Perhaps of all the various arts discovered by man, this is the most beautiful, producing a perfect likeness of any being or object in a few moments, and with a truth not to be equalled by years of study and practice in other ways. One of the earliest discovered and simplest modes of forming a sun picture consists in using the object itself (where this is possible) to form the negative. This can only be done when the object is flat, as a manuscript, a picture, a leaf, or a piece of lace-work; a piece of paper washed over with a solution of common salt, dried, and again washed over with a solution of nitrate of silver, will answer for this purpose; it should be prepared by candle-light, as daylight blackens it, and it should be kept from the light till the moment for use. If this paper, having the object to be copied placed on it and kept flat by a piece of glass pressed firmly on by a contrivance shown in [fig. 4], be exposed to the sunshine, it will be blackened in all places but those kept from the light by the darker parts of the object, and the lights and shadows will vary accordingly as the various parts of the object itself are more or less transparent. When the effect has been produced to a sufficient degree, the paper should be removed and at once washed in a solution of hyposulphite of soda, which removes all the superfluous silver (which otherwise would be darkened by the light); when removed from the hyposulphite of soda it should be well soaked in clean water. This when finished is a true negative picture of the object, and can be used to produce the positive. The negative should first be made partly transparent by brushing it over with some melted white wax, then placing it between folds of blotting paper and passing a hot iron over it, the blotting paper will absorb all the superfluous wax, and the negative will be fit for use. A piece of paper prepared like the first with salt and nitrate of silver, should be placed against the front of the negative, kept smooth by a piece of glass, and exposed to the sunshine for a quarter of an hour or more, taking care that the back of the negative is exposed to the light and the prepared paper behind; a positive picture will be produced, which is to be at once treated with a solution of hyposulphite of soda and washed with clean water, as was the negative. Any number of positive impressions may thus be produced.
The “Calotype” or “Talbotype” process may be performed as follows, recollecting that all these processes must be conducted by candlelight, or in a room having the window covered with yellow silk, or some other substance excluding white light. Select a piece of paper of an even surface and structure, such as Whatman’s paper, brush it over with a solution of nitrate of silver—about sixteen grains to an ounce of water—and let it dry, then fold up the edge of the paper all round and dip the surface to which the solution of nitrate of silver has been applied into a solution of iodide of potassium—an ounce to a pint of water—contained in a shallow vessel, and let it partly dry; float it for a quarter of an hour in a vessel of clean water, moving it gently about so as to remove all soluble matter, and hang it up by a corner to dry, taking care to let nothing touch the surface. When about to be used, this paper must be brushed over (using a soft camel-hair brush) with a mixture, in equal quantities, of a solution of nitrate of silver—fifty grains to an ounce of water—and a saturated solution of gallic acid, forming what is called the “gallo-nitrate” of silver. Leave this solution on the surface for ten minutes, and again immerse the paper in two or three successive portions of pure water, moving it to and fro; this, when nearly dry, is in a fit state to place in the camera, and is an exceedingly sensitive paper, which in a good light will be affected in a few seconds. When the image has been impressed by the camera, the paper should again be brushed over with the gallo-nitrate of silver, and held either near a fire or a plate of hot iron, so as to receive a gentle warmth; the impression will now come out, of a deep rich colour. Dip it into warm water for a few minutes, and put it into the hyposulphite of soda bath—an ounce to a quart of water—from which it is finally removed and placed in a large vessel of pure water for several hours. When dry, it is complete, forming a good negative, which, when waxed, may be used to print positives as before described.
The “Collodion” process is conducted as follows. Having selected a plate of glass of the required size and of good quality (patent plate answers well), clean it thoroughly with rottenstone and spirits of wine, and polish it with a clean dry linen cloth; then hold it on the tips of the fingers and thumb in a horizontal position, pour upon it a small quantity of the “iodized collodion,” and so incline it from side to side, that all the surface shall be covered with the collodion, that which is superfluous being returned to the bottle by pouring it from one corner of the glass. In a few minutes the coating of collodion will be dry, and should form a perfectly even surface, without air spots or uneven markings. The iodized collodion is made by dissolving gun-cotton in ether, and adding spirit of wine and iodide of ammonia. The glass plate coated with collodion is now dipped into a solution of nitrate of silver—thirty grains to an ounce of water—and allowed to remain two or three minutes; when all the superfluous fluid has drained off, the plate is ready for use, and is extremely sensitive to light. When the impression has been produced by the camera, a solution of pyro-gallic acid, mixed with a little acetic acid, is poured over the surface, which brings up the image; when this is developed to a proper extent, the surface must be washed with clean water and afterwards with a solution of hyposulphite of soda, which dissolves out all the silver from those parts not darkened by the light in the camera, leaving the glass in those parts quite transparent. A negative is thus obtained fit to print from in the usual way, but glass being more transparent than the waxed paper, it produces a more perfect positive. The surface thus prepared should be coated with a varnish, made by dissolving amber in chloroform, which is done by pouring it on and decanting the superfluous varnish similarly to the mode of coating with collodion; this varnish dries in a few minutes, and preserves the surface from injury. Sometimes these negatives are converted into positives, instead of being used to print from; in these cases the surface is coated with black japan, and the collodion, having a whitish surface, owing to reduced silver, shows up in comparison with the black varnish which is seen through the transparent parts. These positives are extremely sharp and well defined.
The “Daguerreotype” process consists in forming the image on the surface of a metallic plate (copper coated with silver), which is first polished to a perfect surface like a looking-glass, then exposed to the vapour of iodine in a properly-constructed box, afterwards to the vapour of chloride of bromine, and again to the vapour of iodine; this produces a thin film of a mixture of bromide and iodide of silver, which covers the surface of the plate, and is very sensitive to light, which reduces the iodide and bromide to the metallic state in a few seconds. The plate is then exposed to the action of the light in the camera, and when sufficiently affected, exposed to the vapour of mercury, the mercury being put into a box, and heated by a spirit lamp; the mercurial vapour adheres to all the parts of the silver reduced by the light, and forms a light-coloured amalgam, corresponding to the lights of the objects represented. The plate is then washed with a solution of hyposulphite of soda, which removes all the bromide and iodide of silver not reduced by the light, and exposes the highly-polished surface of the silver, which forms the shadows of the picture; this is now “fixed” with a very weak solution of chloride of gold and hyposulphite of soda, which is poured over the surface and heated while there by applying the flame of the spirit lamp to the back of the plate for a minute or two; the solution is then poured off, and the picture when washed with water is complete.
FIG. 5.
FIG. 6.
Many photographic pictures, whether Talbotype or Daguerreotype, are taken double for the “stereoscope” ([fig. 5]). This is an instrument having two lenses (one for each eye), through which the two views may be seen. The principle is this:—Every object is seen by each eye in a slightly different view; for instance, if you look at the edge of a print—placing the printed part towards your right hand, and bringing the edge in front of the lace between the two eyes—by closing the right eye, the left will see the back of the print only, but by closing the left eye the front of the print may be seen, and the front only. The stereoscope presents both of these views to the eyes at once, as when we look with both eyes, and the objects have therefore the appearance of projecting, as do read objects. To take these views, the slide after one view is taken is moved about four inches on one side, and then the other is taken; the distance moved corresponds to the distance between the eyes, and therefore produces the correct view for each. The box for the stereoscopic slide is shown at [fig. 6], in which A is the first view to be taken, while the other half of the glass is kept dark, at B, and C is the shutter for A.