van Monckhoven, Désiré van. A Popular Treatise on Photography. Translated By W.H. Thornthwaite. London, 1863.
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IT has been before stated that when the image is sufficiently developed, the plate should be washed with water, so that the pyrogallic acid may be well removed. Should the film show any tendency to detach itself, this operation must be performed with considerable care. The small shutters may now be opened, so as to uncover the whole of the yellow windows. The light in the dark room is thus, increased, although it still retains its yellow tint.
The result thus obtained is a negative image, but still partly obscured with iodide of silver, which is now to be removed. For this purpose it must be plunged into a bath composed as follows:--
|Hyposulphite of Soda||8 ounces.|
In about half a minute, if the bath is fresh, and some few minutes if' the bath has been much used, all the yellow coating of iodide of silver is dissolved, and there remains on the collodion film only the pure silver compound constituting the photographic image.
Hyposulphite of soda is a crystallised substance, very soluble in water, and can be purchased at a very cheap price.
The solution of hyposulphite of soda may be contained in a vessel of zinc or gutta-percha. It does not stain the hands; on the contrary, it will remove recent stains of nitrate of silver.
Great care should be taken that the vessel containing the bath of hyposulphite be kept separate, and that the fingers be well washed before proceeding to take another picture, because contact with this salt spoils both the collodion and nitrate of silver bath.
In fixing the proof, it should not be allowed to remain too long in the bath of hyposulphite, otherwise the fine details will be injured. The entire solution of the iodide of silver is easily perceived by examining the back of the glass. The iodide of silver being of a pale yellow colour is easily seen, and it is, however, necessary that the last traces of this colour be allowed to disappear. When this result is obtained, the glass plate should be taken out and plunged into a bath of cold water.
The solution of hyposulphite will serve a considerable time before it is exhausted, and then it is of so little cost that a fresh solution is easily made.
When the negative proof is immersed in the hyposulphite, the vessel containing it may be taken to the daylight, which will enable the operator better to see when the yellow coating of iodide of silver is quite removed. Ordinary daylight from this time has no action on the picture.
After the fixing is complete, it is of the greatest importance thoroughly to wash the collodion surface especially if a great number of proofs are to be printed from it; this becomes more difficult when the coating has a great tendency to detach itself from the edges of the glass. Nevertheless, even under these circumstances, with a little attention it may be perfectly washed. When the collodion is good, and especially if the gun-cotton has been prepared according to the formula indicated in Note 3, there will not be the least fear of such an accident.
When the film appears liable to detach itself, the small apparatus, Fig. 60, which has already been described, is made use of. The current of water is carefully directed from the middle of the plate towards the edges, constantly varying the inclination in such a way that the water always flows from the centre towards the sides. By these means the coating is prevented, as far as practicable, from being totally removed. Care must also be taken when the glass is left to drain, as the coating wrinkles and bends by its own weight. This effect shows itself while the coating is yet quite wet. When the excess of water has disappeared, a little care will enable the coating to be drawn to its proper position by the aid of the finger.
To properly wash the coating the glass should be placed, during five minutes at the least, in a large vessel of zinc filled with water. If the coating separates in any part the glass must be very gently removed, and the detached parts arranged and brought together by a very fine and light jet of water applied to the required places. W e have often in this way replaced a film upon the glass after it has been entirely removed and torn at the edges, and in spite of all obtained good results.
If the glass be not sufficiently washed after removal from the hyposulphite, the film becomes sticky, and after awhile disappears altogether, or, at least, becomes strongly stained.
It is after removal from the hyposulphite of soda that the proof can be best examined as to its quality. It ought to be of a bluish colour; the sky and high lights a strong black, and the deep shades nearly transparent.
If at this moment, a good photographer judges that his negative is wanting in vigour, he commences another; but if this is impracticable, recourse must be had to intensifying. This operation must be done after the proof is fixed and washed, and before it is dried.
Generally speaking, an intensified negative is worth bat little; and, to repeat, a good operator will rather recommence another negative than intensify. However, if required, the best method is as follows:
The glass plate, after the rinsing which follows the fixing, is plunged into a porcelain vessel containing a solution of bichloride of mercury in water.
|Bichloride of Mercury||to saturation.|
(To saturate the water with bichloride of mercury, this salt, after being powdered, is introduced into a bottle filled with water, and well agitated.)
In a few minutes the coating assumes a milky-white appearance. The plate is now removed and washed with the greatest care, and then plunged into a solution of
|Liq. Ammonia||1 ounce;|
when it immediately becomes darkened. On being taken from this bath the plate is washed with water, and then placed against the wall to drain and dry.
The best method of drying glass plates consists in placing them (Fig. 69) resting by their upper edge against the wall, and their lower edge upon a sheet of bibulous paper, which very quickly absorbs the excess of water.
If the plate is required to be quickly dried, the coated surface ought to be from the wall; and, on the contrary, if it is required to be slowly dried, the coated surface is placed towards the wall. In this latter case, the particles of dust do not so readily attach themselves to the surface of the picture. The intensifying which we have described is very powerful; but it is capable of being regulated, by leaving the plate, for a few seconds only, in the bath of bichloride of mercury. The less time the plate is in the solution, the smaller the quantity of ammonia required to darken it. After a few years, a proof intensified by this method loses its vigour, and becomes even more feeble than it was before. Several other methods for intensifying have been proposed in various photographic works; none of them, however, can be recommended in preference to that described. At the same time, if a good proof be not obtained at the first attempt, by far the better plan will be to try again, as it is by this means alone that real perfection can be attained in the photographic art.