PhotoHistory

From: THE BARNET BOOK OF PHOTOGRAPHY

Negative Making
DEVELOPMENT, INTENSIFICATION, REDUCING, Etc.

By: C. H. Bothamly, 1898

DEFECTS IN NEGATIVES

A perfect negative presupposes a perfect plate, correct exposure, and correct development stopped at exactly the right time. It is almost unnecessary to say that all these conditions are rarely satisfied, and consequently most negatives fall more or less short of perfection. The defects may be broadly grouped under two heads, namely, those due to imperfections existing in the film before exposure, and those due to defects or errors in the way in which the plate has been treated. It will be more convenient to deal with the latter, and larger, group first, but there is really no hard and fast division between them.

THE NEGATIVE is THIN, or in other words, whilst showing good gradation, and sufficient relative contrast between the different parts, is as a whole lacking in opacity or printing strength, and gives prints that are deficient in vigor and contrasts. The plate has been removed from the developer too soon, and the remedy is to intensify the image. Sometimes the want of opacity is due to the fact that the developer was too cold.

THE NEGATIVE is TOO DENSE OR OPAQUE and consequently although showing good contrasts and gradations, takes a long time to print, especially on dull days. The developer has been too energetic, or development has been continued too long; the remedy is to reduce the image.

THE IMAGE is “FLAT,” or shows comparatively little contrast between the highest lights and the deepest shadows. This may, of course, be due to the absence of contrasts in the subject photographed; it is commonly due to over-exposure; it may be caused by using a developer containing too little reducer, or restrainer, or both, and too much alkali; sometimes it arises from a defect in the quality of the emulsion, or from the fact that the plate has been coated with an abnormally thin film of emulsion.

THE IMAGE is “HARD,” or shows excessive contrasts between lights and shadows, and is defective in the range of its half-tones. This is probably due to under-exposure, but may have been aggravated by the use of a developer containing too much bromide or too little alkali. Local reduction may partially remedy the defect.

FOG. A more or less marked gray deposit of reduced silver extends over the whole surface of the image. It may be due to over-exposure, in which case the edges of the plate that have been protected by the rebate of the dark slide usually remain clear. It may also be caused by using a developer containing too much alkali, or too little restrainer, or both, or by the plate having been exposed to actinic light outside the camera, including the light from the dark-room lamp if the glass or colored fabric used as the screening material is not efficient. In any of these cases the defect would be observable up to the extreme edges of the film.

The character of the dark-room light should be tested by exposing one half of a plate to it at a distance of say nine or twelve inches for five or ten minutes, the other half of the plate being protected by some opaque substance. The best plan is to put the plate into a dark slide and draw out the shutter half-way. After exposure the plate is treated with a developer in the usual manner, and it can then be seen whether or not the light has exerted any action on the plate.

Slight general fog may as a rule be neglected, but if the amount of fog is at all considerable the plate should be treated with a reducer, and afterwards the image can, if necessary, be intensified.

GREEN FOG. The surface of the film shows a peculiar brilliant green or yellowish-green lustrous appearance, generally in patches, when examined by reflected light, but is more or less distinctly pink when the plate is looked through. This effect is rarely observed except when pyro-ammonia has been used as the developer, and it most frequently occurs with old plates, especially if development has been long continued or has been forced by the addition of comparatively large quantities of ammonia.

If the green fog is only slight it does not affect the prints made from the negative, but in bad cases the prints have a patchy appearance and are less deeply printed at those points where the green fog is worst. Two methods are available for the removal of green fog.

In one of these the plate, after being fixed and washed, is placed in a hypo solution of half the strength of the ordinary fixing bath, and to this hypo solution is added a very small quantity of a solution of potassium ferricyanide, and the mixture is allowed to act on the plate for some time, the dish being rocked occasionally. The green fog will gradually disappear and some more of the ferricyanide may be added, if necessary, to secure this end, but it is important to keep the proportion of ferricyanide as low as possible, otherwise the image itself will be reduced. For this reason, if it is seen or suspected that the green fog is likely to be bad, development should be carried a little farther than usual in order to allow for the slight reduction that accompanies the removal of the green fog.

The other plan is to immerse the plate in a dilute solution of ferric chloride (perchloride of iron) until the green fog has been completely bleached, then wash, first in a dilute solution of oxalic acid and afterwards in water, and finally treat with a developer, preferably ferrous oxalate. The green fog is converted into a very fine grey deposit which is almost invisible and has no appreciable effect on the printing qualities of the negative.

BLACK SPOTS may be due to particles of dirt that have been allowed to lodge on the film during one or other of the operations, or during drying. They may also be due to particles in the emulsion, and in the latter case are generally round and sharply defined.

BLACK MARKS of the nature of irregular streaks, looking, so to speak, like black scratches, are generally due to mechanical abrasion of the film. Pressure produces a developable image similar to that produced by the action of light.

BLACK BANDS, indistinct or nebulous at the edges, are sometimes caused during the coating of the plate with the emulsion, in which case they, as a rule, extend all the way along or across the plate. More commonly they are due to defects in the hinges of the dark slides, which may produce the bands either by allowing light to pass through, or by giving off exhalations that affect the plates if they are allowed to remain in the dark slide for a long time. If the bands are due to the hinges, they will, of course, correspond with them in position, and if the hinge is double, in the distance between them.

TRANSPARENT BANDS, or bands showing less opacity than the rest of the image, are sometimes caused by exhalations from the material forming the hinges of the dark slides.

TRANSPARENT SPOTS if small (”pinholes”), are generally due to the presence of particles of dust on the surface of the plate when it was exposed. Prevention lies, of course, in carefully dusting the plate and the dark slide with a soft, clean, dry camel’s hair brush, before putting the former into the latter. If the spots are larger and circular, they are due either to the formation of air bubbles on the surface of the plate during development, or to the presence in the film of insensitive particles.

UNEVEN OPACITY OR DENSITY, varying gradually from one end or side of the plate to the opposite end or side, is due to uneven coating of the plate. If there is a distinctly defined patch, less opaque than the rest, the plate was not properly covered by the developing solution.

STAINS. A uniform stain, of a yellowish or brown color, is produced when the pyro developer contains too small a proportion of sulphite or is allowed to act for a very long time. Such a stain is rarely observed with the other developers mentioned above. The pyro stain can be more or less completely removed by immersing the plate for some time, with repeated rocking, in the alum solution given above, 1 drachm of sulphuric acid being added to every 10 ounces. The plate must afterwards be well washed in soft water. Similar stains in patches may be caused by using dirty dishes or a developer that has become turbid by being frequently used.

DEEP YELLOW-ORANGE OR BROWN STAINS, appearing gradually in patches or all over the negative, some time after it has been fixed, and washed, and dried, are due either to imperfect fixing or to incomplete washing after fixing. There is no practicable remedy.

HALATION. When the subject photographed includes some part much more brightly lighted than the rest, such as a window in an interior subject, the details of the bright part are not only lost, but the image of it seems to spread in all directions, obliterating the details of the surrounding portions. The effect is especially noticeable when the subject includes dark parts which necessitate a somewhat long exposure. A window at the end of a long dimly lighted interior, or dark trees against a bright sky are cases in point. The effect is really due to the fact that the sensitive film is not perfectly opaque, and some of the incident light passes through the film and is reflected from the back surface of the glass on to the under side of the film, producing a blurred image superposed, as it were, on the normal image formed at the surface of the film by the action of the direct light. The effect is known as “halation.” It is prevented by having a perfectly opaque film, which is a condition difficult to realize in practice, and which, moreover, introduces certain other disadvantages. It is also prevented by coating the back of the plate with some substance that will absorb the rays that have passed through the film, and so prevent their being reflected back against the under side of the film. The substance used must either be opaque or must have a deep orange, brown, or red color, and it must have the same refractive index as the glass, otherwise the reflection will not be prevented. For practical convenience it must also be easily applied and easily removed. Many substances have been recommended but nothing is so good as caramel, prepared by the action of heat on sugar. In order to get the mixture to dry completely after it has been applied, a somewhat troublesome process of purification is necessary, but caramel specially prepared for the purpose can now be obtained from dealers in photographic materials. The caramel (which is a solid substance) is dissolved in just enough water to make a thick syrup, which is carefully applied to the back of the plates in a thin layer by means of a flat brush.

If the caramel does not dry properly the solution may be thoroughly mixed with about one quarter (or more) of its weight of very finely powdered burnt sienna or burnt umber, “ground in water.”

After being coated, the plates require some time to dry, and must, of course, be carefully protected from light. If the dark-room is thoroughly dark, the plates may be put up to dry in the same manner as negatives, but if the dark-room is not suitable, some sort of drying box must be used.

After exposure and before development the backing is removed with a damp sponge; if caramel only is used in a form completely soluble in water, it need not be removed unless a developer is being used that is to be applied to several plates in succession.

REDUCTION

When a negative is too opaque or dense it must be reduced by dissolving away part of the silver that forms the image. The same process is also applied for the removal of general fog, sometimes with a view to subsequent intensification.

The simplest solution to use for this purpose is known as the Howard Farmer reducer and is a solution of hypo mixed with a small quantity of potassium ferricyanide (red prussiate of potash).

FERRICYANIDE SOLUTION
Potassium ferricyanide 1 oz. or 10 parts
Water to make up 10 oz. or 100 parts
This solution must be protected from light if it is to be kept for any length of time.

The negative which, if it has been previously dried, must be soaked in water for some time until it is thoroughly and uniformly wetted, is placed in some fresh hypo solution (the ordinary fixing-bath solution diluted with an equal volume of water) to which a small quantity of the ferricyanide solution has been added, and the dish is rocked repeatedly to ensure uniform action. The rapidity of the reducing action depends on the proportion of ferricyanide solution added, and it is very important not to add too much, otherwise the process gets out of control and reduction goes too far. The image should be carefully watched and the plate removed from the solution and rapidly washed before the apparent reduction is quite as great as it is intended to be. It is much better to stop too soon than too late, because if it is found that a little further reduction is necessary, the plate can be again immersed in the hypo and ferricyanide.

The ferricyanide reducer can be applied locally for reducing high-lights, halated windows, etc., and this is often very valuable, especially in the case of underexposed negatives. A small quantity of hypo and ferricyanide solution is mixed in a measuring glass or some other suitable vessel. The plate is immersed in plain hypo solution in a white dish for a short time and is then raised by one corner or one edge until the part to be reduced is above the solution. The mixture of hypo and ferricyanide is carefully applied with a camel’s hair brush to the parts that are too opaque, and after a few moments the plate is allowed to slip back into the hypo solution and the dish is rocked. If the reduction is not sufficient, the same proceeding is gone through as often as necessary. The reducer should not be allowed to act too long before putting the plate back into the hypo, otherwise the reduction may spread further than is desired. Further, the reducer must not be too strong (i.e., contain too much ferricyanide), otherwise it will produce brownish stains and the action may be too energetic.

The other reducer is known as Belitzski’s reducer, and is made up as follows:

Ferric potassium oxalate 1 oz. or 5 parts *
Sodium sulphite 1 oz. or 4 parts
Oxalic acid 1/4 oz. or 1 part
Hypo solution (25 in 100) 5 oz. or 25 parts
Water 20 oz. or 100 parts
* The formula in “parts” does not strictly correspond with that in ounces, but the difference is immaterial.

The constituents must be dissolved in water in the order given. The solution can be used at once and it keeps fairly well if protected from light, in well corked bottles filled up to the neck.

INTENSIFICATION

Intensification is a process in which the opacity of the image is increased by adding some fresh matter, metallic or otherwise, to the reduced silver that constitutes the developed image.

The usual plan is to bleach the image by means of a solution of mercuric chloride (mercury perchloride or corrosive sublimate), which converts the dark-colored silver into a white mixture of silver chloride and mercurous chloride, and this is subsequently treated with some re-agent which will reconvert the image into a dark product of greater opacity than the original.

It is absolutely essential to successful intensification that the negative be completely fixed and completely washed after fixing, for any trace of hypo left in the film will give rise to brown stains. It is also important, in order to prevent stains of another sort and to secure uniform action, that the mercuric chloride solution be mixed with a small quantity of hydrochloric acid. Too much acid will cause frilling. If the negative has been dried it must be immersed in water for, as a rule, not less than half-an-hour, in order that it may be thoroughly and uniformly wetted.

MERCURIC CHLORIDE SOLUTION
Mercuric chloride 1 oz. or 5 parts
Hydrochloric acid 1-1/2 drachms or 1 part
Water to make up to 20 oz. or 100 parts
When uniform intensification is required the negative is allowed to remain in this solution until it is completely bleached. If, however, it is desired to intensify the shadows more than the high-lights, the plate should be removed from the solution as soon as the shadows have bleached, and should be rapidly washed in order to stop the action on the more opaque parts of the image.

In either case the negative must be thoroughly washed after bleaching, and the water used must be soft water. Hard water tends to produce a precipitate of the mercury salt in the film, which may subsequently lead to stain or fog.

Perhaps the best plan of all, when constant results are desired, is to treat the bleached negative with the ferrous oxalate developer, which will gradually convert the white image into a black one, after which the plate is thoroughly washed and dried. It is recommended that the first water used for washing should be slightly acidified with oxalic acid.

Instead of using ferrous oxalate the bleached plate may be treated with a weak solution of ortol or metol to which some sodium carbonate (soda crystals) solution has been added, but no sulphite. After the image has blackened completely the plate is washed.

With any of these methods if the first intensification is not sufficient, the plate may be again bleached with the mercury solution and the process repeated.

An old method, frequently used, is to treat the bleached plate with dilute ammonia, which converts the white image into a dark brown one of very considerable printing opacity. The results are often very good, but are somewhat uncertain, since the precise effect obtained depends on the strength of the ammonia solution and the time during which it is allowed to act. With somewhat strong ammonia, allowed to act for a fairly long time, part of the intensification first produced is removed. This affects the shadows more strongly than the lights and the result is to increase the contrast of the negative, which is very useful for certain purposes.

The negatives intensified with mercury solution followed by ammonia are more liable to spontaneous change and deterioration than those intensified with mercury solution followed by one of the developers. The latter, in fact, if properly washed, may safely be regarded as permanent.

URANIUM INTENSIFIER

A very considerable degree of intensification can be obtained by the use of the uranium intensifier, which is very different in its mode of action, and is a little uncertain in its results. A solution containing potassium ferricyanide and a uranium salt, generally the nitrate, is applied to the negative, and a deposit of a deep orange-red color is formed upon the silver image and very greatly increases its printing opacity. The great difficulty is to prevent this deposit forming on the whole of the film, and it is absolutely necessary that every trace of hypo should be washed out of the film. The addition of acetic acid to the solution not only promotes uniformity of action, but also helps to keep the shadows of the image clear.

FERRICYANIDE SOLUTION
The same as for the ferricyanide reducer.

URANIUM SOLUTION
Uranium nitrate 1 oz. or 10 parts
Water to make up to 10 oz. or 100 parts

THE INTENSIFIER
Uranium solution (1:10) 1 drachm or 5 parts
Ferricyanide solution (1:10) 1 drachm or 5 parts
Acetic acid (glacial) 2 drachms or 10 parts
Water to make up to 2-1/2 oz. or 100 parts

The negative is placed in this solution and allowed to remain with occasional rocking until the degree of intensification is sufficient, which can only be learnt by experience. If it is seen that the deposit is beginning to form on the clear parts of the negative, the plate should be at once removed. After intensification the plates are well washed. If the water is “hard” the intensification will be slightly reduced during washing, and this is often useful in removing a slight stain over the whole of the plate. Treatment with water containing a small quantity of ammonia or sodium carbonate removes the whole of the deposit, but leaves the original image slightly reduced and also partially altered in composition.

VARNISHING

A negative after being thoroughly dried may be used for printing without any further treatment, especially if only a few prints are required and the ordinary ready sensitized papers or emulsion papers are used. It is, however, better to protect the negative from mechanical as well as chemical injury by means of a film of hard varnish or collodion.

Many excellent negative varnishes can now be purchased, and the general mode of application is the same. The negative must be thoroughly dry, and in order to secure this and to make the varnish flow more easily, the negative is very carefully heated in front of a fire or over a small stove until it is just warm, but not hot. The negative is best supported by means of a pneumatic holder held in the left hand, and a fairly large pool of varnish (the exact amount can only be learnt by experience) is poured on the plate somewhat towards the right-hand top corner, and by carefully tilting the plate it is made to run first to the nearest corner, then along the edge to the further left-hand corner down to the nearer left-hand corner, and back to the right-hand bottom corner, from which it is poured into a bottle. The plate is gently rocked whilst it drains into the bottle, and as soon as the varnish ceases to drop the plate is again carefully warmed until the back of it is just too hot for the back of the hand to bear, after which it is placed in a rack to cool.

It is necessary that the varnish should be quite clear and free from any solid particles, and if necessary it must be filtered through a plug of cotton wool moistened with alcohol and placed in the apex of a glass funnel which is resting in the neck of a clean and dry bottle. Since dust may fall into the varnish whilst it is on the negative, it is the best plan to pour the excess of varnish off the negative into a second bottle instead of back into the first, out of which it was poured. To put it in another way, one bottle should be kept for the clear varnish, and a second bottle for the varnish poured off the plate. When the second bottle is full, its contents are filtered into the first bottle for use again.

Instead of varnish, a film of collodion, toughened by the addition of a few drops of castor oil, and known as “leather” collodion, may be used. The collodion is applied to the plate in the same way as varnish except that the plate is not warmed.