Tinting and toning of Eastman positive motion picture film — Themes and Context

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Tinting and Toning _of_ Eastman Positive Motion Picture Film

Price $2.50 Second Edition—Revised

Eastman Kodak Company Rochester, N. Y. 1918

Owing to the difficulty of obtaining foreign made dyes, a revision of the first edition of this publication has been made necessary.

As the result of an exhaustive series of tests of the products of the National Aniline & Chemical Company, Incorporated, New York City, it is now possible to recommend a number of American made dyes suitable for the tinting of motion picture film, and those recommended in this book are in most cases equal in every respect to those previously obtained abroad.

To date, it has not been possible to obtain a thoroughly satisfactory blue dye, film tinted with the Cine Blue recommended being too red, especially before drying. A more suitable dye will no doubt be available in due course.

The number of sample tints has been curtailed to twelve, and these are given merely for guidance. It is intended that the various formulas should be altered to suit individual requirements.

The chapter on toning has been thoroughly revised, a number of tones having been eliminated and others substituted. The formula for the copper tone has been improved, while the formulas for green tones requiring the use of vanadium chloride have been eliminated in view of the expense and difficulty of obtaining satisfactory vanadium chloride. With the samples at present on the market it has not been possible to prepare a single-solution toning bath which would keep for any reasonable length of time.

Attention is drawn to the new method of dye toning[1] recently worked out in our Research Laboratory. This consists in first treating the film in the copper toning bath and then immersing the washed film in a solution of a basic dye, the dye attaching itself to the image and leaving the gelatine clear. Although specific directions are given for obtaining five tones only by this method, as further dyes are available, those suitable for toning purposes will be published in due course.

The method of producing sulphide tones has been changed to one of simple re-development with sodium sulphide, the addition of hypo to the sulphide solution having been eliminated. By commencing with thin positive film of the correct density, and using a plain solution of sodium sulphide for re-development, satisfactory transparent tones are obtainable with precision.

The formulas for the iron and uranium tones are the same as in the first edition.

EASTMAN KODAK COMPANY, ROCHESTER, N. Y.

Tinting and Toning of Eastman Positive Motion Picture Film

In the production of motion picture film it is becoming more common to vary the color of the film either by toning or tinting or by a combination of the two processes. Toning consists in either wholly or partially replacing the silver image of the positive film by some colored compound, the clear portions or highlights of the image, consisting of plain gelatine, remaining unaffected and colorless. Tinting, on the other hand, consists of immersing the film in a solution of dye which colors the gelatine itself, causing the whole picture on the screen to have a veil of color over it.

In “tinting” the following factors must be taken into consideration:

Nature of the Dye Employed

Dyes are chemically of two different types, acid and basic; so-called acid dyes are the alkali salts of organic acids, while basic dyes are the chlorides, sulphates, etc., of organic bases.

For the tinting of film only “acid” dyes have been considered since it is not possible to make a complete selection from basic dyes alone, which would necessitate the use of acid and basic dyes in admixture—a procedure highly undesirable and in many cases impossible.

Any dye suitable for admixture with others to produce intermediate tints should possess the following properties:

_A._ The dye should be inert and not attack the gelatine or support. This is of fundamental importance as the gelatine coating of dyed film in many cases has a tendency to lose its flexibility, giving rise to what is known in the trade as “brittleness.”

Several dyes when employed at a concentration of 1% attack gelatine readily at 70 degrees F. and vigorously at 80 degrees F., especially in presence of small amounts of acid, producing a marked softening and often partial dissolution of the film. The effect is roughly proportional to the concentration of the dye and to the temperature, and varies with each individual dye.

Experience has shown that the gelatine coating of film which has been softened in this way by the dye becomes “brittle” on subsequent projection.

The actual factors in the production of brittleness are:

1. The hydrolysing action of acid which in many cases is added to assist dyeing. In case a solid acid is employed the heat encountered during projection will greatly accelerate this hydrolysis.

2. The corrosive action of the dye itself. Dyes vary considerably in this respect according to their particular composition. So far, it has not been possible to make any general classification of dyes in this connection, though nitro compounds appear to be particularly corrosive in their action.

3. The presence of impurities in the dye. These take the form of excessive amounts of loading material such as sodium sulphate or chloride, or small traces of iron, the latter having a tendency to harden the film considerably.

In all the above cases, the physical nature of the gelatine is altered, whereby it loses its property of remaining resilient under normal conditions of temperature and humidity, resulting in “brittleness.”

A suitable test as to whether a dye has any propensity to produce brittleness is to incubate a sample of film, half of which has been dyed, for about 48 hours at 212 degrees F. If any difference in brittleness is noticeable between the dyed and the undyed portions so treated after the film has been allowed to stand in the air for some time, the dye is unsuitable for tinting.

Apart from the above, most dyes when used at a concentration of 1% and at 80 degrees F. produce more or less softening of the gelatine, which may be prevented by:

(a) Use of only dilute solutions. Except in very special cases, a dye solution stronger than 0.5% is seldom required, the usual strength employed being about 0.2%, at which concentration softening is unusual.

(b) Use of a minimum amount of volatile acid in the dye-bath or omission of the same whenever possible.

(c) By working at temperatures not higher than 70 degrees F.

(d) By slight hardening of the film before dyeing and subsequent softening by glycerine, as described below:

_B._ The dye should not “bleed” to any considerable extent when the film is washed; in other words, the rate of removal of the dye should be slow and only a slight amount should wash out in a period of, say, five minutes.

In tinting, bleeding is of very considerable importance, since, during the periods between rinsing after dyeing and the placing of the film on the drying rack, any drops of water on the surface of the film become more or less saturated with dye, and these after drying remain as spots and irregular markings which are very apparent on the screen.

It is possible in some cases to modify this bleeding by an acid “stop bath,” or by adding acid to the dye-bath; though it may be considered a general rule that the bleeding of a dye is a property peculiar to itself. In making a selection of dyes therefore, it is necessary to choose only those whose propensity for bleeding is a minimum.

_C._ The rate of dyeing should be only slightly affected by the addition of acid to the dye-bath, although most acid dyes are more or less sensitive to acid.

In case the rate of dyeing is appreciably affected by the addition of acid it is possible to take advantage of this fact since a much weaker dye solution may be employed to obtain a given tint, while an apparently exhausted bath may be revived by adding a small trace of acid.

Only a volatile acid such as acetic acid should be used since this will evaporate on drying, while the strength of the acid in the dye-bath should not exceed .05% or one part in 2000, otherwise softening of the gelatine is liable to occur, especially if the temperature exceeds 70° F.

In the case of a bath containing a mixture of dyes, owing to the fact that acid affects some dyes more than others, as the dye-bath becomes exhausted and the acid content changes, the tint obtained will gradually change also. It is only possible therefore to use acid with any degree of certainty in the case of dye-baths containing a single dye.

_D._ The dyes should not fade on exposure to heat or light and should not be “dichroic” or change color on dilution.

_Moreover, the wear and tear of the film should not be impaired in any way after dyeing, and even after incubating for 48 hours at 212 degrees F., afterwards allowing the film to humidify, no difference should be discernible between dyed and undyed film so treated._

_E._ The dye should not be affected by the acid fixing bath since any fixing solution accidentally splashed thereon, would destroy the dye immediately.

In view of the large number of tints required in commercial work, it is undesirable to keep a separate dye-powder for the preparation of each particular bath, but rather to prepare the same by admixture of three or more dyes. If three only are employed, mixing must be conducted with great precision in order to reproduce any given tint, but this difficulty is removed by the use of intermediate colors.

The following six standard dyes have been chosen as fulfilling the above conditions as nearly as possible, and by suitably mixing solutions of these, almost any desired tint may be obtained.

Name Used in Formula Commercial Name

Cine Red Serichrome Blue R ” Scarlet Crocein Scarlet MOO ” Orange Orange A Concentrated ” Yellow Niagara Fast Yellow ” Green Ammaco Acid Green L ” Blue Buffalo Fast Blue R

These dyes are obtainable from the National Aniline & Chemical Co., Inc., New York City.

The strength of the dyes may vary slightly from batch to batch, but this variation is usually so small as not to materially affect the nature of the tint obtained from any particular formula.

The Cine Blue dye appears much redder by artificial light than by daylight, especially before drying the film, as do all tints containing Cine Blue.

The following formulas are given merely for guidance and should be altered to suit individual requirements.

When matching any color view only by artificial light.

FORMULAS FOR TINTING AT 65° F.

Tint Number on Chart Avoirdupois Metric Time of Tinting

1. Cine Red 8 ozs. 250 grams Acetic Acid (Glacial) 3½ ozs. 100 grams Water 50 gals. 200 liters 5 minutes

2. Cine Red 8 ozs. 250 grams Water 50 gals. 200 liters 10 minutes

3. Cine Scarlet 8 ozs. 250 grams Acetic Acid (Glacial) 3½ ozs. 100 grams Water 50 gals. 200 liters 5 minutes

4. Cine Orange 8 ozs. 250 grams Acetic Acid (Glacial) 3½ ozs. 100 grams Water 50 gals. 200 liters 4 minutes

5. Cine Orange 1 lb. 500 grams Water 50 gals. 200 liters 10 minutes

6. Cine Yellow 8 ozs. 250 grams Water 50 gals. 200 liters 10 minutes

7. Cine Yellow 4 ozs. 125 grams Cine Green 8 ozs. 250 grams Water 50 gals. 200 liters 10 minutes

8. Cine Green 13 ozs. 400 grams Water 50 gals. 200 liters 10 minutes

9. Cine Green 8 ozs. 250 grams Cine Blue 8 ozs. 250 grams Water 50 gals. 200 liters 10 minutes

10. Cine Blue 8 ozs. 250 grams Water 50 gals. 200 liters 10 minutes

11. Cine Blue 4 ozs. 125 grams Water 50 gals. 200 liters 10 minutes

12. Cine Blue 8 ozs. 250 grams Cine Red 4 ozs. 125 grams Water 50 gals. 200 liters 10 minutes

Dissolve the solid dyes in as small an amount of hot water as possible, and filter through fine muslin. Pour hot water over any residue remaining, which should only be slight, in order to ensure thorough solution of the dye, and dilute the solution in the tank to the required volume at 65 degrees F.

Nature of Positive Film

Only good snappy positive film may be successfully tinted, since tinting tends to reduce contrast.

The depth of the tint obtained depends on the following factors:

Nature and Strength of the Dye-bath

Except in special cases such as fire scenes, sunset and moonlight effects, and the like, it is very undesirable to employ strong tints, since apart from the displeasing effect and irritation to the eye, the dyes produce a slight softening of the gelatine film when used at 80 degrees F. in 1% solution.

Should it be necessary to employ concentrated baths in summer, either cool the dye-bath or use a suitable hardener. This will be unnecessary if hardener is employed in the fixing bath after development, but otherwise if formalin (40%) be added to the dye-bath to the extent of 1 volume to 400 volumes of dye solution, no trouble will be encountered. During the winter months, when it is advisable to treat all film after developing and fixing, with glycerine, the latter may be incorporated with the dye-bath, thereby eliminating an extra operation. The strength of the glycerine should be 2%, or two volumes per one hundred volumes of dye solution. In most cases, however, the addition of glycerine considerably retards the rate of dyeing, so that in order to obtain the same degree of tinting within a period of ten minutes, the concentration of the dye-bath should be increased accordingly.

When delicate tints are employed, the effect is both to remove the contrasty black and white effect, and to add a touch of warmth to the black deposit of silver, even in cases where the highlights are insufficiently stained to be noticeable. The result in many cases is equal to that obtained by partial toning, for example, tint No. 11 gives the effect of a blue-black tone.

Temperature of Dye-bath

Although temperature has little effect on the rate of dyeing with the dyes recommended, when used without the addition of acid it is advisable in all cases to work at 65 to 70 degrees F. in order to produce uniform results and remove any danger of softening the film.

In order to duplicate any particular tint with a given dye-bath the film may be dyed either by time or by inspection. Dyeing by time is reliable if the dye-bath does not contain acid, though if acid is present, in time the acidity decreases, causing a slowing down of the rate of dyeing so that it becomes necessary to judge the progress of dyeing by inspection.

If two or more tints of the same color are required, in order to reduce the number of individual dye-baths to a minimum, it is better to vary the time of dyeing rather than to vary the dilution of the bath, providing the time of dyeing for the lighter tint is not less than one minute, which time is considered a minimum for the production of uniform results and for complete control of the dyeing operations.

The time of dyeing also depends somewhat on the previous handling of the film. Film which has been fixed in a bath containing ordinary, or chrome alum, dyes more quickly than that treated with plain hypo and hardened with formalin.

It is probable therefore, that small traces of alum are left in the film even after prolonged washing, which serve as a mordant for the dye.

The film samples herewith shown were fixed in the regular acid hypo bath, so that if for any reason the tints indicated are not obtained in the time stated, then either the time of dyeing or the dilution of the dye-bath should be altered accordingly.

Should the film for any reason be over-dyed, a small portion of the dye may be removed by washing for 10 to 15 minutes, though the nature of the dyes will permit only slight mistakes to be rectified in this manner.

Life of the Dye-baths

This averages about 40,000 feet per 50 gallons of dye-bath. The baths may be revived at intervals by the addition of more dye, though this procedure is uncertain and it is generally advisable to mix fresh solution.

The addition of a trace of acetic acid (1 part in 1000) will revive an apparently exhausted bath though as stated above, it is only advisable to do this in the case of baths containing a single dye.

Either the “drum” or “rack” method may be employed, and in either case after dyeing for ten minutes (during which time the drum or rack should be agitated to ensure even dyeing and prevent accumulation of air bubbles) the film should be given a thorough rinse in plain water.

Before drying films on racks it is advisable to set the rack at a slight angle for a few minutes, to enable the surplus water to drain off more readily through the perforations. If drums are used for drying it is advisable to remove the surplus water by whirling the drum previous to drying.

If uniform results are to be obtained, film should never be passed through the projector before either tinting or toning.

How to Obtain Intermediate Tints

The twelve tints above are given merely as examples; other tints may be readily obtained by making a trial with a small amount of solution on a short length of film, taking care to match the tint in artificial light and not by daylight, since any dye containing Cine Blue appears redder by artificial light than by daylight.

When matching think of the tint as being made up of one or more of the colors, red, yellow, and blue. Colors such as orange are made by mixing yellow and red, violet by mixing red and blue, and green by mixing yellow and blue. Browns are obtained by mixing all three colors red, yellow, and blue.

When comparing any two particular tints, it is usual to say that one is redder, yellower or bluer than the other, and the two may therefore be matched accordingly.

Almost any tint if delicate may be employed with advantage, though for general use those ranging through pink, rose, orange, yellow, pale green and pale blue are to be recommended; others are for special purposes.

It is always desirable to obtain harmony in color, especially when combining tinting with toning, so that the combination is pleasing to the normal eye.

For local tinting and hand coloring, the above dyes are likewise satisfactory.

Streaks and Uneven Coloring

a. Grease on the film. Never project film before tinting.

b. Slight bleeding and insufficient squeegeeing when on the drying rack. Always carefully remove any surface moisture from the film with a damp chamois, before drying.

Sludge in the Dye-bath

This is due to the precipitation of the dye by small traces of alum or iron in the water supply. In many localities water is purified by adding alum, and only the smallest trace need be present to throw some of the dye out of solution.

Frothing of the Dye-bath

This occurs only when tinting on the drum with Cine Scarlet, Cine Orange, and Cine Green, but no inconvenience will be caused if the drum is revolved slowly.

[1] The patent rights to this method are being secured by us, but it may be freely used for toning motion picture film manufactured by the Eastman Kodak Company.

As distinct from tinting, a toned image consists of a color image embedded within a layer of colorless gelatine, so that while the highlights are clear, the shadows are colored.

The coloring matter may consist of an inorganic colored compound or a dye, or of a mixture of both, and by wholly or partially replacing the black and white silver image by one or more of these substances, a colored image is produced.

It is, of course, important that the colored compound should be as transparent as possible so that the full tone will be apparent on projection. In this respect, while some samples of toned film appear colored in the hand, they produce a substantially black and white image on projection, so that when judging any particular tone, it is absolutely necessary to view the image on the screen.

Of the various inorganic colored compounds, the metallic ferrocyanides are the most suitable for toning purposes of which:

Iron (ferric) ferrocyanide is blue, Copper ferrocyanide is red, and Uranium ferrocyanide is reddish brown.

It is the object in toning to replace the metallic silver composing the image more or less by one of the above compounds or by a mixture of these. In this way intermediate tones are obtained.

Toning may be effected either by a single solution process or a two solution process.

This consists of first converting the silver image into silver ferrocyanide by a suitable bleaching bath, thoroughly washing, and acting upon the ferrocyanide image with a metallic salt, usually in presence of an acid, the metallic ferrocyanide being produced by double decomposition. The reaction, however, is never complete, so that the image is mixed with undecomposed silver ferrocyanide which tends to make the image opaque, but at the same time it also adds “body” to the latter. Providing allowance is made in the original positive for this intensification, good tones are obtained. (See Tone G.)