van Monckhoven, Désiré van. A Popular Treatise on Photography. Translated By W.H. Thornthwaite. London, 1863.
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ONE of the most unfortunate circumstances connected with the practice of photography on wet collodion, is the necessity, in travelling, for the photographer to employ a tent, which adds greatly to his luggage. This inconvenience is due to the fact that the operations of sensitising and developing must quickly follow each other, for, if too long a time elapses between them, the nitrate of silver crystallises on the surface of the glass, and causes an infinite number of small spots to be formed over the entire surface of the picture.
If the glass plate, covered with its sensitised coating of collodion, be washed with distilled water when re. moved from the silver-bath, and left to dry, it loses nearly all its sensibility, and will give but very imperfect pictures.
M. Desprats and M. Dubosq have partially remedied this fault: the former, by adding half per cent. of resin; the latter, some few drops of amber varnish to the collodion; in whichever of the two methods it is prepared, it must be used exactly as ordinary collodion, with the exception that when the glass is removed from the silver-bath, it is to be well. washed and dried in the dark. Plates thus prepared will preserve their sensibility for many days. The time of exposure in the camera ought to be tripled, and the development made with solution of gallic acid.
M. Dupuis recommends the adoption of the following process. Ordinary iodised collodion is employed, and the glass plate after being sensitised, is well washed in distilled water. A solution of dextrine, in ten times its weight of water, is left to settle, and then decanted so as to be free from impurities. A requisite quantity of this solution is poured over the sensitised glass plate, recently washed, and while still moist, in such a manner, that it spreads evenly over its surface; it is then drained and dried.
The plates thus prepared will keep good for several days; but the time of exposure in the camera must be tripled, that is to say, if with wet collodion, 30 seconds of exposure is required, it will be requisite to give 90 with a plate prepared with dextrine.
Before developing the plate, it is washed with pure water. An apparatus, consisting of a flat-bottomed flask, &c., similar to that described page 57, is useful for this purpose. The picture is developed with pyrogallic acid.
A great number of other dry processes have been proposed; but two, above all others, have obtained the preference of the photographic public, as well in England as in France and Germany, these are the collodio albumen process of M. Taupenot, and the tannin process of Major Russel. These two processes will, therefore, be described in all their details.
As by this process a considerable number of plates can be prepared in a few hours, which is very convenient, especially for obtaining stereoscopic positive proofs upon glass, which will presently be described. The following will be found an excellent method, and one which will enable a hundred of these plates to be properly prepared, in two operations of four hours' continuous work, it being understood that the glasses do not exceed the dimensions of 9 inches by 7 inches, and that they are all cleaned beforehand.
In the dark room are arranged two vessels of gutta-percha, one beside the other, both containing a silver-bath composed of--
|Fused Nitrate of Silver||1050 grs.|
One bath only may be employed, but with two the operation, as will be perceived, is much quicker.
Ordinary negative collodion may be used, but it will be found an improvement if the collodion is a little less iodised, such as is obtained by adding to the ordinary collodion--of which the formulae has been given at page 22--one third of its volume of a mixture of about two parts of ether and one of alcohol.
|Collodion, ordinary, (page 22)||3 ounces.|
|Ether, 5 fluid drs.||1 ounce.|
|Alcohol, 3 do.|
For the purpose of facilitating the description, the glass plates will be designated by the letters A, B, C, and the nitrate of silver baths by numbers 1 and 2.
A glass, A, is coated with collodion and plunged into the first silver-bath (No. 1). A second glass is now coated with collodion, and plunged into the second bath (No. 2).
By the side of the silver-baths should be placed a vessel of gutta-percha of considerable depth and filled with filtered rain-water, or better, with distilled water. This bath ought to be as capacious as possible.
When the first glass, A, has been a sufficient time in the silver-bath, No. 1, which is ascertained by the disappearance of the greasy veins which have been spoken of at page 35, it is taken out and placed in the bath of water contained in the vessel of gutta-percha.
A third glass, C, is then coated with collodion and plunged into the silver-bath, No. 1, from which the first glass was taken, and then the glass in the bath of water is removed, and placed in a large wooden tub (Fig. 71) filled with rain-water, and sufficiently large to hold front eight to ten glasses, placed side by side.
Fig. 71. Tub for Washing Plates.
The second glass, B, is now taken from the silver-bath and plunged into the bath of water in the gutta-percha vessel. It is left here while another glass is coated with collodion and sensitised, and when that is finished the second glass, B, is taken from the water, to be placed in that contained in the large vessel Fig. 71. The plate, C, is removed to the bath of water, a fresh plate inserted, and the same series of operations repeated for the number of prepared plates required.
It will be understood that this method of preparation being a continuous one, is necessarily very rapid. When the large vessel of water is filled with plates, they are to be taken out and placed inclined against the wall, resting at the bottom on some bibulous paper, and with their prepared or collodionised surfaces towards the wall, as described at page 67.
If the operation be conducted on a small scale, with one glass at a time, then, when the first plate is taken from the silver-bath and plunged into the water-bath, another plate is coated with collodion and placed in the nitrate-bath, and during the time it has to remain in it, the first plate is removed to a fresh quantity of water contained in a trough of wood or gutta-percha.
Whichever method be employed, the result will be the same, provided that care be taken to remove the whole of the nitrate of silver, which covers the plates, with abundance of water; if the trough be small, the water must be often changed; but if it be of large size, this way be dispensed with.
When the whole of the plates are prepared, some solution of common salt is added to the water contained in the gutta-percha trough.
A white precipitate is formed of chloride of silver, which can be retained until of sufficient quantity, with other residuums, to be reduced into metallic silver by fusion in an earthen crucible with carbonate of soda.
Each glass plate should remain in the water at least ten minutes, and ought to be kept upright, the better to remove all the soluble salt of silver from the texture of the collodion coating.
The glasses, coated with collodion and washed as just described, must be covered while still moist, with iodised albumen, which is thus prepared:
Fresh fowls' eggs are broken across the middle, the whites carefully separated, and then poured into a glazed earthen vessel, to which is added a quantity of iodide of potassium, equal to 7½ grains to the white of each egg employed. Before adding the iodide of potassium to the white of egg, it should be dissolved in an equal weight of water; for example, if ten, twenty, or fifty eggs be used, 75, 150, or 375 grains of iodide of potassium are required dissolved in 75, 150, or 375 grains of water.
The whole is then beaten completely into froth by means of a bundle of twigs, represented at Fig. 72, or of tinned iron wire, mounted in a handle, Fig. 73. This froth is left to itself in a glazed earthen vessel, Fig. 74,
for twelve hours, when the greater portion is resolved into clear albumen, which can be poured off into a wide-mouthed bottle. This iodised albumen is used to pour over the collodionised glasses after they have been taken from the trough, Fig. 71, and drained for one or two minutes on a wooden shelf, Fig. 69.
Fig. 74. Albumen beaten into Froth.
M. Taupenot employed fermented albumen; but it is now not generally used or to be recommended.
Iodised albumen can be preserved for a considerable time during winter, but in summer it is apt to decompose very rapidly. It should be kept in well-closed bottles in a cool place.
During the time that some of the glasses require to remain in the silver-bath, those which have been draining against the wall are to have a small quantity of the albumen poured on each, and allowed to run over every portion of the moist collodion surface; the glass is then held vertically, so as to allow the excess of liquid to flow into a separate bottle, which, for the sake of distinction, will be called B.
A fresh quantity of the iodised albumen is now poured on the glass, and made to flow over every portion of its surface, the excess being received back into the bottle.
The glasses thus albumenised are left to dry, the upper part of each leaning against the wall, and the lower resting on some blotting-paper, as shown at Fig. 69.
The albumenised surface should be towards the wall, to avoid dust.
The reason for giving the plates two coatings of albumen is that the first application serves to remove the water which impregnates the collodion surface and allows the second quantity to give a perfectly uniform coating. The albumen contained in the bottle, B, can be used a considerable number of times for giving the first coating or until it becomes too diluted with the water derived from the plates, when a fresh quantity must be used; whereas, that employed for the second coating, on the contrary, can be used as often as required.
The glasses, when removed from the bath of water, should not be allowed to dry before being albumenised, otherwise the albumen is spread with difficulty on the surface, and stains are subsequently produced.
The albumen should not be applied sparingly to the glass, but at the same time it should not be allowed to flow over to the back of the plate; if this should happen, it is best removed, when perfectly dry, with some bibulous paper moistened with water.
Walking about the room when the albumenised glasses are being left to dry should be avoided as much as possible, so as to prevent any particles of dust, &c., settling on them. In about twelve hours they will be sufficiently dry, when they can be preserved for an indefinite time, if placed in a grooved box to protect them from damp and the direct light of day.
All the foregoing operations are to be done in the dark room, and when finished, the water in the large bath may be thrown away, but that in the smaller bath of gutta-percha should be retained, for the purpose of precipitating the silver it contains, as before described.
The following is a resumé of the first series of operations, in their proper order, that each glass undergoes:
On the evening, or at most the day before requiring to use the plates for taking views, they must be submitted to a second series of operations, so as to render the iodised albumen surface sensitive to light.
A great number of albumenised glasses may by prepared at a time, because they can be kept for an indefinite period; whereas, no greater number of them should be sensitised than will be used in a very short time, as they then rapidly deteriorate by keeping.
For sensitising the glasses a bath of aceto-nitrate of silver is required, composed of
|Distilled Water||16 ounces|
|Glacial Acetic Acid||1 ounces|
|Fused Nitrate of Silver||1½ ounces|
This bath requires to be filtered before being used, and a gutta-percha dish should be employed for it. After being used for a few weeks it becomes of a yellowish tint, that can, however, be removed by being shaken up with some kaolin. As a matter of precaution the kaolin may always remain at the bottom of the bottle, and the liquid decanted from it when used.
At the side of the bath of aceto-nitrate of silver should be placed another of much larger size, filled with filtered rain-water.
An albumenised glass is immersed with one quick movement into the aceto-nitrate of silver, and left there for fifteen seconds or more, it is then placed in the bath of rain-water, which is shaken a short time so as to remove the excess of nitrate of silver. This being done, it is taken out of the water and left to dry against the wall in the manner previously described. It is almost needless to say that the operation of sensitising must be done in the dark room with a yellow light. The glasses thus sensitised, when dry, are ready to receive the impression in the camera, after which they can be kept for a fortnight before being developed, although, as a rule, the shorter time that elapses between the sensitising and development the better will be the result. To obtain good proofs, not more than three days should intervene between the two operations. In summer especially, the time should be as short as possible; in winter it may be longer without so much risk of injury.
The sensitised glasses ought to be preserved in grooved boxes free from chinks or cracks through which the daylight might pass, and kept as dry as possible.
When required for use they are placed in the ordinary collodion frame for views. There are, however, some frames particularly devised for dry plates, which hold two glasses and have two slides, first one of the glasses is exposed to the light, and then the other, by simply turning round the frame.
The time of exposure for a collodio-albumenised plate is fully double or treble that required for ordinary collodion. Experience alone will guide the operator in this particular.
As the pictures are generally developed after returning from an excursion, it is an excellent plan, to ensure a good proof of any particular view, building, &c., to take two impressions, but with different times of exposure.
The collodio-albumen process is also particularly well adapted for obtaining transparent positives on glass. For this purpose the sensitised surface of the prepared plate is put in contact with the varnished surface of the negative, and placed in a close frame similar to that used for exposing the plate in the camera. By opening the sliding shutter the diffused light of day is allowed to act for three or four seconds, taking care that in arranging the glasses in the frame, the light passes through the negative before striking the sensitised plate. The plate is then taken into the dark room, and developed in the ordinary manner.
When this process is followed the positive picture obtained has a very good effect if placed before a window; it should be mounted with a plate of ground glass, the albumenised surface of one in contact with the ground surface of the other, and the two plates united by a border of black paper pasted round the edges.
The following is the method of developing the collodio-albumen plates:--
Place in a porcelain capsule 15 grains of gallic acid, and pour over it 3¼ ounces of hot distilled water, and mix them well with a glass rod; when the gallic acid is dissolved, or nearly so, add 13 ounces of cold water, and filter the whole into a bottle for use.
This liquid is poured into a porcelain dish to about the depth of an inch and to each quantity of three ounces employed is to be added one-fourth of a drachm of the following solution:
|Distilled Water||35 ounces.|
|Fused Nitrate of Silver||230 grains.|
|Glacial Acetic Acid||9 minims.|
And care should he taken that the whole be thoroughly mingled together, otherwise stains will be formed on the surface of the negative.
The exposed albumenised plate is to be quickly plunged into this liquid, the coated surface upwards, and raised up and down for several times by means of a hook so that the fluid flows well over its surface. It is necessary that the porcelain dish should be adapted for the purpose and with a flat bottom so that the glass may be perfectly immersed in the solution.
At the end of the first hour or two the sky and other parts highly illuminated will hardly have made their appearance, but in the succeeding two hours the proof usually comes out with extreme vigour. It is always well to watch this operation so as to stop it so soon as the development is complete, which, however, sometimes takes as lout; as twelve hours. The colder the weather the longer the time required. In winter it is preferable and sometimes necessary, to develop in a warmed apartment.
Very often in about three or four hours the development of the image can be accelerated by renewing the gallic acid and doubling the dose of nitrate of silver, that is to say, to each 3 ounces of solution of gallic acid add a half' instead of a quarter drachm of the aceto-nitrate of silver; but if this is done the dish must be kept agitated, otherwise the particles of reduced silver which are formed would attach themselves to the picture and entirely spoil it.
To succeed well, two conditions are indispensable-a warm room, about 68° Fahr., and a slow development. It is also very important that the gallic acid should not be allowed to become coloured and muddy; if this should happen, the glass must be washed, so as to remove the thick and decomposed gallic acid from its surface, and placed in another dish with some fresh solution of gallic acid, to which has been added a less quantity of aceto-nitrate of silver than was employed at first.
This last observation is most important, and the operation is one that cannot be too often repeated; with a proper attention to the time of exposure and consequent regulation of the doses of gallic acid, the picture should be well and perfectly developed in about four hours.
To finish off the proof, it is washed with water when taken from the gallic acid bath, and fixed with hyposulphite of soda in the manner described for the ordinary wet process-a final washing completes the picture. It is useless to varnish the plate, as the albumen itself forms an excellent preservative coating.
As the beauty of a collodio-albumen proof greatly depends upon the proper time of exposure in the camera, it may be useful to give some of the indications of a too short or too lengthened action of light.
If the exposure has been too short, the picture does not come out well even after twelve hours of development and repeated changing of the gallic acid solution, the sky alone is distinctly marked, all the other parts of the proof have a general grey tint, without the least vigour. Nothing can remedy this fault. If, on the contrary, the exposure has been too long, the sky shows itself very quickly, as well as the other light parts of the picture. In about an hour the proof exhibits a considerable amount of intensity in all its details. If the development be now stopped, a passable picture may be obtained; but if it be continued, the whole of the image becomes grey, and the sky, although apparently very dark, because viewed by reflection from a white ground, is, nevertheless; also grey. Overexposure is likewise indicated by a red tint, which the proof takes after being fixed.
When the time of exposure has been correct, the sky begins to show itself in about an hour, and very gradually increases in intensity, and becomes of an absolute black, even when viewed as a transparency after fixing. The whole of the details are shown with great vigour, while the shadows are perfectly transparent.
If the sky should not be sufficiently dark, and it is not possible to take another proof, recourse may be had to stopping out with a little Indian ink mixed with honey and water, and a soft camel's hair pencil. It is, however, next to impossible to do this operation in such a manner that some of the details on the horizon are not injured.
This dry process derives its name from the use of tannin-a bitter principle obtained from gall-nuts a preservative agent. To Major Russell is due the credit of having introduced it.
The glass to be prepared should be cleaned with great care, particularly from any greasy substances. This is conveniently done with a mixture of Tripoli powder, spirits of wine, and solution of ammonia. A tuft of cotton is dipped into this mixture and rubbed over its surface for a minute or so; then well rinsed in water and rubbed dry with a clean cloth.
The glass, just before being used, should be wiped with a perfectly dry and warm cloth, and then coated with the following solution:--
|Nelson's Patent Gelatine||20 grains.|
|Distilled Water||10 ounces.|
Dissolve and filter; this solution will keep good for a considerable time.
This gelatine solution is applied to the glass in the same way as ordinary collodion, taking care that the whole of the surface is covered, and that the back of the plate be net soiled. The superfluous liquid is received back into the bottle, and the plate set to dry, as shown at Fig. 69; when well drained, remove the accumulation of fluid very carefully from the lower edge of the plate by a piece of
blotting-paper drawn along it. When the surface is dry, warm gently by the fire, and retain for use in a grooved box. As plates thus coated will keep good any length of time, any required number may be prepared, taking care that the backs of them are quite free from stains of gelatine.
The gelatinised glass is now coated with old iodised collodion in the usual manner, taking particular care that the whole surface of the plate be covered; it is then immersed in the silver-bath employed for the wet collodion process (page 34), and allowed to remain in it from three to five minutes.
Remove the sensitive plate from the bath, and wash it freely under a water-tap for about a minute, it will then be ready to receive the preservative solution, composed as follows:
|Distilled Water||4 ounces.|
Filter through paper, and measure out two separate portions according to the size of the plate to be prepared, allowing about two drachms in each quantity for a stereoscopic plate. The first portion of tannin solution is poured over the washed coating of the sensitised plate two or three times, so as to remove the water adherent to it, then the other quantity is poured on and off, and the plate placed on end on a piece of blotting-paper, and allowed to dry in a perfectly dark and warm place.
After exposure in the camera, which averages from one to three minutes on a favourable day, and from four to eight minutes in dull weather, the picture is to be developed, for which purpose the following solutions are required:--
|No. 1.||Pyrogallic Acid||72 grains.|
Dissolve and keep in a stoppered bottle.
|No. 2.||Nitrate of Silver||20 grains.|
|Citric Acid||20 grains.|
|Distilled Water||1 ounce.|
Dissolve and filter should any white or other precipitate be formed. To three ounces of distilled water add half a drachm of No. 1, and if the plate to be developed
be a stereoscopic size, take three drachms of this solution and add to it from ten to twenty minims of No. 2; this forms the developing fluid.
The exposed plate is first moistened with distilled water, which must be done quickly and evenly, otherwise stains are produced, and then the developing fluid poured over its surface and kept slightly in motion. The development must be carefully watched, and if' in a short time the sky comes out strongly, but, is not followed by the other details of the object, the plate was not long enough exposed, and the developing fluid must be poured back into the measure, and say ten minims of No. 1 added, so as to increase the quantity of pyrogallic acid. If the whole of the picture, however, appears to come out at once, a few drops of No. 2 is to be added, so as to increase the density of the sky.
When the picture is properly developed, it is fixed with a solution of hyposulphite of soda, washed and varnished as described for the wet collodion process.