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:
   

Fig 72

Fig 73

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.

Fig. 74. Albumen beaten into Froth.

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.

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:

1- Cleaning
2- Coating with collodion.
3- Sensitising.
4- Washing for a few moments in the first bath of water contained in the gutta-percha vessel.
5- Washing a second time in a bath, where it is left for several minutes.
6- Leaving to drain.
7- Coating with iodised albumen, which has been before used for removing the excess of water.
8- The immediate application of another coating of fresh iodised albumen.
9- Lastly, leaving it to drain and dry.

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

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:\

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.


By van Monckhoven, Désiré van