

When using Duxochrome transparency film, proceed as above with the following exceptions: The exposure should be about 50 per cent longer, and the developer should be made with 50 per cent more of the A and B solutions, to the same quantity of water.

Because of the thinness of the celluloid base used for transparencies, before hanging them up to dry, it is necessary to treat them in a solution of glycerine, z dr. (7 ccm) and water, 12 oz. (350 ccm) for two minutes. After this bath, they are hung up to dry without further washing in water.

When dry, they are bound in the usual way for transparencies, between glasses, with gummed tape.

COLORSTIL.-This process, distributed through regular photographic dealers, is an American one offered by the Ruthenberg Color Photography Co. of Holly-wood, Calif., and is based on the same patents as Duxochrome. The handling of the material is carried out in the same manner as the instructions given in the foregoing text on the Duxochrome process, viz.: Development of film; Fixing; Removal of unhardened emulsion; Removal of black silver; Drying; Transfer of images to paper support.

There have been a number of improvements in Colorstil which are explained in the leaflet supplied with each package. This material comes prepared in standard packages, with all materials necessary for making four 8 by 10 color prints.



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