Color Photography - Belcolor Printing Film
( Originally Published 1938 )
FOR making contact transparencies from separation plates, Belcolor undoubtedly offers the simplest and most practical method. Calling for no special workroom condition or expert technique, it can be used successfully without the practice necessary in other processes.
The material consists of sheets of thin celluloid coated with an unsensitized layer of colored gelatin in the complementary colors, red, blue and yellow. Special colors, such as black for four-color and trans-parent yellow for slides, are also available. Belcolor transparencies are made regularly as engraver's proofs in sizes up to 19 1/2 by 23 1/2, the full size of the sheets.
These sheets, one of each color, are sensitized in a solution of potassium bichromate as outlined below and printed through the film side in contact with the separation plates, giving a beautiful transparency in colors. Belcolor film will curl and become brittle if stored in a hot, dry place. Keep in a moderately cool room.
SENSITIZING AND DRYING.—We give below two formulas, one with all water for normal work and one with Columbian spirits (a good grade wood alcohol) for quick drying. Sensitize in a cool but not a cold air-conditioned room, for if the sensitizer is too cold the bichromate will precipitate and cause grain.
Water 35 oz. 1000 ccm
QUICK DRYING FORMULA
Water 25 OZ. 700 ccm
In cold dry weather increase the water and decrease the alcohol by the same amount or use the regular formula.
Note: Use the regular formula (without alcohol) whenever possible, as it will give a finer grain Belcolor than the alcohol sensitizer.
If three clean trays, slightly larger than the sheets to be sensitized, are available, place them in a row in a dimly lit room, using a yellow light similar to that used for bromide paper. (These same three trays can be used later for development or, if only one tray is available, one sheet can be sensitized at a time.) Pour a moderate amount of sensitizer which has been cooled to 60° F. (16° C.) into each tray. Use a clock for checking the time. Slide one sheet of color face up into the first tray, rocking it so that it is thoroughly covered. At intervals of one minute each, immerse the remaining colors in the trays. At the expiration of three minutes, take out the first sheet, lay it face down, glossy side up, on a sheet of glass (this glass must also be cool to avoid melting of pigments), and draw a flat rubber squeegee lightly across the back to remove the surplus solution. A damp swab of cotton can be run over the back at this stage to remove the surplus solution, which will save cleaning later. Pick up carefully by one corner, turn face up, and pin at each corner to a board or sheet of corrugated board. A sheet of lintless blotter between back of color sheet and board will prevent uneven drying and avoid water spots on back. The Belcolor is then placed face out on a shelf in a darkroom and a fan placed where it will blow on the sheets and dry them evenly. Successive sheets are handled in the same way after three minutes in the sensitizer.
Drying is the most important part of the process and must be carried out quickly and evenly. With the alcohol bath the sheets will dry in about thirty minutes. With the regular water sensitizer, it should take about an hour.
If drying is unduly delayed, the pigment will become tough all over, or possibly only in the spots which dried last, and will develop unevenly when printed. A drying cabinet which will circulate air and at the same time keep out the dust should be built by regular users of Belcolor.
When thoroughly dry, lay each sheet down on a clean piece of paper, hold carefully to avoid buckling, and with a slightly moistened cotton swab go over the back. With another dry swab, polish until back is clean. This is necessary, as printing is done through the back of the celluloid. Store in envelopes between corrugated board, in a moderately cool place. If stored in a hot dry place, it will curl.
For best results, printing should take place four or five hours after drying, or at least the day following. Freshly sensitized sheets will develop in water of a lower temperature, which keeps the detail fine and soft. The film can be used for several days after sensitizing, but will require hotter water to fully dissolve the loose color.
Before starting to print the Belcolor film sheets, the density of the negatives should be checked for the approximate printing time. An arc lamp or Cooper Hewitt tubes are the most reliable printing lights, al-though Photoflood or large Mazda bulbs can be used. Cooper Hewitts remain more constant as a light source. Take the negative made through the A (red) filter, which is the blue printer, and expose behind this in a regular printing frame a piece of ordinary proof (printing-out) paper. If the negative has a grey scale wedge included, expose until the lightest or white step just begins to grey. If no grey wedge is included, select some portion of the negative which you know to be white or nearly white and print the same as out-lined.
The time taken to print the proof sheet by any given light will be approximately the correct printing time for the color sheets when they have been freshly sensitized with the formula given above.
Each color will require the same printing time if the negatives are correctly balanced. If the negatives have grey scales which appear to be of different densities, each must be tested separately with the proof paper for relative density, or with a little experience this can be judged without the test. In general the red and yellow printers will stand a little more and the blue a little less than the test time, as the blue washes down faster than the blue and yellow.
After deciding on the proper exposure time, each color sheet is exposed with the back or shiny side next to the face of the negative. No border or mask is necessary. It is best always to work in the same order, blue, red, yellow, corresponding to the A, B, C filters. Work in a subdued light when loading and unloading the printing frame. A good method is to have two large brown envelopes, one for the unexposed and one for the exposed film.
The short time in the subdued light while loading the frame will not affect them. A sheet of medium weight cardboard or felt can be placed in the frame between the back and the film in order to insure good contact. The exposed sheets are now ready for development.
DEVELOPING AND CHECKING COLORS.—FOE the best results three trays a trifle larger than the color sheet should be provided, in which the hot water—about 105° F. (410 C.)—for developing the film is placed, also one larger tray of cold water and one of lukewarm water. Of course the films can be successfully developed one after the other, using the same tray, but the problem is much Simpler with the three trays. The cold water should be quite cold. If warmer than 65° F. (18° C.) a piece of ice can be used to bring the temperature down.
A clip, metal or wood, is now attached to the end of each exposed film to act as a handle (to keep the warm fingers from softening the color), and each color is slid carefully face up into a separate tray of hot water about 105° F. (41° C.), rocking the tray and shaking the sheets back and forth by means of the clip. In a few seconds the colors will begin to loosen, allowing the color not made insoluble by the action of the light and bichromate to wash away. As soon as the image appears to be cleared up, rinse the sheet in the luke-warm water, chill a minute in cold water, and examine by holding up to the light or by laying face up on a light box (to be described later). Preliminary development should be carried (that is, the color is washed down) until the first step in the grey wedge 0r some known white portion or the negative is clear. The sheet is then placed in the cold water, which stops the development.
When the sheets are not used soon after sensitizing, the yellow (and in rare cases in hot weather the red and blue) do not start to wash promptly in the hot water. In such cases have handy a bottle with a 5 per cent solution of sodium carbonate (1 ounce (30 g) carbonate, 20 ounces (560 ccm) water) and add one-half to one ounce of this solution to 64 ounces (a liters) of hot water. Hold the film up by the clip until it has been thoroughly mixed with the hot water, then return the film, and the colors will develop with-out trouble. In such cases the top layer of pigments usually comes off in small chunks instead of loose color. Do not use more carbonate than necessary, as it will cut down the film too fast or unevenly if too strong.
When each color is developed and has been transferred to cold water, you are ready to preview or check the color balance. For this purpose you should have a box or table with a light under flashed opal or ground glass. A printing machine with not too many bulbs will do. Pick up the celluloid with the yellow image from the water and slowly lay it face down from one end to the other on the glass. At this point, if you have an assistant or some clamp arrangement to hold it from slipping, it will facilitate registering. If someone will stand behind the box and hold the corners with the thumb nails, you can then pick up the red film and lay it face down over the yellow one, sliding it around a little to complete the registration. While you hold it in place, your assistant transfers his hold to the top or red sheet. The blue is next brought over and matched in the same manner.
Now you can stand back and examine the complete color transparency. If this is correct, which it will be provided your negatives are balanced, it is only necessary to replace the sheets one at a time in the cold water and take them one at a time in the small trays to the sink and wash well to remove surplus color, being sure to carefully rub the back or the unsensitized side of the film with the fingers or cotton to remove any color that may have come from registering. Face of the film must not be touched with the fingers, but can be held at an angle under a gentle stream of water.
If, however, on examining the film on the registration desk you find the entire subject too dark, or any one color too dense, you remove this particular color to the hot water (a fresh batch, leaving the others in cold water in the meantime) and proceed to wash it down and then re-examine the complete pictures as outlined above. The carbonate solution can also be used at this time to force any one color down if it does not respond to the hot water, which can now be used at even higher temperature (about 125° F.) (52° C.) than before. Belcolor film does not frill from its base, so no fear need be felt on this point.
The films are dried by hanging up on a line and al-lowed to dry of their own accord, or they can be dried quickly with a fan, being careful that they are not hung too close together while wet. To hasten drying, the back or shiny side can be mopped off carefully with a dry cotton swab to prevent wet spots, which retard the drying of the face.
REGISTRATION AND MOUNTING.—After the color films are dry, a strip of Scotch masking tape is attached to the top of each film, allowing a portion of the adhesive strip to project beyond the edge of the film. The yellow is now placed on a sheet of flashed opal glass of the approximate size of the film, which is laid on the registration box with a light underneath. A quick rub across the top will cause the tape to adhere to the glass. This is repeated with the red and finally the blue, registering carefully with a magnifier each time. When the three are in position, bound together at the top, a slip of tape is attached across the bottom of the film and fastened in position at the back of the glass to hold the separate films from slipping. Next a clear, clean glass of the same size is bound over the film and flashed opal glass in much the same manner as a lantern slide is bound. This holds the film in position and protects its surface. The transparency in natural colors is now complete.
Belcolor sheets come in three sizes, 4 by 7 1/2, by 9 3/4. and 19 by 23, and will keep indefinitely before use. Keep in a cool, dry place. Too much heat will cause them to curl up, in which case they should be placed in a damp location and flattened out again.
STRIPPING BELCOLOR FOR PAPER PRINTS.—AS we write this book (1937) the manufacturers of this material are beginning to supply the same material as above, except that it can be finally stripped in register to paper in the same manner as the Carbro and Duxochrome. This is still in the experimental stage, but may be fully developed by the time you are reading this chapter. We suggest that you inquire of your dealer for further data.
THREE-COLOR GRAVURE POsITIVES BY TRANSFORM-ABLE NATURAL COLOR FILM (BELCOLOR).—This is a method of making and balancing color positives from separation negatives and transforming these color positives into the equivalent of black-and-white positives, retaining the same proportionate tone value as in the color positives.
These black-and-white positives can then be printed on carbon tissue resists for color printing, without the necessity of balancing the negatives or positives by hand.
The sensitizing, drying, printing and developing of the transformable film is carried on in exactly the same manner as the regular Belcolor (non-transformable) film, up to the point where the final examination of the chilled sheets over the flashed opal glass has taken place.
When dry, they are again soaked in cold water for about five minutes, after which they are placed for three to five minutes (longer will not harm) in the following solution:
TRANSFORMING DEVELOPER FORMULA
Water 34 oz. 1000 ccm
For normal results add to the above 34 ounces (1000 ccm) of 20 per cent solution of potassium carbonate.
For contrasty results add 32 oz. (900 ccm) of a 1 per cent solution of caustic soda.
Wash five to ten minutes in cold water to remove developing solution, and dry. The sheets will then have a blackened appearance, showing the colored effect caused by the blackening of a silver layer contained in the sheets. These black tones, added equally to all colors, give them the black and white printing quality for carbon resist printing.
The principal advantage of making a positive by this method is that in the original washing out of the color sheetS in the hot water, slight variances in exposure or development can be adjusted by washing some colors more than others. The actual color job can also be visualized before converting to black and white.
If one desires to keep a color positive for a guide, two sets can be made and one kept in color, while the other is made into black and white.
In this case the extra set can be made on the regular (non-transformable) Belcolor film, which is less expensive, or if made on the transformable film it can be made permanent in color, without danger of subsequent darkening, by fixing for five minutes in a plain hypo bath (1 oz. (30 g) hypo to 8 oz. (220 ccm) water), which will fix out the layer of silver which is in the film.
BELCOLOR SOLUTION.—Since the first edition of our book was published the Belcolor people have begun to supply in liquid form emulsionS such as are coated on the regular Belcolor film. This liquid emulsion can be coated by means of a whirler on to sheets of celluloid by the user himself. The advantage of the new liquid material is that it can also be stripped off on to paper.
Information on the use of this material can be had through your dealer or direct from the American Importers of the Belcolor Products, George Murphy, Inc., 57 East 9th Street, New York City.