Part 2

The plate should first of all be thoroughly soaked in a solution of the alkali which can be used, and then a few drops of the pyrogallol solution be dropped into the developing cup with an equal number of drops of the restrainer. The alkaline solution is then returned to the cup and again poured into the dish and over the plate. By degrees the required phantom image will make its appearance, and now bromide and pyrogallol are added until it is evidently complete. The plate is then washed in water, a final wash being given in a very weak solution of acetic acid or citric and water. After a final rinse with water the plate is treated with the pyrogallol solution and restrainer in the proportion recommended for the ordinary development of the plate, omitting the alkali. The density will begin to appear, and when it flags, a little alkali is added (a few drops at a time) to the solution. Keep the image fairly feeble at above half the proper printing density, and fix. The plate should then be kept for intensification, preferably by Mr. Chapman Jones's, when a mercury solution is applied, and then a ferrous oxalate to reduce the latter to the metallic state. It will be found if this procedure is adopted, that the negative is built up with a greater range of light gradation than by bringing it out by a one-solution method of development. If one wishes to exercise artistic treatment, then in the preliminary stage more importance can be given to any desired part by applying a camel's hair brush soaked in normal pyrogallol solution with its restrainer. The prominence thus gained will be kept in the subsequent operations. When applying the brush care must be taken that the image blends as it were with the rest of the picture. No abrupt increase of density must be permitted, as if it be, the result will be anything but satisfactory.

The following is an ammonia-pyro developer, with which the writer usually works.

A Ammonia 1 part. Water 9 parts.

(Of course, should the ammonia be taken half strength allowance must be made for the dilution.)

B Potassium bromide 20 grains. Water 1 ounce.

(When travelling it is very convenient to have the bromide weighed out into 20 grain packets.)

P Pyrogallol dry.

S Saturated solution of sulphite of soda.

When the view has strong contrasts and the plate has been exposed for the shadows take of A 30 minims and 2 ounces of water and soak the plate in it as given above. Then add to the cup, of B 2 drams, of S 1 dram, and about quarter grain of P. Pour back the solution of ammonia from the dish, and then apply the mixture till all detail appears, and proceed as indicated above. A saturated solution of potassium carbonate may be substituted for the ammonia solution.

Before closing this chapter it may be of use to the reader to tabulate the number of thicknesses of atmospheres through which light has to travel at different altitudes of the sun at sea level.

Altitude. Atmosphere.

90° 1.000 80° 1.015 70° 1.064 60° 1.155 50° 1.305 40° 1.555 30° 1.995 20° 2.904 15° 3.809 10° 5.571 5° 10.216 4° 12.151 2° 18.882 0° 35.503

If sunlight outside the atmosphere be represented by 1 and say 1/10th be cut off by 1 atmosphere, then after transmission through 2 atmospheres only .81 will reach the spectator, and if through 3 only .729. For any atmosphere the diminution will be 1/10th, that is, it will be .9^_x_ where _x_ is the number of atmospheres.

If we ascend the factor varies, there are less thicknesses of atmosphere to go through and we get the following table.

Photographically Visual Transmission Actinic Light Barometer (Sunlight outside Transmitted in Inches. the Atmospheric (Sunlight outside being 1). the Atmospheric being 1).

30 .853 .639 29 .866 .654 28 .875 .672 27 .884 .689 26 .891 .708 25 .899 .730 24 .908 .746 23 .915 .763 22 .922 .787 21 .928 .800 20 .934 .819 19 .940 .833

This table and the preceding one will enable a calculation to be made as to the exposure to be given. Thus at sea level with a photographic brightness of sun of 639,000 candles when nearly overhead, it will at 5° above the horizon only have a photographic brightness of about 1000. At about 9000 feet high the photographic brightness would when the sun is overhead be about 800,000 candles, and at 5° it would have a value of 350,000, showing the greater penetration through the thinner atmosphere.

_W. de W. Abney, C.B., F.R.S., etc., etc._

Negative Making.

DEVELOPMENT, INTENSIFICATION, REDUCING, Etc.

When a sensitive plate has been properly exposed under ordinary conditions, there is no visible change. The action of light produces what is known as a _latent image_ or _developable image_, and in order to convert this into a visible image with sufficient opacity to be useful for printing purposes, it must be _developed_. In the operation of development, the plate is treated with some solution that will act on the exposed parts of the sensitive film and reduce the silver salts contained therein to metallic silver, in quantity proportional to the amount of light-action, whilst at the same time it produces no appreciable change in those parts of the film on which light has acted the least or not at all, and which correspond to the darkest shadows of the object that has been photographed. The solution used for this purpose is called the _developer_.

DEVELOPERS--GENERAL.

The substances that can be employed as photographic developers are now somewhat numerous, but the most useful for negative making are pyrogallic acid (also known as pyrogallol, or for brevity as pyro.), ortol, metol, and hydroquinone (also known as quinol). Ferrous oxalate is likewise used in special circumstances, but not for general work. An ordinary developer as mixed for use contains:--

1.--One of the above-mentioned substances (pyrogallic acid, ortol, metol, quinol) which is the actual developing constituent, and is known as _the reducer_, but requires the addition of the next constituent before it can work.

2.--An alkali, which may be sodium carbonate, potassium carbonate, caustic soda, caustic potash, or, if pyrogallic acid is used, ammonia. The alkali sets the reducer in action and is called _the accelerator_.

3.--A soluble bromide, which must be potassium bromide except when ammonia is used as the alkali, and then it may be ammonium bromide. The chief use of the bromide is to retard the action of the developer, and in particular to prevent its affecting those parts of the film that have not been acted on by light. For this reason the bromide is called _the restrainer_ or, sometimes, _the retarder_.

4.--A sulphite, the function of which is to prevent the solution from becoming strongly discoloured and consequently staining the film. It also affects the colour of the reduced silver that forms the developed image, this colour being browner, and consequently of higher printing opacity, the lower the proportion of sulphite present. Sodium sulphite and potassium metabisulphite are the most commonly used.

The composition of a developer has to be so arranged that, whilst reasonably rapid in its action, it is not so rapid as to be beyond control, and does not produce "general fog" by acting on those parts of the film that have not been acted on by light.

DEVELOPMENT--GENERAL OPERATIONS AND PHENOMENA.

A developer is usually compounded immediately before use by mixing two or more solutions, and in order to ensure uniform action it is essential that the constituents should be thoroughly mixed before the liquid is applied to the plate. If the measuring or mixing vessel is large enough, this can be done by agitating the liquid; if not, the liquid may be poured once or twice from one vessel to another.

The quantity of developer necessary for a plate of a given size depends in some degree upon the size and character of the dish that is used, and is smallest when the bottom of the dish is quite flat and has no ridges or grooves. It is false economy to use too small a quantity, and it may be taken that for a quarter plate 1-1/2 oz., for a half plate 2-1/2 or 3 oz., and for a whole plate 4 oz. of developer should be used.

Ebonite, xylonite, or papier maché dishes are the best for all operations connected with negative making, since they are not so liable as porcelain or earthenware to break a plate if it is allowed to drop into them.

When applying the developer to the plate it is important to cover the whole surface of the plate rapidly and in such a manner as to avoid the formation of air bubbles, and the best way is to begin to pour on the developer at one corner of the developing dish and whilst pouring somewhat quickly move the vessel rapidly but steadily along the edge of the dish to the other corner. If there should be any froth or air bubbles on the surface of the developer, the last portions should not be poured out of the vessel into the dish, and then the risk of air bubbles forming on the surface of the plate will be lessened.

Sometimes after the developer has been poured on and the plate seems to be uniformly wetted, the liquid will recede from one corner or one edge of the plate and the part thus left uncovered will appear as a patch of lower opacity when the negative is finished. This happens either because the dish is not standing level on the table or because the bottom of the dish is not flat; sometimes it happens because too small a quantity of developer has been used.

After the plate has been covered by the developer the dish should be carefully rocked from time to time, and, for reasons that will be explained presently, the time required for the first appearance of the image and the manner in which the different parts of the image follow one another, should be carefully observed.

If the plate has been correctly exposed, the brightest parts of the image will appear (as black, of course,) in about a minute, more or less, according to the temperature, composition of the developer, and character of the plate, and the other parts will follow steadily in the order of their brightness, after which the image as a whole will continue to gain vigour or opacity up to a certain limit. The essential point is that the principal details in the deepest shadows of the subject shall appear and acquire a distinct printable opacity, before the highest lights become so opaque that the details in them are no longer distinguishable. Whether this condition is realisable or not depends very largely on the exposure that the plate has received.

If the image appears in considerably less than a minute and the different parts follow one another very quickly, the plate has been _over-exposed_, and the degree of over-exposure is indicated by the rapidity with which the image appears. In this connection it ought, however, to be stated that with metol and certain other developers, even when the plate has been correctly exposed, the different parts of the image appear almost simultaneously, though the first appearance may not begin until about a minute after the developer has been applied to the plate. It follows that with these developers it is difficult to recognise over-exposure, but it so happens that they are not suitable developers to use when there is any probability that the plates have been over-exposed. On the other hand, if the image is slow in appearing and the brightest parts of the subject are not followed in due course by the middle tones, the plate has been _under-exposed_, and there is considerable danger that the high-lights may become quite opaque before any details have appeared in the shadows, or even, in extreme cases, in the lower middle tones, that is to say, in those parts that are next in darkness to the shadows.

When it is desired, as it frequently is, to alter the composition of the developer during development, the substance or substances to be added should be put into the measuring or mixing glass, the developer poured out of the dish into the glass, and the well-mixed liquid poured over the plate as before. Any attempt to add substances to the developer whilst it is in contact with the plate will probably result in uneven action.

It should be borne in mind that temperature has an important influence on development, the time required for the first appearance of the image and for the completion of development being, as a rule, less the higher the temperature. Further, if the developing solutions are very cold, it is often almost impossible to obtain sufficient opacity.

Perhaps the most difficult thing in connection with development is to know when to stop the process, that is to say, when the image has acquired sufficient opacity, or "density," as it is often called. After all the required detail has become visible, the plate from time to time is lifted carefully out of the developer, allowed to drain for a moment or two, and then held between the developing lamp and the eye; the opacity of the image, especially in the highest lights and deepest shadows, being carefully scrutinised. The appearance of the image as seen when looking at the back of the plate, is also carefully observed.

For this purpose it is very much better that the light of the developing lamp should pass through transparent glass (ruby or deep orange) so that the flame itself is distinctly visible, instead of through ground glass or a coloured translucent fabric. Further, the flame of the lamp, whether gas or oil, should always be turned up to the same height, for it is clear that if the brightness of the flame used for making the examination is not fairly constant, all sorts of variable results will be obtained. For this reason it is much better to judge the opacity of negatives by artificial light than by daylight, the intensity of the latter being so variable. A paraffin lamp with a circular wick and a deep ruby chimney with a metal cap at the top, answers admirably.

No general rules can be laid down; the appearance of the properly developed image depends on the thickness of the film, the granularity of the silver salt, the presence or absence of silver iodide, and the composition of the emulsion used. Experience only is of value, and the best way to secure uniformly satisfactory results, is to keep as far as possible to one brand of plates. With some plates, for example, very little of the image should appear at the back of the plate, with others the greater part of the image must be distinctly visible there.

Sometimes, especially when using small sizes of plates, it is not easy to tell whether all the necessary detail in the shadows has been brought out, and this is an important matter, for if the small negatives are to be used for making enlarged negatives or prints, or lantern slides, there should be very little clear glass indeed even in the deepest shadows of the subject. As a rule it may be said that when every part of the image is at least gray the maximum possible amount of detail has been brought out. If the greyness begins to spread to the margins of the plate where it has been protected by the rebate of the dark slide, general fog is being produced, and, as a rule, little will be gained, but much may be lost, by continuing the development for any considerable time after this is observed. When development is completed the developer is poured off, the plate is well rinsed under the tap or in two or three changes of water, and is then ready for fixing.

DEVELOPMENT WITH PYRO-AMMONIA.

This method of development has the advantage that the constituents can be kept in concentrated solutions, considerable modifications in the composition of the developer can be made very readily and the negatives obtained are of excellent printing quality. On the other hand it cannot be satisfactorily employed with certain brands of rapid plates, because with them it has a tendency to produce general fog, and with some other plates, especially when they are old, it has a tendency to produce what is known as green fog.

Three solutions are prepared:--

REDUCER.

Pyrogallic acid 1 oz. or 10 parts Potassium metabisulphite[1] 1 oz. or 10 parts Water, to make up to 10 oz. or 100 parts

ACCELERATOR.

Ammonia 1 oz. or 10 parts Water, to make up to 10 oz. or 100 parts

RESTRAINER.

Ammonium bromide 1 oz. or 10 parts Water, to make up to 10 oz. or 100 parts

[1] The metabisulphite is dissolved in about 8 oz. (80 parts) of water with the aid of heat, and the pyrogallic acid is then added. When the liquid has cooled it is made up to 10 oz. (100 parts) by addition of water, the whole being well mixed by shaking.

For each ounce of developer, take 20 minims of reducer, 20 minims of restrainer and 40 minims of accelerator, and make up to 1 oz. with water. With some plates 60 minims of accelerator and 30 minims of restrainer may be used, but any greater proportion of accelerator has considerable tendency to produce general fog. On the other hand the proportion of restrainer can often be increased with advantage since, unless the amount added is very large, its chief effect is to prevent general fog; 30 minims of restrainer to 40 minims of accelerator, or 40 minims of accelerator to 60 minims of restrainer are proportions that can be recommended. Too low a proportion of bromide should be carefully avoided.

It is very important to ascertain, by careful trial with each brand of plates that is to be used, what is the maximum proportion of ammonia that can safely be added, and what proportion of bromide to ammonia is necessary in order to prevent general fog. As a rule, the more rapid the plates the smaller is the quantity of ammonia that can be used with safety.

By far the best plan is to keep development well under control by adding only part of the accelerator at the beginning of development and adding the rest as circumstances require.

For each ounce of developer take 20 minims of pyro solution and make up to the required bulk with water. In another measure mix for each ounce of developer 40 minims of bromide solution and 60 minims of ammonia solution, and regard this as the maximum quantity that can be added with that bulk of developer. Now to the diluted pyro solution add about a quarter or one-third of the ammonia and bromide solution, pour this mixture on the plate and observe what happens.

If the mode of appearance of the image indicates that the plate has been correctly exposed, about half the remaining ammonia and bromide mixture may be added to the developer at once, and the action allowed to continue, with occasional rocking of the dish. If development proceeds satisfactorily and, in particular, if the chief details in the shadows begin to appear before the highest lights have become too opaque, it is not necessary nor advisable to add the last portion of the ammonia and bromide mixture, since the tendency to general fog and green fog is reduced when the proportion of ammonia is kept as low as possible. On the other hand, if the development flags and the appearance of shadow detail is a little tardy, the rest of the ammonia and bromide mixture must be added.

If the plate seems to be over-exposed, no more of the ammonia and bromide mixture should be added for some time, until it is seen whether the quantity already in the developer will suffice to complete development. If it seems that the over-exposure has been considerable, a further quantity of pyro solution (10 to 20 minims per oz.) and also of bromide solution (10, 20, or 30 minims per oz.) may be added with advantage. Development is then allowed to continue and the negative is examined from time to time; if it is seen that the opacity does not increase, or if sufficient detail in the deep shadows does not appear, further small quantities of the ammonia and bromide mixture may be added _cautiously_ until the required result is obtained, waiting a little while to see the result of each small addition before adding more.

When the plate behaves as if under-exposed, dilute the developer at once with half the quantity or an equal quantity of water, according to the degree of under-exposure indicated, and add the whole of the ammonia and bromide mixture. These modifications should check the rate at which the high-lights of the subject gain opacity, whilst accelerating the appearance of the middle tones and shadows. Should this effect not be produced, further quantities of ammonia and bromide mixture may be added or, in extreme cases, ammonia alone, and the developer may be still more diluted with water.

If any considerable parts of the image still show no detail, local development with a brush may be tried as a last resource. A soft camel's hair brush, preferably mounted in quill, is used. Some of the ammonia and bromide mixture is placed in a vessel and diluted with two or three times its volume of water. One corner or edge of the plate is raised so that the part to be treated is lifted out of the developer, the diluted ammonia and bromide mixture is applied rapidly with the brush, and the plate is allowed to drop gently back into the developer. The treatment may be repeated if necessary.

Should all these devices fail, the plate is hopelessly under-exposed.

Sometimes, when working with a diluted developer as just described, it happens that although all the necessary detail has been brought out, the image gains in opacity very slowly. Provided that all the required detail is visible, small quantities of pyro solution may be added in order to gain opacity more quickly.

PYRO-SODA DEVELOPMENT.

When sodium carbonate is used as the alkali in place of ammonia the developer acts somewhat more slowly and is less liable to produce fog, especially with very rapid plates, and there is very little tendency to produce green fog. On the other hand, variations are not so easily made in the composition of the developer. Some people find the absence of the smell of ammonia a decided advantage.

STOCK PYRO SOLUTION.

The same as for Pyro-Ammonia.

DILUTE PYRO SOLUTION.[2] Stock pyro-solution 1 oz. or 10 parts Water 10 oz. or 100 parts

SODA SOLUTION. Sodium carbonate, crystallised. 1 oz. or 10 parts Sodium Sulphite 1 oz. or 10 parts Potassium bromide 10 grains or 0.23 part Water to make up to[3] 10 oz. or 100 parts

[2] No more of the dilute pyro solution should be made up than is likely to be used during the same day, but it will keep well enough for a day or two.