For this purpose we must quit the warm precincts of the cheerful day, and go into the narrow den where the deeds of darkness are done. Its dimensions are of the smallest, and its aspect of the rudest. A feeble yellow flame from a gas-light is all that illuminates it. All round us are troughs and bottles and water-pipes, and ill-conditioned utensils of various kinds. Everything is blackened with nitrate of silver; every form of spot, of streak, of splash, of spatter, of stain, is to be seen upon the floor, the walls, the shelves, the vessels. Leave all linen behind you, ye who enter here, or at least protect it at every exposed point. Cover your hands in gauntlets of India-rubber, if you would not utter Lady Macbeth's soliloque over them when they come to the light of day. Defend the nether garments with overalls, such as plain artisans are wont to wear. Button the ancient coat over the candid shirt-front, and hold up the retracted wristbands by elastic bands around the shirt-sleeve above the elbow. Conscience and nitrate of silver are telltales that never forget any tampering with them, and the broader the light the darker their record. Now to our work.
Here is a square of crown glass three-fourths as large as a page of the "Atlantic Monthly," if you happen to know that periodical. Let us brush it carefully, that its surface may be free from dust. Now we take hold of it by the upper left-hand corner and pour some of this thin syrup-like fluid upon it, inclining the plate gently from side to side, so that it may spread evenly over the surface, and let the superfluous fluid drain back from the right hand upper corner into the bottle. We keep the plate rocking from side to side, so as to prevent the fluid running in lines, as it has a tendency to do. The neglect of this precaution is evident in some otherwise excellent photographs; we notice it, for instance, in Frith's Abou Simbel, No. 1, the magnificent rock-temple façade. In less than a minute the syrupy fluid has dried, and appears like a film of transparent varnish on the glass plate. We now place it on a flat double hook of gutta percha and lower it gently into the nitrate-of-silver bath. As it must remain there three or four minutes, we will pass away the time in explaining what has been already done.
The syrupy fluid was iodized collodion. This is made by dissolving gun-cotton in ether with alcohol, and adding some iodide of ammonium. When a thin layer of this fluid is poured on the glass plate, the ether and alcohol evaporate very speedily, and leave a closely adherent film of organic matter derived from the cotton, and containing the iodide of ammonium. We have plunged this into the bath, which contains chiefly nitrate of silver, but also some iodide of silver,—knowing that a decomposition will take place, in consequence of which the iodide of ammonium will become changed to the iodide of silver, which will now fill the pores of the collodion film. The iodide of silver is eminently sensitive to light. The use of the collodion is to furnish a delicate, homogeneous, adhesive, colorless layer in which the iodide may be deposited. Its organic nature may favor the action of light upon the iodide of silver.
While we have been talking and waiting, the process just described has been going on, and we are now ready to take the glass plate out of the nitrate-of-silver bath. It is wholly changed in aspect. The film has become in appearance like a boiled white of egg, so that the glass produces rather the effect of porcelain, as we look at it. Open no door now! Let in no glimpse of day, or the charm is broken in an instant! No Sultana was ever veiled from the light of heaven as this milky tablet we hold must be. But we must carry it to the camera which stands waiting for it in the blaze of high noon. To do this we first carefully place it in this narrow case, called a shield, where it lies safe in utter darkness. We now carry it to the camera, and, having removed the ground glass on which the camera-picture had been brought to an exact focus, we drop the shield containing the sensitive plate into the groove the glass occupied. Then we pull out a slide, as the blanket is taken from a horse before he starts. There is nothing now but to remove the brass cap from the lens. That is giving the word Go! It is a tremulous moment for the beginner.
As we lift the brass cap, we begin to count seconds,—by a watch, if we are naturally unrhythmical,—by the pulsations in our souls, if we have an intellectual pendulum and escapement. Most persons can keep tolerably even time with a second-hand while it is traversing its circle. The light is pretty good at this time, and we count only as far as thirty, when we cover the lens again with the cap. Then we replace the slide in the shield, draw this out of the camera, and carry it back into the shadowy realm where Cocytus flows in black nitrate of silver and Acheron stagnates in the pool of hyposulphite, and invisible ghosts, trooping down from the world of day, cross a Styx of dissolved sulphate of iron, and appear before the Rhadamanthus of that lurid Hades.
Such a ghost we hold imprisoned in the shield we have just brought from the camera. We open it and find our milky-surfaced glass plate looking exactly as it did when we placed it in the shield. No eye, no microscope, can detect a trace of change in the white film that is spread over it. And yet there is a potential image in it,—a latent soul, which will presently appear before its judge. This is the Stygian stream,—this solution of proto-sulphate of iron, with which we will presently flood the white surface.
We pour on the solution. There is no change at first; the fluid flows over the whole surface as harmless and as useless as if it were water. What if there were no picture there? Stop! what is that change of color beginning at this edge, and spreading as a blush spreads over a girl's cheek? It is a border, like that round the picture, and then dawns the outline of a head, and now the eyes come out from the blank as stars from the empty sky, and the lineaments define themselves, plainly enough, yet in a strange aspect,—for where there was light in the picture we have shadow, and where there was shadow we have light. But while we look it seems to fade again, as if it would disappear. Have no fear of that; it is only deepening its shadows. Now we place it under the running water which we have always at hand. We hold it up before the dull-red gas-light, and then we see that every line of the original and the artist's name are reproduced as sharply as if the fairies had engraved them for us. The picture is perfect of its kind, only it seems to want a little more force. That we can easily get by the simple process called "intensifying" or "redeveloping." We mix a solution of nitrate of silver and of pyro-gallic acid in about equal quantities, and pour it upon the pictured film and back again into the vessel, repeating this with the same portion of fluid several times. Presently the fluid grows brownish, and at the same time the whole picture gains the depth of shadow in its darker parts which we desire. Again we place it under the running water. When it is well washed, we plunge it into this bath of hyposulphite of soda, which removes all the iodide of silver, leaving only the dark metal impregnating the film. After it has remained there a few minutes, we take it out and wash it again as before under the running stream of water. Then we dry it, and when it is dry, pour varnish over it, dry that, and it is done. This is a negative,—not a true picture, but a reversed picture, which puts darkness for light and light for darkness. From this we can take true pictures, or positives.
Let us now proceed to take one of these pictures. In a small room, lighted by a few rays which filter through a yellow curtain, a youth has been employed all the morning in developing the sensitive conscience of certain sheets of paper, which came to him from the manufacturer already glazed by having been floated upon the white of eggs and carefully dried, as previously described. This "albumenized" paper the youth lays gently and skilfully upon the surface of a solution of nitrate of silver. When it has floated there a few minutes, he lifts it, lets it drain, and hangs it by one corner to dry. This "sensitized" paper is served fresh every morning, as it loses its delicacy by keeping.
We take a piece of this paper of the proper size, and lay it on the varnished or pictured side of the negative, which is itself laid in a wooden frame, like a picture-frame. Then we place a thick piece of cloth on the paper. Then we lay a hinged wooden back on the cloth, and by means of two brass springs press all close together,—the wooden back against the cloth, the cloth against the paper, the paper against the negative. We turn the frame over and see that the plain side of the glass negative is clean. And now we step out upon the roof of the house into the bright sunshine, and lay the frame, with the