Part 4 (2/2)

In the process giving blue lines upon a white ground, it is necessary that the action of the light shall be to convert the iron compound into one that can be discharged from instead of being fixed on the paper, so that we obtain a positive from a positive. Abney describes the process as follows: Thirty volumes of gum solution (water 5 parts, gum 1 part) are mixed with 8 volumes of a citrate of iron and ammonia solution (water 2 parts, double citrate 1 part), and to this is added 5 volumes of a solution of ferric chloride (water 2 parts, ferric chloride 1 part). This solution thus formed is limpid at first, but will gradually become thicker, and should be used soon after mixing.

It is then applied with a brush to the paper (which should be well sized) and dried in the dark. Exposure is accomplished in a few minutes, the paper being placed under the drawing in the printing frame. It is then developed with pota.s.sium ferrocyanide, 50 grains, water 1 ounce, applied with a brush until all the details appear of a dark-blue color. The print is then rapidly rinsed, and placed in a dish containing the clearing solution, made of 1 ounce of hydrochloric acid and 10 ounces of water.

The third process, which gives violet-black lines on a white ground, is the following: Make up the sensitive solution with water, 16 ounces; gelatine, 4 drachms; perchloride of iron (in a syrup condition), 1 ounce; tartaric acid, 1 ounce; sulphate of iron, 4 drachms. The paper is floated on or brushed over with this and dried.

The exposure is about the same as with the last process. When sufficient, the greenish-yellow color will turn white, except the lines, which should be somewhat dark. The developing solution is composed of 1 part of gallic acid in 10 parts of alcohol and 50 of water. When immersed in this solution the lines will turn blacker. The finish is then made by thoroughly was.h.i.+ng in water.

SYMPATHETIC PHOTOGRAPHS.

These are obtained as follows: A sheet of paper is coated with a ten per cent solution of gelatine, and when dry this is floated on a ten per cent solution of b.i.+.c.hromate of potash. Again dry and expose beneath a positive transparency. The print thus obtained is then immersed in a ten per cent solution of chloride of cobalt. The parts unacted upon by light will absorb the solution. Wash and dry. We then have a faint image which will alter its color according to the state of the atmosphere. In damp weather it will be almost if not entirely invisible, but when the weather is fine and dry, or if the image be heated before a fire it will turn to a bright blue color.

DRY-PLATES THAT WILL DEVELOP WITH WATER.

Some time ago dry-plates were placed on the market which would develop, apparently, with water and a little ammonia only. The secret of the method was that the backs of the plates were coated with a soluble gum, containing the developing agents, and, of course, when the plate was immersed in the water, they instantly dissolved and formed the developer. Plates thus prepared are useful in traveling where it is not always possible to get the necessary developing solutions. To prepare them the backs are coated with the following mixture:

Pyrogallic acid 154 grains Salicylic acid 15 grains Gum or dextrine 154 grains Alcohol 1 fluid dr.

Water 5 fluid dr.

This is allowed to dry at an ordinary temperature. After exposure, all that is necessary to develop is to immerse the plates in water containing a small quant.i.ty of ammonia.

CARICATURE PHOTOGRAPHS.

There are quite a number of different methods of making caricature portraits. A simple one is to make two photographs of an individual, one of the head alone and another of the entire body on a much smaller scale. From these two negatives prints are made, and the larger head is cut out and pasted on the shoulders of the full length figure. Any signs of the cutting out are removed by the use of a brush and a little coloring matter. From this combined print another negative is made so that any number of these caricature prints can be made without extra trouble. The effect is shown in Fig. 44.

[Ill.u.s.tration: From Tissandier's Handbook. FIG. 44.--CARICATURE PORTRAIT.]

Foregrounds for making caricature portraits are sold in this country.

The method of using them is shown in Fig. 45. The card containing the grotesque drawing is held by the sitter on his knees and arranged by the photographer in such a way that his head rests just above the neck of the painted body. A white background is arranged behind and when the negative is made all traces of the edges of the foreground are removed by careful re-touching.

[Ill.u.s.tration: FIG. 45.--CARICATURE]

[Ill.u.s.tration: FIG. 46.--MAKING THE CARICATURE PORTRAIT.]

Another method of obtaining grotesque caricature portraits has been devised by M. Ducos du Hauron. His apparatus, which he calls ”La Photographie Transformiste,” is thus described by Schnauss in his ”Photographic Pastimes.” A, Fig. 47, is the front of the box, which is furnished with an exposing shutter formed of a simple sliding piece fitting into the grooves R R, R R. B P are two screens pierced with slits _a a_, _c c_. C is the rear end of the box where the dark slide is placed. D is the lid of the box, which is lifted either for placing the slotted screens or for putting in the sensitive plate. When not working direct from nature, the transparency is placed in the grooves R R, R R, at A.

[Ill.u.s.tration: FIG. 47.--THE HAURON ”TRANSFORMISTE.”]

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