Color Photography - Screen Color Transparencies
( Originally Published 1938 )
THESE are methods of making by one exposure 1 a negative which, when developed, can be reversed into a colored positive.
AGFACOLOR ULTRA PLATES.—These are glass plates coated with a screen consisting of numerous tiny particles of transparent material dyed with the three primary colors: blue, green and red. The particles are extremely small, so that even on projection of the finished plate, they are scarcely discernible. The color particles act as a mosaic of minute color filters in perfect balance, through which the exposure is made. The color screen thus obtained is given a very thin insulating lacquer coating, and over this is flowed the special panchromatic emulsion which is made for the plate.
Thus, when the plate is placed in the camera with the glass side toward the lens and exposed, the light passes through the color screen first, before it strikes the sensitive coating. When this takes place, each of the small color particles in the screen acts as a tiny filter on that portion of the sensitive coating just be-hind it. Upon development as a negative and reversal into a positive, the original colors of the subject photo-graphed are faithfully reproduced.
Following you will find the outline of the steps involved in the exposure and development of these plates. A booklet entitled Agfacolor Ultra Plates can be had from your dealer or the Agfa Ansco Corporation of Binghamton, New York, without charge.
In order that the light from the subject shall first pass through the filter coating before reaching the emulsion, the plates are loaded in total darkness, glass side out in the holders. A black card which comes with each plate is placed between the emulsion face and the back of holder. This protects the face of the emulsion while in the holders. Keep it against the face of the emulsion at all times until ready for development.
The plates should be removed from the box and loaded into the holders in total darkness.
The ground glass focusing screen is reversed to bring the focusing plane into agreement with the plate emulsion, or the lens can be racked slightly back (1/16-inch) after focusing.
COMPENSATING FILTERS.—In order to compensate for the difference between the actinic and visual value of the colors in the light it is necessary in some cases to use compensating filters. Below we give a table showing when the filters are needed and the correct ones to use under various light conditions:
KIND OF LIGHT COMPENSATING FILTER REQUIRED
Normal daylight None
Blue Mazda bulbs should not be used with Agfacolor Ultra plates.
EXPOSURE.—Agfacolor Ultra plates require about six times normal black-and-white exposure. Because of the increased speed of the new Agfacolor Ultra plates the length of exposure necessary has been again reduced. Instantaneous exposures may now be made without trouble in sunlight, for the Ultra plates have about 1/6th the speed of a high-speed orthochromatic roll film such as Plenachrome. A scene, for example, which requires an exposure of 1/ 150th second at f:6.3 on Plenachrome film may be photographed on an Agfacolor Ultra plate at 1/25th second at f:6.3. Those who are accustomed to working with the older type Agfacolor plate will find that 1/5th the exposure formerly necessary for the Agfacolor plate is now sufficient for the Agfacolor Ultra plate.
Fairly accurate exposure is more important in color plate work than in black and white, for a reason that is readily perceived. In black and white, if the negative is too contrasty on the one hand or too weak and flat on the other, compensation can be made in printing. With color plates, this compensation is not possible, for both negative and positive images are produced from the same emulsion layer—a condition which requires a correctly exposed negative image for best results. Nevertheless, exposure for good results is by no means difficult, and with ordinary care good results can be expected from the start. The point is that one should not expose carelessly without attempting to estimate the value of the light.
Because color plates involve the process of reversal, the effects of underexposure and overexposure are just the opposite of what would be expected. Under-exposure, such as would make a thin negative in the shadows in black and white, produces in color plates a heavy, dense transparency, in which the colors may be unnaturally dark. On the other hand, over-exposure, such as produces strong, dense black and white negatives, will, with color plates, produce a transparency too thin and weak, with colors that look washed out and lifeless by transmitted light.
USE OF PHOTOFLASH BULBS.—The Photoflash lamp has very real advantages in color photography, the greatest being that each lamp represents a unit of illumination that may be definitely counted and multi-plied as the subject may require. When the number of lamps required for a certain type of subject at a certain diaphragm opening has been determined, further exposures can be made on a similar subject with a certainty of obtaining exactly the same quality of result. The filter recommended for Photoflash is Agfacolor Blue Filter No. 24.
These exposures assume the use of the blue (Agfa No. 24) filter over the lens and reflectors behind No. 20 Photoflash lamps. If No. i0 Photoflash lamps are used, give one stop greater exposure; if No. 75 Photo-flash lamps are used, give two stops less exposure. If extra reflectors are used or if the subject is prevailingly light in color, somewhat less exposure may be given, but if the subject is rather dark and no extra reflection of light is obtained from walls or extra reflectors, it is advisable to increase the expo-sure considerably.
Photoflood lamps may be used according to the table below, bearing in mind that the value of the lamps will change (become slower) as they get older and become discolored. With the Photoflood the Agfa Blue No. 24 filter is used. The table given is based on the use of No. i Photofloods in reflectors. Larger size will decrease the exposure. For accurate exposures Photoflood exposure time should be checked with a photo-electric meter.
ARC LIGHT.—Because of so much variation, the arc lamp is not as useful as the Photoflash and Photo-flood. Exposure time must be checked by meter.
DARKROOM ILLUMINATION.—The emulsion of the Agfacolor Ultra Plate is panchromatic. That is, it is sensitive to all colors of the spectrum, even to red. Care must therefore be taken in exposing these plates to light of any kind, and it is better to keep them in entire darkness at least until the commencement of development. Whatever light is used, it should be spectroscopically safe and of a green type. A light of any other character, especially red, will immediately fog the plate.
The Agfa No. 108 green safelight may be used with a ten-watt lamp provided the light ray does not fall directly on the plate.
Development of the Agfacolor plate is complete in three short operations:
1. First development brings out the negative image as in black and white work. Note that this operation is development only; there is no fixing or clearing of the plate with hypo. A short rinse in cold water should follow first development.
2. Reversal, which is accomplished by transferring the plate to a bath which attacks the blackened silver, eating it out, and then by turning on the white light to expose the balance of the emulsion (which may be thought of as that part which in black and white work would be cleared away by the hypo). A short rinse in cold water should follow the reversal operation.
3. Redevelopment in the original developer, to blacken the part of the emulsion unexposed in the camera, but exposed in the reversal process.
The result is a positive correlated to the color screen in the plate, through which the original exposure was made and through which the image is viewed by transmitted light.
PREPARED DEVELOPER AND REVERSER.—In the following detailed instructions, formulas are given for compounding the developing and reversing baths, but for those who do not wish to go to this trouble a complete developing set consisting of developer, reversing bath powders and a small bottle of varnish can be purchased.
FIRST DEVELOPMENT.—Agfa No. 96 Agfacolor Developer. If you prefer to compound your own developer, do so according to the following formula.
Metol 48 gr. 3.3 g
(Do not dilute for use)
In ordering ammonia, ask for specific gravity .91 or with ammonia content 25 per cent by weight.
The developing solution is now complete, but it is advisable to filter it before use.
About two ounces of the solution is sufficient for one 3 1/4 by 4 1/4 plate. Since the bath loses energy in development and is later rendered impure in the redevelopment of the reversed plate, every plate must have fresh developer for the first development, and the temperature as used should not be allowed to exceed 65 ° F. (18 ° C.). This is very important, especially in summer, as too warm a bath develops too quickly and may cause frilling and pinholes.
If the plate is correctly exposed, development will be complete in approximately four minutes.
Development (unless desensitizer is used), and all manipulations up to the time of turning on the white light in reversal, must take place either in darkness or with the Agfa safelight No. 108 (green) in the darkroom lamp. To the direct rays of even this light, however, the plate should not be exposed very long. The best way is to place the light so that the developing tray is in shadow, but the dial of the clock is in the direct rays and visible as development proceeds. The plate can then be held up from time to time for brief inspection. Any other source of light than that mentioned (especially red light) will immediately fog the plate.
CONTROL OF DENSITY BY DEVELOPMENT.—First development converts the exposed silver bromide grains in the sensitive coating to metallic silver, that is, it blackens them, leaving the unexposed silver bromide grains unaffected. When, next, the plate is placed in the reversal bath, this bath removes the metallic silver. The reversal bath does not, however, affect the undeveloped silver bromide grains. Therefore, when the reversing bath has completed its action, a strong white light can be turned on to expose the silver bromide grains that were not exposed in the camera and there-fore not developed or blackened, and for this reason not affected by the reversal bath.
Reversal has now removed the negative image, and secondary exposure after reversal has produced a latent positive image. Second development converts the exposed silver bromide grains of this positive image to metallic silver, thus forming the visible positive image.
It has been found that a normally exposed color plate which has been given four minutes first development will reverse out just enough silver to leave the amount for secondary exposure and second development required to make a perfect positive image for the finished plate.
If, however, the plate has been overexposed, then four minutes of first development will blacken too much silver, causing too much to be reversed out and correspondingly too little left in for the positive image. Likewise, if the plate has been underexposed, four minutes of first development will blacken too little silver, too little will be reversed out, and too much will be left in for the positive image, so that the latter will be over-dense.
Therefore it is desirable to shorten the first development of overexposed plates and lengthen the first development of underexposed plates, which can be done quite accurately by utilizing the factorial system of development explained in the following paragraph.
FACTORIAL SYSTEM OF DEVELOPMENT.-This system iS based on observation of how long it takes for the general outlines of the picture to appear after the plate has been placed in the developer. The time will naturally be longer with underexposure, and shorter with overexposure, and the total length of development necessary can be gauged accordingly.
To allow sufficient illumination for inspection of plates when the factorial method of development is used, plates should be bathed before development in a solution of pinakryptol yellow desensitizer. This treatment permits the use of brighter safelight illumination (Agfa Safelight Filter No. 103 with a z5-watt lamp) placed at least two feet from the developing tray. The desensitized plates may be safely exposed to the direct rays of this safelight during the course of development.
Plates should be immersed in the pinakryptol yellow desensitizer for two minutes in total darkness, after which time the safelight described above may be turned on.
PINAKRYPTOL YELLOW DESENSITIZER
Agfa pinakryptol yellow 15 gr. 1 g
Dissolve the desensitizing dye in the water, which should be boiling. After cooling, add the alcohol and use at 65° F. (18° C.).
Upon removal from the desensitizer, plates should be rinsed in water for exactly thirty seconds prior to development. As soon as development is started, watch for appearance of image while rocking the tray gently. The following table indicates the proper developing time at 65° F. (18° C.) for the corresponding time required for the general outlines (ignoring brightest highlights, sky or horizon) of the negative image to appear.
When development has been completed, wash the plate for about one minute in running water. A gentle spray may be used, or the plate moved about in a large tray into which a stream from the tap is running ; but do not let the stream fall directly on the coated side of the plate, as the emulsion is delicate and easily damaged.
After rinsing as above, put the plate into the reversing bath made up as follows:
Water 32 oz. 1000 ccm
(Add acid to water while stirring slowly)
For use take ten parts water and to this add one part stock solution. Of the dilute solution thus obtained, about 2 ounces (60 ccm) will be required for one 3 1/4 by 4 1/4 plate. The temperature should not be allowed to go higher than 65° F. (18° C.), as the emulsion may otherwise leave the plate.
In this solution more than one plate may be reversed; and the solution is usable as long as it is not too muddy or of a greenish tint.
After the color plate has been in the reversing bath a few seconds, normal white light may be turned on in the darkroom.
As soon as the blackened silver in the emulsion is completely eaten out, as may be judged by transmitted light, remove the plate from the reversing bath and wash it for about two minutes in running water. It is then ready for redevelopment.
Place the reversed plate in the original developing bath and turn on a strong artificial light or take the tray with the plate in it into diffused daylight. This necessary step gives the plate its secondary exposure. A Photoflood lamp, located about two feet from the tray, makes an excellent type of illumination. Leave the plate in this bath as long as is necessary to make the film appear absolutely black. Redevelopment will usually be complete in about two minutes. The bath used for redevelopment cannot be used again for first development, and it should be thrown away.
Now give the plate a quick rinse in water, perhaps half a minute, and dry it immediately and as quickly as possible, preferably in a gentle current of air from an electric fan. If drying is delayed or prolonged, green or brown spots may form in the color screen of the plate. Do not, however, attempt to hurry drying by applying heat, or by using an excessively warm current of air.
When the plate is thoroughly dry, the colors which in the wet plate appeared somewhat rough and washed out will show brilliant and clear.
Varnishing is not essential, but is recommended as a protection for the delicate film, preventing injury from finger marks, etc., in handling, as the varnished surface can be wiped off with a soft cloth. The best varnish is a solution of three parts gum dammar in a hundred parts benzol. Pour a small quantity on the thoroughly dried emulsion, and by tilting the plate cause it to run all over the surface without forming lines. If too much solution has been poured out, the surplus can be run off at a corner of the plate back into the bottle.
The edges of the plate can now be bound up, and the coated side still further protected, if this is desired, by binding a cover glass to it.
INTENSIFICATION AND REDUCTION.—As in the case of monochromatic photography, it is possible either to intensify or to reduce a color plate (before varnishing, of course). Further handling of the plate, however, should be avoided if possible, as it does not always give satisfactory results.
If the color picture is too light and too trans-parent, due either to overexposure or to overdevelopment, it is possible that intensification may increase the blackening and bring about a greater brilliancy of the colors.
While in most instances it will not be necessary, finished color plates can be intensified or reduced to correct exposure errors. A plate that appears too thin, transparent and weak in color may be considerably improved in density and brilliance of color by after treatment in prepared Agfa Mercury Intensifier. The mercury solution is diluted with nine parts of water and gives direct intensification without subsequent treatment. Plates are immersed in the solution and inspected frequently until intensification is judged complete, when they are washed for a minute in running water and dried rapidly. The following intensifier may also be used, although it is not subject to the control over intensification afforded by the single solution Agfa Mercury Intensifier.
Potassium bromide 1/4 oz. 35 gr. 10 g
Plates are immersed in this solution about two to three minutes at 65° F. (18' C.) until grey in appearance and then washed in water containing a few drops of hydrochloric acid. Intensification is obtained by redevelopment in regular color plate developer.
Reduction of color plates, though not as satisfactory a treatment, may be used to lessen the density of underexposed plates. For this an extremely dilute solution of reversing bath, of about one part stock solution in one hundred parts water, may be used, or, if preferred, Farmer's Reducer may be employed. After reduction to the desired density, plates should be washed and dried as usual.
The Agfacolor booklet lists a complete table of many other variations and remedies to which we can-not give space here. This book may be had gratis from your dealer or Agfa Ansco Corporation, Binghamton, New York.
SEPARATION NEGATIVES FROM AGFACOLOR ULTRA PLATES.—TO those wishing to make separations from Agfacolor Ultra Plates the writer suggests they try Agfa Isopan Cut Film with the sharp contrast filter method in the same manner as outlined on page 157 for Lumiere Filmcolor.
LUMIERE FILMCOLOR.—The Lumiere Filmcolor, formerly sold under the trade name of Autochrome, is probably the oldest film of this type on the American market. Formerly made on glass, they are now supplied on a film base only.
Filmcolor is a single film with two distinct coatings, one a color screen containing about 7,000 assorted tricolor starch grains to the square inch, which act as separation filters, and the other a panchromatic emulsion.
This has a much greater speed than the old product, requiring 12 times the exposure given for a Weston plate speed of 8, or 12 times a Scheiner speed of 17. Snapshots may now be made upon it with fast lenses. The same filters and developing technique are used.
The films come packed four to a box in a variety of standard sizes. Each film is in a folded paper, black inside and white outside.
The film with its paper covering is held in the right hand, with the corrugated end under the thumb. Slide the paper and film into the sheath or holder, face down. When in place, tear off the top sheet of paper with the corrugated edge (which will leave the celluloid or back of film facing the lens) and replace the slides.
Because of the fact that the blue and violet rays of the spectrum act too strongly on the panchromatic emulsion, it is necessary to use a Filmcolor filter over the lens to properly balance the colors.
Different filters are provided for various sources of light, such as daylight, Photoflood, Mazda and flash-light powder. Be sure you use a filter sold by the manufacturer for the purpose.
At stop f : 16, outdoor exposures will run from one second on a bright sunny day to six seconds on a gloomy day. In the studio, exposures will vary according to the light used. Tests will have to be made under your own working conditions. The speed designations of this film will be found in the instructions of all standard exposure meters. A photo-electric meter is recommended. Twelve times the exposure that would be given for portrait par speed film is required.
FIRST DEVELOPMENT.—COLOR film should be developed in the dark or with the use of Virida paper sup-plied for this purpose. Expose as little as possible even to the light of the Virida paper. Use glass or white enamel trays that are clean and free from nicks or rust spots. The developer can be purchased ready-made or can be made as follows:
METOQUINONE STOCK SOLUTION
Distilled water 35 OZ. 1000 ccm
The metoquinone powder should be dissolved first in two-thirds the quantity of water, which is heated to the boiling point. After the metoquinone is thoroughly dissolved, add the other chemicals in the order given, adding the other one-third of cold water just before the ammonia is added.
This first development should take about two and one-half minutes at 65° F. (18° C.) or a factorial system can be employed, by watching the time the image first takes to appear (disregarding the sky) and multi-plying this time by ten to arrive at the total development time necessary for this particular exposure.
REVERSAL.—After the first development, the film is rinsed in water for about a minute and is then placed without fixing into the reversal solution, which can also be bought ready-made or made up as follows:
Water 35 OZ. 1000 ccm
As soon as the film is in the reversal solution, it is exposed to daylight or Mazda light. In this solution the film clears progressively, showing the colors, al-though the silver does not yet turn black. This operation is complete in three or four minutes. If not thoroughly cleared, black spots and streaks will occur later. As soon as action is complete, rinse for about forty seconds in running water and you are ready to proceed.
After reversing by exposure to daylight or artificial light, put the film back into the first developer, which should be kept for this purpose. In this developer action will be completed in three or four minutes, or when the white part of the image turns completely black. At this point you cannot overdevelop.
The film is now rinsed for two or three minutes and placed to dry without fixing. As soon as it is dry, it is varnished with Filmcolor varnish and is then ready for inspection. After varnishing, the film can be bound between two glasses.
To avoid frilling in hot weather, the following re-developer is recommended instead of using the first developing solution. It can be bought ready-made in tubes or made up as follows:
Water 16 oz. 500 ccm
Leave in this solution for three or four minutes, then wash for one or two minutes in gently running water and put to dry.
If, after the second development, the film does not show sufficient contrast, it may be improved by intensificationeither at the time or after it has dried.
Water 4 OZ. 100 ccm
Cover the film and rock the tray. When bright enough, put the film in the dianol developer mentioned above, or any other non-alkali developer, for about five minutes. Then wash for several minutes and dry. The above intensifier will not keep from day to day, but may be used for several films at one time.
OTHER HINTS ON FILMCOL0R.-Underexposure will give practically no detail in shadows, but too great a general density dominant in blue.
Overexposure gives a weak image, with poor contrast, but quite transparent.
Other causes of bluish tinge are:
1. Failure of the filter to exclude all light except that passing through it. A poorly fitting filter which lets in light around the edges will do this.
2. No filter at all will give an entirely blue image on account of the preponderance of blue and violet rays.
Fogging: If fogging is caused by light coming through the back of the film, through the surface of the starch grain and emulsion, it will be noticed mostly in the shadows and will be of a shade corresponding to the color of the light which caused it. If it is caused by light coming through the front or emulsion side of the film, a black fog will result which, when reversed, will cause the film to be weak and flat.
Frilling: Keep all solutions at 65° F. (18° C.). Avoid sudden changes in temperature. During the time the film is drying, pick up the surplus water along each edge with the side of a blotter. This prevents frilling, and green edges when dry. If the weather is warm and you are afraid of frilling, you can dry the film after reversal and complete the treatment later.
DUPLICATING FILMCOLOR BY CONTACT.—A reproduction screen is supplied for this purpose by the manufacturers. The duplicating screen is placed into or in front of a printing frame, directly in front of the Filmcolor to be duplicated. The Filmcolor must be placed in the frame with the back facing the screen. In the darkroom an unexposed Filmcolor film is placed with the back next to the emulsion side of the Film-color you are going to duplicate, taking care to remove the paper only from the back (celluloid) side, leaving the black paper protector on the emulsion side, which will come next to the back of the printing frame when closed.
The duplicating Screen does not need to be attached to the front of the frame, as long as it is so arranged that the light reaching the Filmcolor you are duplicating passes through the duplicating screen.
Exposures will average from three to five seconds, about two feet from a 40-watt lamp. The developing and finishing is carried on as in the making of the original.
MAKING SEPARATION NEGATIVES FROM FILMCOLOR.
If from a finished Filmcolor transparency you wish to make a set of separation negatives in order to make paper prints or transparencies by methods outlined in this book, you may do so by contact, using a set of what are known as narrow cut filters. With Wratten and Wainwright or other Eastman plates, Wratten filters No. 29F red, No. 61N green and No. 50L blue are used. With the red filter a panchromatic plate is used, with the green an orthochromatic, and with the blue a color-blind plate. Bear in mind when developing such separations that you are making negatives which should be moderately soft, with detail in the shadows. If sensitized material other than Eastman is used, find out from the maker or importer what narrow cut filters are necessary for this work.
In making such separations, the screen plate is placed emulsion to emulsion with the copying plate, with a sheet of thin clean glass or celluloid between them, in order to avoid reproducing the screen or mosaic pattern. The exact thickness necessary to get a continuous tone effect will be found with one or two trials. The transparencies should be loaded into a holder of some sort (similar to the Finlay holder) with the copy plate. This is placed at one end of a light-tight black box or back of camera. At the other end of the box or camera, about twenty-four inches away, the proper narrow cut filter is mounted. In front of the filter a cardboard with a circular opening (lens re-moved) covered with a piece of groundglass is mounted. The size of the circular opening, the thickness of the medium between the plates, the distance of the light, the length of the box (or bellows draw)—all enter into the quality of the resultant separations. Wall gives in his "History of Three-Color Photography," page 544, details of how to arrive accurately at these factors. The exposure is made with the small source of white light which will evenly illuminate the circular groundglass opening. One or two trial exposures will have to be made to find the correct time. Start with approximately two minutes.
The negatives obtained by this method should be developed and printed with the same attention to balance and other details as outlined under the making of separation negatives.