HE latest and most rapid advance in the art is due to the discovery of the sensitiveness of a gelatine film. This knowledge has been practically ap-plied in the introduction of plate prepared with such a coating; they are called "dry plates," to distinguish them from plates which must pass through the silver bath, and be used while wet. The gelatine-bromide dry plates are now in genera! use for taking pictures of out-door scenes, landscapes, houses, groups of people, etc. To make photographs, First Procure an Outfit from a dealer in photograph requisites, costing from ten to twenty-five dollars, consisting of a view camera, for making 4x5 or 5x8 inch pictures. This camera is so constructed as to make either a picture on the full size of the plate (5x8 inches), or by substituting the extra front (supplied with the outfit), and using the pair of lenses of shorter focus, it is admirably adapted for taking stereoscopic negatives. Also, by the same arrangements, two small pictures, of dissimilar objects, can be made on the same plate. Included in the outfit, are also one patent double dry-plate holder, one large achromatic nickel plated lens, one pair "Waterbury" achromatic matched stereoscopic lens, one Taylor folding tripod, one carrying case.
Filling the Plate Holder. If this is done in the daytime, a closet or room is selected, and all white light excluded from it.
It is difficult to make this exclusion absolute. One ray of white light will spoil a sensitive plate, and therefore the evening is generally chosen to develop negatives, and for illumination, the light from a ruby lantern is employed.
Gelatine Plates are glass, with one side coated with gelatine, containing a haloid salt. Place one of them in a dry-plate holder, with the sensitive (or the coated) side facing outward. Handle the plates by the edge, between the thumb and fore finger, without touching the sides. After putting into the holders as many plates as are needed for the day's work, pack the outfit so that it can be carried about.
Taking the Picture. For field service a camera, a number of plate holders, filled with sensitive plates, a lens, tripod, carrying case, and focussing cloth are needed. When these have been taken to the place which you want to photograph, fasten the camera on the tripod, throw the focussing cloth over your head, gather it under your chin, draw out the back of the camera, thus extending the bellows, and continue the movement until the image on the ground glass appears distinct, then fasten the back of the camera. This is called "focussing." At the first glance, an inexperienced person sees no reflection on the ground glass, but the eye soon becomes practiced to perceiving the inverted image there. Substitute a plate holder for the ground glass, see that the cap is on the lens, pull the slide out of the holder, place it on the top of the camera, or in a convenient place. If everything is now in readiness, and the time for exposing the sensitive plate determined, uncap the lens, re-capping it at the end of the allotted time, and replacing the slide in the holder. After you have picture impressions on each sensitive film, pack your outfit and return home.
Making Negatives. Amateurs may content themselves with making the exposures, and sending their plates in a light, tight, negative box, to some photographer, who will produce the finished picture, and mount them on cards. It is not necessary that this should be done at once, months may elapse, and these dry plates be carried hundreds of miles.
The chemical outfit for making negatives comprises the following items: Two vulcanite trays, a glass graduate, a set of small scales, and weights for weighing chemicals, a ruby lantern, a bottle of varnish, a package of dry plates and of chemicals, a small quantity of bromide of ammonium, neutral oxalate of potash, protosulphate of iron, hyposulphite of soda, alum, and sulphuric acid. These chemicals are not dangerous, neither will they injure any one who handles them, and they do not emit offensive odors. Silver stains, and the disagreeable smell of collodion belong to the old or "wet" process.
At a convenient time take the plate holder into the dark room, illuminate it with ruby light, take the sensitive plates out of the holders, being careful not to touch their surfaces. Hold them by the edge. Place one of the sensitive plates, film side up, in a tray partly filled with water. While it remains there, mix this solution: Neutral oxalate of potash, 5 ounces; bromide of potassium, 20 grains; water, 20 ounces. If the solution does not turn blue litmus paper red, add a few drops of oxalic acid, enough to make it do so. A graduated glass is used to measure out the liquids. After rinsing the glass out, mix a second solution made as follows: Protosulphate of iron, 5 ounces; water, 20 ounces; and acidulate it with 20 drops of sulphuric acid. Both of these solutions keep well. Now combine a quarter of an ounce of the latter solution with two ounces of the former and mix them well. Pour off the water in the tray containing the gelatine plates. Be certain not to touch the sensitive side of the plate. Flow the combined developing solution over the plate and displace, by a touch of your finger, any air bubbles that may form. After a short time traces of the image on the sensitive film will appear. If they do not, pour the developing solution back into the tray and add a quarter of an ounce more of the iron solution. Pour the strengthened solution over the plate and look at it intently. In a short time the details of the picture may be dimly seen. Wait patiently till the milky white appearance is changed to a grey color, and then pour off the developer into a developing bottle, if you have one. Wash the plate in two changes of water. In the unused tray mix a solution composed of 4 ounces of hyposulphite of soda and 20 ounces of water. (Label this tray " Hypo.," and do not use it for any other purpose.) A plate lifter is a convenient device for taking plates out of the solutions or baths. Change the plate to the hypo, tray, and let it remain there until every vestige of the milky white appearance has vanished, even from the under surface of the plate. The plate can now be examined by white light, which has no effect upon it at this stage. Wash it thoroughly. A negative washing box will be found to be of great assistance. If this washing of the plate is not done thoroughly, the hyposulphite of soda crystals will adhere to the plate and mar the picture. Meanwhile rinse out the tray first in use and partially fill it with a solution consisting of 20 ounces of water and all the alum it will hold in solution. Allow the plate to remain in the alum bath five minutes. Cleanse your hands from any adhering soda solution. Again wash the plate, and set it on edge to dry in a negative rack.
All the preceding instructions can be briefly summarized.
1. Put some sensitive plates into dry plate holders.
2. Make the exposure.
3. After taking a plate out of the holder, place it in a tray filled with water.
4. Drain off the water and put the plate in the mixed developing solution.
5. Wash the plate and place it in the soda solution.
6. Wash the plate and give it an alum bath.
7. Wash the plate and set it in the rack to dry. When perfectly dry, coat the plate over with negative varnish, and have that coating dry and hard, Now it may be touched by the fingers.
Making Prints from Negatives. At this point the work ceases to be one of faith, as the results are now to appear. An outfit of printing requisites comprises a printing frame, a porcelain pan, a vulcanite tray, some ready sensitized paper, a bottle of French azotate, a bottle of chloride of gold, a glass graduate, some hyposulphite of soda, a glass form, a Robinson trimmer, some sheets of fine card-board, a jar of parlor paste, and a bristle brush.
Sensitized Paper Prints. In the morning prepare a toning bath sufficient for the prints to be toned that day. Put 7 1/2 grams of chloride of gold into 7 1/2 ounces of water. Label the bottle "Chloride of Gold Solution." Take 1 ounce of French azotate, 1 1/2 ounces of the chloride of gold solution, and add 6 ounces of water, and you have a toning bath which keeps well. Where the prints do not give the required tone, the bath must be strengthened by adding to it some new solution. Place the glossy side of a sheet of sensitized paper upon the film side of the negative in the printing frame. Do this in a very dim light.
The printing has gone far enough when the print looks a little darker than you wish the finished picture to appear. Make as many prints from the negative as you desire. Wash the prints in several changes of water. Take seven ounces of the toning solution and change the prints to the pan containing it, where the prints should be turned over and over to make the toning even. The toning process should go on until the dark part of the pictures have a very faint purplish tint and the white portion is clear. Wash the picture, but preserve the toning solution. The pictures should now be left for twenty minutes in a solution composed of 4 ounces of hyposulphite of soda, 1 ounce of common salt, 1/2 ounce of washing soda, and 32 ounces of water. This solution should also be prepared a day or two in advance. Give the pictures a final and effectual washing. After they are dried, lay them out one by one and, using the Robinson trimmer, cut them to the desired size. Now spread over the back of each in turn some parlor paste, and lay them down with the center on the sheets of card-board. This operation is called "Mounting Pictures." Press with a paper cutter upon the pictures and toward their edges until you are satisfied that they will lay flat,