Color Photography - Making Color Separation Negatives
( Originally Published 1938 )
IN AS MUCH as this book is written for the professional or advanced photographer, we assume that he already has a rigid studio or view-type camera with an equally rigid stand. These will be sufficient to start with for still life subjects. Select three plate holders that are of exactly equal depth from the outside of the holder to the emulsion side of the plate, using these exclusively for your color separation work.
If films are used, the films in their holders should be acclimated to the atmosphere of the studio before any exposures are made, otherwise unequal absorption of moisture may cause buckling of one or more of the films, resulting in pictures both out of focus and out of register.
A standard motion picture type tripod iS good. Re-member, the slightest change in position of the tripod or camera during the time a set of separation negatives is being exposed will ruin the entire set of negatives.
It is advisable to lock all adjustments on the camera and tripod before starting to expose the three plates. Sometimes it is even necessary to build braces from camera bed to tripod legs to add to the general stability.
When using a semi-rigid view-type camera a brace of some sort reaching from the front to back of camera should be clamped in position to keep the front and back of the camera absolutely rigid and parallel. Brass rodS on each side which slide in an eye, with thumb-screw lock, will accomplish this purpose.
REPEATING OR SLIDING BACKS.—These are backs which can be attached to your own camera, which are so arranged that you can load the three plates at once. The appropriate color filters are built into the back, each sliding into place in front of its respective plate as the exposures are made. Such backs slide from side to side or up and down in order to expose the three plates successively and with as little loss of time as possible. Some are pushed across by hand, others are operated mechanically in conjunction with the same cable release which operates the lens shutter, the successive plates moving automatically into position between exposures. With some types of automatic backs the operator controls the exposure with the release, holding it down for each exposure, the next plate moving into position as the release is operated. On another type, dials are provided so that the time for each plate is set in advance, one pressure on the release operating the shutter and back for all three exposures.
A repeating back is indispensable in photographing certain food-stuffs, flowers, or any subject where one has to work with a certain amount of speed. It saves the time and bother of having to change plate holders and filters.
ONE-SHOT DOUBLE MIRROR COLOR CAMERAS.-For successful fashion or advertising work with live models or other subjects, where fast exposures must be made to prevent movements, a one-shot camera iS a necessity.
Details of construction of such cameras will be found in several technical books on color, such as Wall's "Practical Color Photography" and "History of Three Color Photography" (both now out of print, although copies can be found at many public libraries or camera clubs).
ONE-SHOT SINGLE MIRROR COLOR CAMERAS.—In addition to the type of one-shot cameras which make the separate negatives each in a different plane by reflected and transmitted light, there is also in use a similar type of one-shot camera which makes use of two films face to face in one position and a single film in a different plane. Cameras of this sort are simpler to construct, requiring only one reflector-transmitter. In some cases they are so arranged that the back or slightly soft film in the bi-pack combination is the blue printer (red filter) and in other types the rear film is the red printer (green filter) negative.
Plates are preferred by most workers on account of their rigidity, but since the first edition of this book was published films have become more generally used, chiefly on account of the single mirror type of camera. When using film, care should be taken to develop, fix, wash and dry all three films under the same conditions, hanging them always one way, which will minimize the possibility of irregular stretching.
TRI-PAC FILM.—Since our first edition a film assembly known as Tri-pac has been put on the market by the Defender company, This assembly consists of three films loaded together in a single pressure back holder.
The front film is blue-sensitive. It is loaded back (non-sensitive) side toward the lens. Directly behind it, emulsion to emulsion, is the green-sensitive film.
The first (blue-sensitive) film contains a yellow dye which acts as a filter to the green-sensitive film.
The third film (red-sensitive) is panchromatic and is loaded emulsion side toward the lens. The light reaching it is filtered through a red coating on the back of the second (green-sensitive) film. The first two films are perfectly sharp, the back film is slightly diffused.
When used with Photoflood or Photoflash lighting, no compensating filter is necessary. With daylight a Wratten 8-B Filter is used.
Allowance should be made for the glass in holder by reversing the camera ground-glass. The separate units of the Tri-pac film can also be used separately in single mirror one-shot color cameras. Speed of the Tri-pac film by Photoflood is Weston 3, by daylight with Wratten 8-B Filter, Weston 1 1/2.
The Eastman Kodak Company also now supplies what it calls Eastman Bi-Pack Film for color work, consisting of a combination Bi-Pack and an additional Panchromatic Film which are chiefly for use in single mirror one-shot color cameras.
The Bi-Pack itself consists of two films. The one nearest the lens is sensitive to blue light only. It is ex-posed through its support, which is colorless. Its emulsion surface, which is turned away from the light, is coated with a red dye layer which acts as a filter for the second member of the Bi-Pack. This second film is Panchromatic, and serves to record the red rays. It is exposed from its emulsion side, which is placed in contact with the red surface of the first film. The Pan-chromatic film has a deep green anti-halation backing which is decolorized in the course of developing and fixing.
A leaflet describing the use of the film, arrangement of the mirror in such cameras, developing formulas, etc., may be had from the Eastman Kodak Company, Rochester, New York.
In the United States the principal films and plates used by color workers are Cramer, Wratten, Hammer, Defender and Ilford. From each of these manufacturers we have secured details regarding the plates and films best suited for separation work, with their own formulas for developing. These data are given at the end of this chapter.
LENSES,—The selection of a lens is a very important item. The lens should be known to be fully corrected for color. Lenses especially corrected for color separation work are termed apochromats. These will give, with one adjustment of the focus, perfect registration and sharp focus of all the colors.
In two-mirror cameras where the image is split three ways, the manufacturers consider it a necessity to use an apochromatic lens. The use of a lens not fully corrected will necessitate a compromise. Either slight lack of register with perfect focus or slight out of-focus with perfect register will be necessary.
In cameras which make use of the Bipac (Dupac) type film and separate blue record a less highly corrected lens will do, as the important colors red and blue (printers) are made in contact at one plane and a slight difference in the yellow (printer) is scarcely distinguishable. However, with the Tripac type of single mirror cameras where the blue printer and the red printer are made in separate planes, high color correction in the lens is more important. In lenses of longer than 7 1/2" equivalent focal length, greater difficulty will be found in using any but fully corrected lenses. Many manufacturers have free booklets describing their lenses for various purposes, which you may obtain direct or from your dealer.
KINDS OF FILTER AND MOUNTING.—Filters should be those supplied by, or recommended by, the maker of the particular plate or film used. If the filters are placed before or behind the lens, a matched set of B glass will be found satisfactory. The filters should be mounted in a row, so that they can be slid easily across the front of the lens. They must be kept absolutely flat and parallel to the lens. A sliding or rotating holder with three openings should be built for this purpose.
Final adjustment of focus should in all cases be made through one of the matched filter set.
Gelatin filter sets can be used before the lens if kept flat and clean (buckled gelatin filters will not do), but are best when used in a slot between the lens elements. Do not use paste or glue on the gelatin filters, as they will warp the filters. Handle the gelatin filters with care so that no finger marks are left on them. If they become grease-marked, get a new set, as they are useless unless clean and clear.
With repeating backs and one-shot cameras, the filters are usually cemented between two thicknesses of optical glass and are placed next to the plates, that is, in front of them.
GREY WEDGES AND COLOR CHARTS.-Provide yourself with a grey scale (or wedge), or several of them in different sizes, such as 1 by 6, 2 by io, etc., and a color chart or two, preferably those supplied or recommended by the makers of the filters and plateS which you are using. The grey scale is indispensable in determining the density balance of the three plates.
The use of the color chart containing squares of blue-green, magenta and yellow serveS to identify the negatives when developed. If a color chart is not used, be sure to mark each negative either by placing white cards with black letters A, B and C in the subject or by marking the holders and the negatives as you load or unload them, or by use of identification marks on the filters as described below.
REGISTRATION MARKS.—In making separation negatives for the engraver, include in the subject at opposite ends registration marks—black crosses on white squareS or white crosses on black squares, of a size which will record from 1/2" on a 5 by 7 to 1y2" on a 11 by 14 negative. These are valuable to both the color worker and the engraver when registering.
NEGATIVE IDENTIFICATION MARKS.—Where the filters are next to the plate, a narrow strip of black paper glued against one edge of the filter will leave a corresponding clear mark on the negative for identification. The usual system for use by the engraver is one line for the A filter, two for the B, three for the C, and in case a fourth black key plate is made this will have four parallel vertical lines on its edge.
With repeating backs or single-shot cameras, use wherever possible a color corrected lens with a Water-house stop opening into which a filter holder with the proper gelatin filter can be inserted between the elements. Such an arrangement gives clean-cut, sharp separations. If your lens doeS not have such a slot, you can have one put in. This work should be done by a competent lens manufacturer.
LIGHTING.—Lighting for color is very important and differs considerably from black and white. In dealing with this subject, I have enlisted the aid of a number of well-known color workers and will try to incorporate as far as space will permit a few useful rules and suggestions. Several flood lights and one or two spotlights such as are used in black and white will do to start. As you go along you will adapt particular types of light for your work.
Start your color lighting with a soft, even light with ample illumination in the shadows. One worker tells us he gets the dramatic effects of black and white by first lighting as in black and white and then building up the shadow detail with diffused spotlights. With practice you will become able to determine how far you can go in effect-lighting for your subjects.
In working on location where you have to use part daylight and part arc light, be sure to balance the arcs and the daylight. A great deal can be done with rheostat control over your electrical equipment by raising or lowering the voltage. The table below gives an idea of the color value of the various types of lights in their degree of whiteness or suitability for use with daylight:
1. Overloaded arc 1" flame = June sun
2. Normal voltage 1" flame = Average sunlight midday
3. Under voltage 1" flame = Early and late sunlight
4. Photoflood—White to yellow according to age of lamp and voltage
5. Photoflash—Use alone
6. Mazda Bulbs—Overloaded—Whitish yellow
7. Mazda Bulbs—Normal yellow
With the increase of the blue or yellow tint of the light, the factors of the red and blue filters will change, going down on one and up on the other, with the green filter factor remaining about the same. One color worker describes this as a seesaw, the blue and red filters going up and down, with the green filters the center support.
Once the lights are set they should not be disturbed until all three negatives are exposed. Do not mix daylight with Mazda.
Unless one has a means of keeping arc light constant, it is best not to use it for separate exposures or with repeating backs. '
SYNCHRONIZERS FOR FLASH-BULBS.—In order to use a number of flash-bulbs at one time to secure instantaneous exposures with one-shot cameras, it is necessary to use a multi-flash unit in connection with the synchronization of the shutter. These units can be purchased ready-made with outlets arranged to plug in a number of flash-bulbs so that the bulbs will all flash at the same time. The filament of each bulb and each line can be tested by such units before the flash is made.
MAKING THE EXPOSURE.—Place a grey scale when-ever possible at some point in the negative not included in the actual subject. Try to place this where it will not reflect any glare. This is needed, as previously explained, to establish correct filter ratios and color balance. Include a color chart to identify the separation negatives. Use also, when possible, registration marks.
Arrange your lighting with due regard for the requirements already given. A photo-electric type exposure meter is very necessary in color work to determine the normal black-and-white exposure. The exposures in color with each filter are arrived at by multiplying the normal exposure by the filter factor given for each color on the card which comes with the plates used, or the ratio which you have determined by practice to be necessary with given light values in order to get identical density of the grey scale in each step in all three negatives.
One cannot spend time more profitably than to first make several sets of separation negatives of a grey scale with color chart and registration marks to determine proper ratio in exposure, registration and color balance.
Once the grey scales are in balance, you can increase or decrease your exposures in the same ratio, to obtain the proper negative contrast.
Exposure controls density, development controls contrast. Equal density and contrast is the goal to be sought after. Where extra development has to be given one, or possibly two, of the negatives to bring the contrast of each step of grey scale into proportionate density, the general density of negative will be increased, but by giving these negatives the necessary extra printing exposure, balanced prints are obtained.
Grey scales are frequently placed for convenience along the outer edge of the subject. In such cases, while they are useful as a guide to the comparative density and contrast of the three negatives, they may not reproduce in neutral tones (without color) in a properly balanced color print or transparency. This is due to the fact that very often the lighting along such outer edges where the grey scale is placed is not of the same color value as the light on the main part of the subject.
DENSITOMETERS.—Until recently, various densitometers or. instruments for measuring the range of the grey scale of the three separation negatives have been constructed to order or imported. The Eastman Kodak Company is now offering a complete instrument of this sort which will check the reading of grey scales by either reflected or transmitted light.
With a reading of each negative at hand, one may make over separation's or adjust as much as possible any variance in the next step, such as in the bromide prints for Carbro, positives for Wash-Off Relief, Chromatone prints, etc.
A new American densitometer recently offered and now available through the photographic dealer is known as a Garometer, which makes use of photo-electric cells to measure the density balance. This type is for transmission only.
These light-measuring instruments are also used in connection with what is termed "masking," for better rendering of color when printing from separation negatives. By the aid of the densitometer, positives of a determined density are made from the red filter (blue printer negative) which are then bound in contact with the green filter (red printer) and blue filter (yellow printer negative) to enable them to give color rendering which will better fit the various pigment or dye methods of making prints from same. Under the heading of separations from Kodachrome, and also in the chapter on Chromatone, a more detailed description of this method is given. Further details may be had on this method in free booklets obtainable from the Eastman Kodak and Defender Companies, both of Rochester, New York.
FILTER FACTORS.—If a one-shot color camera is used, the variations in the filter factors have been balanced for daylight or tungsten light by the maker in the construction of the camera. If such plates do not balance, you may have the wrong filters for the light or plates you are using. Do not change the filter positions except as advised by the camera maker.
For rapid work with one-shot cameras, many workers use large banks of Photoflash bulbs which enable them to make instantaneous exposures. As many as two hundred flash-bulbs are frequently used for one exposure. Special units for instantaneous flashing of all the bulbs are available.
Negatives should be normal with full detail in the shadows—negatives such as will print well on Azo No. 2 or No. 3, depending on the printing medium you are using. Such a negative will retain all the delicate detail in the shadows without blocking up the high-lights. This can be done by the adjustment of lighting, exposure or developer, or by a combination of all three.
The three plates should be developed all at the same time (with temperature constant) in the dark by tray or tank. Time and temperature method should be used, for to try to judge the plates by even the customary green safelight will probably lead to fog. Plates should be agitated during development.
All plate makerS have their own formulas, which come in the box of plates or are given in their free booklets.
If you have given the proper exposure and development, the grey scales will match in density and contrast in the three negatives. If this is not the case, you must vary the exposure and development until the grey scales are as nearly alike as possible. Equal contrast is the important requirement ; density differences in the negatives can be balanced in the printing.
Loss of one or two of the dark steps in the grey wedge indicates under-exposure. If, on the contrary, you have blocked up one or two highlights steps, you have over-exposed.
Keep to the making of the test negative sets until they are right, before wasting the color printing medium. Do not try to compare the negatives without the use of the grey scale.
Later, when you are more expert, you can judge by the grey and white parts of the subject itself, if it is not feasible to use a grey scale when making the exposure. As a rule it is necessary to develop the blue filter (yellow printer) negative about 25 per cent to 50 per cent longer than the others in order to bring it up to the gamma of the other two. This flatness is due to the fact that the silver emulsion is more opaque to the blue and violet light than to the other colors.
With a good set of separation negatives you are now ready to proceed to the making of the color transparency or paper prints by one of the methods de-scribed in the chapters which follow.
FILM AND PLATE DATA WITH FORMULAS: CRAMER PLATE.—For repeating backs and one-shot cameras where speed is essential, the following arrangement of Cramer plates is generally used:
Behind the red filter for the blue printer use Cramer Spectrum.
Behind the green filter for the red printer use Cramer Sure Shot or InstantaneouS Iso.
The latter is the faster of the two.
For the yellow printer, the blue filter is usually omitted and the exposure made direct on the Cramer Alpha plate. Of the three plates mentioned above, the Spectrum is panchromatic; the Instantaneous Iso is orthochromatic and the Alpha color-blind. Where speed is not needed, three separate exposures can also be made on the Cramer Spectrum (panchromatic) with the usual red, green and blue filters, or as some workers prefer, the Spectrum plate can be used behind the red filter and the Medium Iso (orthochromatic) behind the green filter, and either the Medium Iso behind the blue filter or the Alpha with no filter for the yellow printer.
Wratten filters are recommended. Red, A-25, green, No. 60 and blue, No. 48-C2 constitute the standard tricolor set for use with the Cramer Spectrum plates. The No. 60 green also serves when the Sure Shot Medium or Instantaneous Iso are used for the red printer.
Below we give the filter factors for Cramer plates. Filters mentioned below are regular Wratten filters.
FILTER FACTORS FOR CRAMER PLATES
MEDIUM Iso K2 A B-6o C2-48
Open arc lamp 2 1/2 10 5 1/2
Incandescent 2 7 1/2 14
ISO PROCESS 3 9 6 1/2
Open arc lamp 2 1/2 8 1/2 14 1/2
Develop for five minutes at 65° F.; for less contrast, double the quantity of water.
EASTMAN PLATES AND FILMS.—The Eastman Kodak Company recommends that their panchromatic emulsions be used for each of the three separations through the filters recommended in the chart below. A list of the plates and films recommended are given below with their filter factors.
Filters for use with these are: Wratten—A 25 red, B 58 green and C5 47 blue for sunlight, white flame arcs and incandescent tungsten lamp. (K2 is a yellow filter used by engravers when a fourth printer is required.) The difference in filter factors for the various light sources should be carefully noted. Wratten plates may be obtained on special order with an anti-halation backing.
APPROXIMATE WRATTEN FILTER FACTORS.—While it is necessary to check by experience the exact filter factors under your particular lighting conditions, the following tables will give you the approximate factors for the plates mentioned. We are purposely showing only the factors for the plates mentioned. In each package of plates you will find a filter factor card applying to that particular emulsion. Complete data on Eastman filters will be found in the books "Photography of Colored Objects" and "Wratten Light Filters."
For tank development, dilute with an equal part of water, develop about 10 minutes at 65° F. (18° C.).
For tray development, use without dilution, develop about 5 minutes at 65° F. (18° C.).
With these times and temperatures of development, a gamma of approximately 0.7 is obtained on such materials as Eastman Super Sensitive Panchromatic film and Eastman Portrait Panchromatic film.
By increasing or decreasing the quantity of Kodalk in any developer containing this chemical, it is possible (a) to increase or decrease the contrast. obtained in a given time of development, or (b) to decrease or increase the time of development without affecting the contrast.
DK-50 formula is especially recommended for use with Wratten Hypersensitive plates when it is desired to obtain the greatest advantage of their speed.
E-H BORAX DEVELOPER (KODAK FORMULA D-76)
For Maximum Shadow Detail on Professional Plates
Water (about 125° F.) (52° C.) 96 oz. 3000 ccm
For tank use, develop ten to twenty-five minutes at 65° F. (18° C.) in the fresh developer according to the contrast desired. For tray use, decrease the time about 20 per cent. A faster working developer can be obtained by increasing the quantity of borax. By in-creasing the borax about ten times, from 1i6 grains to two ounces 290 grains per gallon (from eight grams to eighty grams per four liters), the development time will be about one-half that of the regular D-76. If a more active developer is required, substitute Kodalk for borax in the formula, and use up to ten times the quantity indicated. With this concentration the development time will be about one-quarter that required with regular D-76.
With use, the D-76 developer becomes Slightly muddy, due to the formation of a suspension of colloidal silver, and the tank usually becomes coated with a thick deposit of silver. Both of these effects are harmless, however, and may be ignored.
Inasmuch as formula D-76 is one which changes in its activity rather rapidly with age unless constantly replenished, the use of the replenisher solution D-76R is strongly recommended for tank development.
Use the replenisher without dilution and add to the tank to maintain the level of the solution. The life of D-76 is extended 5 to 10 times by the use of this replenisher.
HAMMER PLATES.—At the time of writing (1937), the Hammer Company are not quite ready with a panchromatic plate which they plan to put on the market, but have offered the suggestion that some color workers are satisfactorily using their Red Label plate either without or with a blue filter for the yellow printer and their Supersensitive Ortho plate behind the green filter for the red printer, in conjunction with a pan-chromatic plate behind the red filter for the blue printer.
The Hammer Slow plate is recommended very highly by its maker for making correction masks in color separation work.
Below we give their standard developing formulas and suggest that the reader inquire of his dealer regarding the new Hammer panchromatic plates which are to be ready soon.
To develop, use equal parts of water and developer. Develop for approximately six minutes at 65° F. (18° C.).
For use take one part of this stock solution to one and a half parts of water. Develop from six to eight minutes at 65° F. (18° C.).
ILFORD PANCHROMATIC PLATES.-Ilford panchromatic plates are available for three-color work. Ilford panchromatic plates are single-coated and backed. The manufacturers claim that there is less halation with a single-coated, backed plate than with a double-coated plate. The backing is a special preparation which is dark red or magenta in color, and which entirely disappears during development and fixing, and is not to be confused with the old type messy, black backing.
The Special Rapid Panchromatic plate, having a speed of 400 H. & D., is ideal for subjects requiring a medium amount of contrast, and is especially suit-able for the copying of paintings and subjects lacking in natural contrast.
The Soft Gradation Panchromatic plate, having a speed of 700 H. & D. to daylight, and 2000 H. & D. to incandescent light, is used for subjects with more contrast, or where the subject is illuminated by artificial light, where strong shadows are predominant, and where a soft negative is required.
The Ilford Hypersensitive Panchromatic plate is the fastest of the Ilford panchromatic series, and will give the softest results. It is the best plate for use where the exposure must be cut down to a minimum, as in photographing living models. This plate has a speed of 2500 H. & D. to daylight and 8000 H. & D. to incandescent light.
Cards giving filter factors are enclosed in each box of plates, also recommended developing times, and Ilford formulas.
The Ilford tri-color filters should be used when making separation negatives with Ilford plates, as these filters are spectroscopically correct for the color sensitivity of the emulsion.
More detailed information regarding the working of Ilford plates and three-color photography in general, which may be of interest to the half-tone and continuous tone worker, can be found in the "Ilford Manual of Process Work."
Ilford plates and films may be developed with any of the well-known developing agents in accordance with the formulas adapted for each.
ILFORD METOL—HYDROQUINONE.—This developer is rapid and energetic and gives ample density. It will be found very useful in cases of under-exposure. It keeps almost indefinitely in a well-stoppered bottle.
Dissolve the ingredients in the order given. For use dilute one part with two parts of water.
ILFORD TANK DEVELOPMENT.—ThiS method of development gives negatives of excellent quality and it facilitates the development of a number of negatives at one time.
For use dilute one part with 5 parts of water.
This developer keeps in good condition for a long time in the tank, especially if a floating lid is used. It should be invigorated as required with the addition of some stock solution made up without the potassium bromide.
AMIDOL DEVELOPER.—Amidol is not only a favorite for Carbro bromide prints, but is recommended by many color workers for the development of separation negatives. A suitable formula is given below.
Anhydrous sulphite of soda 3 OZ. 85 g
Separately in ten ounces (285 ccm) of cold water dissolve I/ oz. (42 g) of potassium metabisulphite and add to above.
When ready for use take three ounces (90 ccm) of above stock solution to sixteen ounces (460 ccm) of water. Then dissolve in this working solution 30 to 35 grains (2.3 g) of amidol and it is ready for use. This developer must be thrown away each time after development of one or possibly two sets of plates.
FILMS FOR COLOR SEPARATION WORK.—A great deal of color photography is done with films such as De-fender, Agfa and Eastman, so that we are including a list of film and a factor chart for use with them. The factors for Eastman film will be found on page 20 under Wratten filter factors. Those for Agfa and Defender are given herewith:
AVERAGE DEFENDER FILTER FACTOR CHART.—Filters referred to are the regular Wratten. Cards will be found in each box with factors for that emulsion.
FINE GRAIN EXTRA SPEC. FAST
FILTER Daylight Mazda Daylight Mazda
A-Red 8.9 4.4 9 4.5
AGFA FILM FILTER FACTOR CHART.—Filter factors given below are as noted for both Agfa and Wratten filters and are taken from the latest Agfa Filter Factor Chart dated February, 1937.
Film-developing formulas given by the manufacturers, or some of the many already given under plate headings, will be found suitable for use with films as well as plates.
At the present time (1937) Agfa Ansco are not offering any panchromatic plates in the United States.
TWO-COLOR SEPARATIONS.—There are at present available what are known as Bi-pack and Dupac film combinations consisting of two films which are loaded emulsion face to face in a spring tension holder. The film next to the lens is exposed through the back and is sensitive principally to blue and green. Above the emulsion of this film between it and the back film is a red-orange coating which acts as a filter for the panchromatic film in the rear which records the orange-red in the subject.
These films must be loaded in a pressure holder such as the Finlay to insure good contact. The focusing is done on the ground-glass as usual. The thickness of the film being only a small fraction of an inch (about 6/1000) is not enough to interfere with the focus.
Exposure in artificial light (except strong arcs) is made without a filter over the lens. In strong blue Mazda light, arc or daylight, a light yellow filter of the Wratten K1 or K2 type is used. The exact exposure is only slightly more than that normally given to an orthochromatic film.
With a Weston meter use a direct setting of six for tungsten and eight for daylight. Exposures of 1/25 second at f : 6.3 are possible in strong daylight.
Metol 85 gr. 6 g
Develop both films at one time, leaving the front negative (the one with the orange-colored back) 25 per cent longer to improve balance. Wash and fix in the usual manner.
For more contrast, some workers develop with Eastman D-61a or D-72 developing formulas.
The orange stain left on the back of the front film is removed after fixing and washing with a 1 per cent solution of sodium hydrosulphite. Wash well after this.
Negatives made in this way can be printed by the two-color toning and dyeing methods, or three-color prints may be made from them by making a synthetiC yellow printer negative from the two negatives made in the camera.
THREE-COLOR FROM TWO-COLOR SEPARATION NEGATIvEs.—Three-color prints or transparencies are made by many workers from two-color separations such as the Defender Dupac.
Since the front film gives a red-orange printer and the back film a blue printer, one obviously needs a yellow printer for the three-color effect.
The yellow relief positive, Carbro bromide, Chromatone or whatever method you may use, is made from the red printer or partly from the red and partly from the blue printer, to secure the amount of yellow needed.
WORKING INSTRUCTIONs.—The simplest method is to print once from the blue printer, once from the red and then register the two Dupac negatives carefully together and make a yellow printer from the two.
Exposing the yellow printer film or bromide partly under each negative necessitates an arrangement for retaining the exact registration. This is best done by contact as follows: Use a printing frame with an area four times that of the negative or print to be made. Lay down one negative reversed at the right-hand side of frame and tape along its left edge.
Turn the hinged film left like a book page, which will bring it right side up in the middle of the frame. Now take the next film and register it on top of the first one and tape across the top edge so that it can be lifted out of the way and returned at will to place in register. The bromide or positive film is now hinged by its right side at left side of frame. You can now expose for any length of time to either of the negatives for the yellow printer without losing register.
With the yellow printer, bromide, Belcolor, etc., exposed you proceed in the usual way for that process.
IVES POLYCHROME PROCESS.—Frederick E. Ives, who has given much study to color photography, announced through articles in The Camera magazine in 1932, a method of dyeing and toning by which an approximate three-color print or transparency could be made from two-color separation negatives.
This can be done by various methods. One is to tone a blue glossy, single-weight bromide print with the bath given in the chapter on "Mordanting and Toning" and then to cement by amyl acetate a thin relief dye colored orange-red positive film above the bromide. The cement is applied to the emulsion side of both film and paper, and the print is then placed between blotters and run through a wringer. It is then dried under pressure.
Another method is to make use of gelatin reliefs and the regular dye transfer method, using the patent blue dye bath for one and the orange-red for the other. The formulas for these dyes will be found under "Dyeing of Relief Images."
In making transparencies, one may make use of a blue-toned positive and an orange-red dyed positive or two dyed ones as preferred.