Lantern plates may be bought to give either warm or cold tones. The size of the lantern plate is 3 1/4 inches square, therefore it is somewhat smaller lengthways than a quarter-plate; but it frequently happens that the sacrificing of this odd inch when working with a quarter-plate negative does not affect matters, and very effective lantern slides can be made from this popular size.
All operations until after fixation must be carried out in the dark-room.
Lantern slides are made either by contact or reduction.
Supposing, then, a quarter-plate negative is to be printed from, it is laid in the printing-frame in the usual way, and upon it a lantern plate; care should be taken not to scratch the one with the other. Hold up the frame so that the light from the dark-room lamp may pass through it. Carefully move the lantern plate to and fro until it includes the portion of negative that will make the best picture. Replace the back, and all is ready for exposure; if the frame has to be taken from the room for this purpose it must be covered up.
The length of exposure will depend upon the character of the negative and source of light. As a first attempt, it will be as well to select a fairly strong negative to the working of which in other printing media the worker is accustomed, and make trial exposures. A fast (blackand-white) lantern plate exposed under it at a foot from an ordinary gas flame might be given five, ten, and fifteen seconds' exposure by uncovering in the usual way. When the correct time is found, a lantern plate should be exposed, developed and fixed. By experimenting in the early stages in this way, the worker will soon acquire a fair idea of how long exposure to give with the general run of negatives.
When a lantern slide is required from a negative larger than a quarter-plate, it must be done by reduction. This operation may be regarded as just the reverse of making an enlarged positive. The negative is placed in the opening of the window-shutter and the camera is brought some distance along the support or ledge; this time it is turned with the lens pointing towards the negative. For the time being the easel is moved out of the way, as it is not required, the ordinary back and dark-slide of camera taking its place.
The dark-slide should be provided with a carrier to hold the lantern plate, and the focussing screen marked with pencil in such a manner that the markings will come exactly in front of the spot to be occupied by the plate. Evenly illuminate the negative by means of the reflector outside the window-shutter. Rack out the camera, and move it along the support backwards and forwards until the image is sharp, and the marked portion of the focussing screen is occupied with the desired amount of the picture. If not as required, any alteration necessary should be made. When all is ready, the lens is closed and the dark-slide put into position. The exposure will depend upon the light, and again trial exposures are recommended by drawing the shutter so that a plate of fast speed may receive three distinct exposures of ten, fifteen and twenty seconds. The final exposure may then be made, and the other operations proceeded with.
As in enlarging, if a room cannot be had, the slides can be made in a reducing or lantern-slide camera, as Fig. 49, used in a reversed way.
The development is proceeded with exactly as lor plates. A developer giving strong contrasts is the best, as the one of hydroquin-one with caustic soda as the accelerator The development is carried on until the high lights begin to veil; aim at getting good density with thin high light and crisp detail. Judging the proper density requires some experience, as sometimes a slide which looks well in the hand does not throw a good picture in the lantern.
When the plate has been developed, fixed, washed and perfectly dried, it must be bound up with a piece of thin glass to form a cover and protect it from damage. Before binding, the slide should be made perfectly dry by gently warming.
A piece of lanternslide binding sufficiently long to go round all the four sides is damped. The slide and cover-glass (which must be quite clean) are put squarely together; place the edges upon the binding with gentle pressure when contact is made, turn on the next side, press, and repeat until all the four sides are covered. Now press down the overlapping portions of the binding on the opposite sides, and set aside to dry. The operation is more conveniently performed in a lantern-slide binding-clamp, Fig. 51, which holds the slide and cover-glass together while the binding is applied.
Masks of various shapes may be bought for placing between the slide and glass to render the appearance more effective. These masks are spotted to indicate the correct way of the slide. Each slide should be carefully titled.
The normal colour of the lantern slide is black and white - like a negative - except in some specially made lantern plates, which give a brown deposit. These latter may be toned in a combined toning and fixing bath to a purple tint. The ordinary ones may be treated with the same toning baths as given under the heading "Toning Bromide Papers," with practically the same resulting colours.