A common method of rendering paper negatives transparent is by means of vaseline. Although a special vaseline oil has been prepared for this purpose, the ordinary substance used as a pomade will answer very well. One method of applying it is to rub the vaseline thickly over the back of the negative, and then hold it near a fire so that the oil will melt and run well into the fibers of the paper. One of the drawbacks to the use of vaseline for this purpose is the necessity of always keeping the negatives treated with it between sheets of oiled paper to preserve the vaseline from evaporating when not in use for printing from.
It should be noted that before rendering a paper negative translucent it is always advisable to make a print, as with many negatives a better positive is obtained without oiling.
TRANSPARENCY.—In art, a picture painted or photographed on transparent or semi transparent material, such as glass, thin paper, etc., to be viewed by the natural or artificial light shining through it.
Under this heading we will give the different processes of obtaining transparencies from an ordinary negative for various purposes, such as for window transparencies, lantern slides, stereoscopic slides, and also for making fresh negatives from a negative by first making a positive transparency.
There are a very great variety of methods,the simplest being,of course,the simple exposure of an ordinary dry plate behind a negative, and development,usually with or other method which gives a more artistic tone than the useful pyro.
A good developer, giving pleasing black tones, is the following, recommended for " Paget Prize " plates by the manufacturers, these plates being very suitable for transparencies :— No t.
H ydroki none r ounce Methylated spirit to ounces Sulphurous acid ounce Potassium bromide ounce Dissolve the hydrokinone in the spirit, and add the acid. In another vessel dissolve the potassium bromide in 3 ounces of distilled water. Mix the two solutions, and make up to 20 ounces with distilled water.
No. 2.
Caustic soda (in sticks) t ounce Sodium sulphite 5 ounces Distilled water to make zo ounces One part of each of these two solutions to four parts of water. If too hard, more water should be added In the making of lantern slides or transparencies upon ordinary gelatino bromide plates, the chief drawbacks are in the production of clear lights and brilliancy. A brand of plates should be chosen possessing a fairly thick coating. Authorities differ on the advisability of adding a little chloride to the emulsion for the purpose of im proving the color. Others again recom mend iodide for warm tones.
With a variety of developers a number of different effects can be produced, and colors of all kinds and shades to suit the taste of the worker can be obtained. The ferrous oxalate developer is one that is very generally used, and gives very good cold black tones. After developing, fixing and well
washing, Pringle recommends a clear ing solution composed of a very strong and saturated solution in water of alum and citric acid, to each pint of which about two drachms of hydrochloric acid are added.
Mr. F. C. Beach recommends the following eikonogen developer as a suitable one for lantern slide trans parencies, giving a bluish black tone similar to the palladium or platinum tone usually given to wet-plate slides. The proportions are— Sulphite of soda to grains Eikonogen 5 grains Carbonate of potash 2 grains Water t ounce This developer made up as recommended above will develop from seven to ten slides in suc cession. The rapidity of its action can, if desired, be retarded by adding a few drops of a ten grains to the ounce solution of potassium bromide.
Another method of making transparencies, or lantern slides, is by means of Alpha plates. These plates are placed upon the market ready for use, one of their peculiarities being the extra ordinary latitude of exposure. Thus, from one negative, a number of perfect slides can be ob tained with different exposures of from one to three minutes, all possessing the same depth, but differing in the color in the following order—greenish black, olive green, cold brown, brown, reddish brown, red, yellowish red. It will thus be apparent that it is possible to so arrange the exposure as to get the color most desired or the one most suitable to the subject. Besides the colors already stated, a further variety can be obtained by toning with the formula used in the combined fixing and toning bath recommended for use with the Alpha paper.
Water to ounces Hypo 24 ounces (Avoirdupois) Acetate of soda ounce (Avoirdupois) Ammonium sulphocyanide f ounce (Avoirdupois) Gold chloride 4 grains This is used instead of the ordinary fixing bath, and the slide can be toned any time after fixing, The brown developed slides give the greatest range of tone in the toning bath.
A most beautiful process for the production of transparencies is the albumen process, al though the difficulty of working it has prevented its use from being more universal. A descrip tion of the process will be found in another place. (See Albumen Process.) Transparencies can also be produced by means of printing-out emulsions. A formula is given under the heading treating of gelatino-citro-chloride printing processes. Instead of spread ing this emulsion upon a paper support, glass can be coated with it, and transparencies produced. Of course, the printing must be carried very far to get any degree of density when viewed by transmitted light.
Other methods of producing transparencies are by means of the carbon process, the col lodio-chloride process, etc., all of which will be found treated upon in their various places.