The difficulties in the process can be overcome by any careful, cleanly manipulator; and amateurs who will follow the directions carefully and intelligently, will have no difficulty in turning out finished prints of their own make, from beginning to end, which will meet the demands of the most exacting, and at a fraction of the cost of the commercial article. It is possible to produce prints of irreproachable purity in the whites, and velvety softness in the blacks, at a cost not exceeding11/2d. a piece for the whole-plate size. The formula for the emulsion is in grains to the ounce of water.
Potassium bromide .. 26 gr.
Water (distilled) .. .. .1 at.
No. 2. Silver nitrate .. .. 32 1/3 gr. Water (distilled) .... 1 oz.
Dissolve the bromide first, then add the gelatine, and dissolve by gentle heat (95° to 100° F.); bring the silver solution to the same temperature, and add in a small stream to the gelatine solution, stirring vigorously, of course, in hon-nctinic light. Keep the mixed emulsion at a temperature of 105° F. for 1/2-l hour, according to the degree of sensitiveness required, previously adding one drop of nitric acid to every 5 oz of emulsion. Allow it to set, squeeze through working canvas, and wash two hours in running water. Yon can manage the washing easily enough by breaking the emulsion up into an earthen jar filled with cold water, and placing in dark room sink. A tall lamp chimney, standing in the jar immediately under the tap, conducts the fresh water to the bottom of the jar, and keeps the finely divided emulsion in constant motion; a piece of muslin, laid over the top of the jar to prevent any of the emulsion running out, completes this simple, in-eipensive, but eflicient washing ap.
The washing completed, you are ready to melt and filter the emulsion preparatory to coating the paper. When melted, and before filtering, it is well to add of glycerine and alcohol each about one-tenth of the whole bulk of the emulsion, the glycerine preventing troublesome cockling of the paper as it dries, and the alcohol preventing air bubbles, and hastening the drying. This addition made, and the emulsion filtered, you are ready to coat your paper, which may be done just as it comes from the stock dealer, plain Saxe or Rives, or better still given a substratum of insoluble gelatine, made as follows:
Gelatine .. .. .. 1 3/5 gr.
Water ......1 oz.
Dissolve and filter; then add 11 drops of a 1.50 filtered chrome-alum solution. The paper is to be floated for half a minute on this solution, avoiding air bubbles, and then hung up to dry in a room free from dust. The purpose of this substratum is to secure additional , brilliancy in the finished prints by keeping the emulsion isolated from the surface of the paper. If you are floating the whole sheet, now is the proper time to cut it to the size you wish to coat, but for anything less thin 6 1/2 x 8 1/2 cut in double or quadruple sizes, 8 x 10 for 5 x 8 and 4x5 prints, as the paper is easily cut down after the emulsion is dry.
A stone, marble, or glass slab large enough to hold at least half a dozen glasses of the size paper you are coating, and most accurately levelled; a dozen or more pieces of glass of the same size as your paper; a porcelain or agate ware tray of the same size; a ruby lamp; a deep tray of a size to hold your jug of emulsion and the smaller tray; a spirit or kerosene lamp enclosed in a box suitably ventilated and protected against the egress of white light from the lamp inside (this is easily secured by punching holes around the top and bottom of a tin box of suitable size and covering it with another somewhat larger in every way, but without a top); and a goodly supply of spring clothes-pins, to be had of any hardware merchant. The above is a complete inventory of the outfit. Add a squeegee muffled with a piece of soft flannel - an article which you can easily make by procuring a piece of small black rubber tubing of the proper length and placing it in the centre of a strip of flannel of equal length and about 2 in. wide; then fold the flannel over on itself, thus inclosing the rubber tube, and fasten the whole between two narrow, thin strips of wood, drawing the rubber up close to the wood.
For coating, you must secure the temporary use of some small room in which the paper can be coated, hung up, and left to dry. This room must meet three requirements; it must be dry, free from dust, and capable of being made absolutely light-tight during the drying of the paper. Into this room, provided with a table large enough to hold your marble slab, on which the slab is carefully levelled, you carry all the articles mentioned above. The spirit or oil lamp is placed in its box, on which stands the large tray previously filled with water at 100° F., and containing the jar of emulsion and the small tray filled with warm distilled water. The ruby lamp stands on a table in front of you; the glasses, well cleaned and warmed to blood heat, and the paper with the side to be coated uppermost are placed on the table at your right; within convenient reach of your right hand stands the tray of warm water, and the levelled slab is within easy reach on your left. Turn the ruby lamp down as low as is consistent with the power of vision.
Now immerse a sheet of the paper in the water in the small tray, leaving it there for a minute or two; then place it accurately on one of the glass plates, and sweep off all superfluous water with the squeegee, at the same time removing all wrinkles and air bells, and place in an upright position to dry slightly while you prepare a second plate in the same manner. Now balance the first plate on the tips of the fingers and thumb of the left hand, and pour on a sufficient quantity of the emulsion, about 1 dr. for every 10 sq. in. of paper. You can use a silver soup ladle holding just enough to cover a whole plate. Gently tilt plate from you until the further end is completely covered; then as gently tilt it toward you until the emulsion completely covers the paper; then carefully place it on the levelled slab to set. Continue this operation until the slab is covered, when the paper first coated will probably have become sufficiently set to be stripped from the glass and hung up by clothes-pins to dry, requiring 6-10 hours.
The exposure is somewhat long. With negatives of ordinary density, and a kerosene lamp with a 1 1/2 in. wick, 1-1 1/2 minutes is about right, the negative being held about 18 in. from the lamp. Considerable latitude of exposure is given by this process, which is a great advantage. The developer is ferrous oxalate, in the proportion of 1 part of iron to 5 or 6 of oxalate, adding more iron occasionally to strengthen. Both the iron and oxalate solutions should be kept slightly acid; use no bromide, which ruins the tone and diminishes detail. Of course, the acid clearing solution - 1 dr. acetic acid to 32 oz. water - should be used.
Negative paper is prepared in the same way, substituting a more rapid emulsion for the slow one given above.
It may be worth noting that very good matt surface prints can be made by coating ordinary drawing paper of light or medium weight with this emulsion, but for contact printing from small negatives the results are rather coarse. - (R. W. Burbank.) (See also iv. 344.)