GELATINO-CHLORIDE PRINTING-OUT PAPER Although this paper (commonly known to dealers as P.O.P.) is far from easy to manage in a way that will lead to a high standard of success, it is used by the great majority of amateurs. The advantages connected with it are that there is no need to carry out operations in the dark room, and that, as the image prints out, there are no elaborate calculations of exposure. After one or two attempts any person of ordinary intelligence can judge to what density printing must be carried on, in order that the image may survive the loss of colour incident to toning and fixing. Besides this, by varying the light and time of printing, inferior negatives may be coaxed into giving a passable print. On the whole, it adapts itself to the average negative very well.
Manufacture of P.O.P. paper.—Several formule are given by various authorities. Of these we will only quote two, those of Mr. J. Barker and Mr. W. K. Burton, the stronger proportions of silver, not necessarily giving the best prints.
t. Gelatine (Nelson's No. i and Coignet's) . . . 175 gr.
Ammonium Chloride . . . . . 18 „Rochelle Salts . . . . . . 5o „ Silver Nitrate . . . . . 75 „ Alcohol . . . . . . . 4 dr.
. . . . . . . . . 5 oz. Heat to too" until all has been dissolved and filter.
2. Gelatine . . . . . . 8o gr.
Nitrate of Silver . . . . . 4co „ Ammonium Chloride . . . . • 8o „ Citric Acid . . . . . . . . 120 ,,Water . . . . . . . . . 12 oz.
Dissolve the nitrate of silver in 4 oz. of water, and the other constituents in the remainder of the water. Heat the separate solutions to I lo–I 2o° Fahr., add together, stirring freely, and filter through a double thickness of cambric. For soft negatives add 45 gr., and for very weak negatives So gr. of carbonate of sodium. The emulsion is then floated on a baryta-coated paper, either by hand or the proper machinery. Mr. Burton recommends floating for three minutes on sheets in a room at a temperature of 7o° Fahr. Or the emulsion may be poured on in a small pool and spread quickly over the surface with a brush.
Printing.—There are several excellent brands of P.O.P. and, unless some special kind of paper is to be coated to produce an unusual effect, it is hardly profitable to prepare the above emulsions in practice. They can be bought either
with glossy, matt, or satin surface, each of value for the particular negative ; but it is best in general use to adopt a moderately smooth paper. Place the paper, cut to the proper size, in the printing frame, with the sensitive surface in contact with the film-side of the negative, and add two or three thicknesses of soft paper as padding. Dense negatives may be exposed to the direct rays of sunlight ; weaker ones in a less intense light ; and very thin ones may be shaded with tissue paper or green glass. Examine from time to time by opening one side of the printing frame, taking precautions that the paper does not shift while doing so or a " double print " may result. The printing must be carried to a degree considerably darker than the tone required for the permanent picture, and a slight darkening in the high lights need cause no anxiety.
Clouds.—We have already made some remarks on this subject in the chapter on landscapes. The print may be transferred to another frame in contact with a suitable cloud negative and masked according to the necessities of the case. Where delicate outlines rise high above the horizon the mask may have to take the form of a print, with the sky line carefully cut out with a sharp penknife. In other cases a piece of blotting-paper may be torn roughly into shape, laid on the printing frame outside the glass, and moved up or down during the course of exposure. Fleecy clouds in a blue sky are often imitated with cotton wool or dabs of green paint on the glass side of the negative. But much judgment and skill is needed in the selection of clouds. They should not be introduced at all unless the sky was cloudy when the photograph was taken, and, unless the artist is quite conscious of the effect he is aiming at, he should be content to print them in very lightly. Many a landscape produced on a sunny day has been ruined by the addition of dark, stormy cloud-effects: Sunning Down.—By means of tissue paper, or green water-colour paint on the glass side, certain portions of the negative may be protected from further printing, while the rest is allowed to continue to darken and gain in emphasis.