The first requirement will be a proof, on fine white paper, from a machine-ruled plate, or a plate with fine dots or stipple; a favorite being plates ruled diagonally and straight, either in single lines or crossed. These plates must be of good size, say 18 by 15, ruled with lines as fine as possible, 100 or 150 to the inch. The ruled sheet must be perfect, as any defect in it will be fatal.
Such a proof being secured, it should be carefully mounted with starch paste upon a stout piece of smooth cardboard, and should be carefully shielded from all chances of being soiled, as the slightest stain or mark upon it will unfit it for use. As such a fine line is very difficult to focus, especially in making the smaller screens, it will be found a good plan to cut four narrow strips of good, bold type, and paste these at the four corners of the sheet, just outside the ruling; these slips of type will be easy to focus, and will render the task of making the screens easier.
Plates ruled with single lines, either diagonally or horizontally, may be used instead of the cross ruling, and are by many preferred.
Those in possession of a ruling machine may make these ruled sheets by ruling a large litho stone, and pulling impressions from that stone. If this is done once, and done well, the sheets will last a lifetime; and if the stone be sufficiently large, and the lines very fine, the screens may be used for blocks 15 by 12 inches or larger.
To copy this ruled sheet, remove the mirror from the lens, and put the lens in the camera in its ordinary position; then pin up the sheet on the easel, and, after seeing that the easel and camera are quite parallel, proceed to make a series of negatives from the sheet, making screens of various degrees of fineness, varying from a coarse grain for a coarse photograph, to the finest possible for {66} photographs full of delicate half-tone, and from three inches to ten inches wide. Many subjects will need screens made especially for them. The screens must be free from speck or stain, and should be made upon very thin glass.
The nitrate bath should be in good condition, and the collodion ripe. Such negatives take a good deal of time making, but as they are the foundation of the process, and with care will last for years, the trouble must not be grudged.
The screen negatives being made, they must be varnished with a good, hard, well-filtered varnish, applied in a room quite free from dust.
The screens must be made by the wet collodion process. The ordinary gelatine dry-plate is utterly useless for such work. Gelatino-chloride plates might do, but the exposure is so very long that there is risk of shaking the camera during exposure.
THE GRAINED NEGATIVE.
For the first method a good vigorous photograph is selected, placed in position on a copying board, and the camera adjusted so as to get the image on the focussing screen the size wanted the mirror being used, as the negative must be reversed.