The photographic printing frame is made of wood, generally teak, and can be bought in the usual sizes of plates. The negative fits into a rebate, and is placed in position film side upwards. Upon this a piece of sensitive paper previously cut to size, is laid with its shiny albumenized surface touching the surface of the film. A few folds of clean blotting paper or a pad of felt is next placed above the paper, and then the hinged back of the printing frame covers up the entire arrangement. The two metal springs are now brought over and placed in position, and all is ready for exposure to the active rays of the sun. The hinged back is so arranged that by displacing one of the springs, half of the back board can be folded over, and the paper can be examined in a dull light so as to watch the progress of printing.
A novel kind of printing frame has been recently introduced which is known as Durnford's printing frame. It is shown at page 127. Many will be attracted by its small volume, which renders it especially valuable to those who prefer to carry their printing requisites from place to place with them. It consists of a hinged board covered with cloth. At the back, not shown in the wood-cuts, are two springs, provided at each end with stirrup-shaped catches, which can be bent over to clutch the negative placed upon the board. The stirrups are furnished with rubber cushions to obviate any chance of breaking the glass. A sheet of sensitive paper is put between the negative and the board. In the cut, one pair of stirrups has been released, so that the print can be examined in the same way as in the more common form of frame.
As in the taking of a negative no fixed rule can be given as to the time of exposure, but in the one case it is a matter of seconds, and in the other it may be a question of hours. The time will depend upon the density and the colour of the negative, and also upon the available light. A black and white negative with cool grey half-tones, such as ferrous oxalate gives, will print on a favourable day in about fifteen minutes. A negative treated by ammonia or soda development, may require double that time, for the colour of the film is of a less actinic quality. On a dull day, again, the first named negative may require an hour's exposure or more, and of course the other negative will require under the same conditions a proportionate increase in the time of exposure. A poor thin negative will never give a really good print, but by modyfying the amount of light submitted to it, a much better result can be obtained than if it were treated as a thoroughly good one. Indeed, the amount of light allowed to fall upon the printing frame must in all cases depend upon the nature of the negative. Never must the direct rays of the sun be employed unless the negative be of quite; exceptional density, and when therefore a print cannot be otherwise obtained. Diffused daylight must be the rule, that is to say, the printing frames must be exposed where only the reflected rays from the open sky can reach them; as, for instance, on some support such as a window ledge on the shady side of a house. A thin negative may be exposed in the same position, but it should be protected by a covering of red or yellow tissue paper, so that the printing action is rendered much slower. The same result can be obtained by giving it a long exposure inside a room, at some distance from the window.
In any case the action must be watched by folding back the half of the back printing frame as already indicated. And in all cases the action should be allowed to continue until the print looks far more deeply printed than would be desirable in a finished picture. The reason of this is, that the image loses much of its force in the subsequent operations.
It is not worth while to undertake the necessary, and all times somewhat tedious operations of printing, toning, and fixing for one or two pictures, for the work involved is much the same if a single print or several dozen are taken in hand at the same time. And although, for the sake of simplicity, we will write as if only a single print were in question, it must be understood that our remarks apply to a batch. Let a fine day be chosen for the work, or it will prove tedious indeed, and let at least three or four printing frames be employed, according to the number of negatives upon which the operator is at work. One word more, do not attempt to print while other work is going on, or several prints will be left to themselves too long, and will be over printed.