Illumination and Its Development in the Present Day

by Sidney Farnsworth

For drawings executed in tone, the other method, known as the half-tone process, is used. In this case the drawing is photographed with a glass screen in front of the negative. This screen is ruled with fine lines in such a manner that the tints of the original are broken up into dots. The print is obtained on the metal, and the block is made in a somewhat similar manner to that of a line block. In etching, the metal is bitten away round the edges of the various dots more or less, according to the strength of these. This gives a similar effect of light and shade to the original. An examination, with a magnifying-glass, of any reproduction of a photograph or tone-drawing in any of the magazines of the present day will show this quite plainly.

When working for this process, drawings should be rather more vigorous than are required in the finished production. The reason for this is that the photograph generally softens down everything, so it is as well to forestall this by making the original stronger.

It is also important that the half-tones in the drawing should not tend towards being a bluish grey, as blue does not photograph well. The result of a reproduction from a drawing of this kind would be that the half-tones would be much weaker than in the original.

In colour reproduction, a method largely used is that known as the three-colour process. This is a development of the half-tone process. In this case, however, the drawing is photographed three times in succession on different plates. In each case a colour filter is placed in front of the lens, which allows only the red, yellow, or blue rays to pass through. By this means the three negatives obtained are records of the red, yellow, and blue used in the drawing. Three blocks are made, and are printed in red, yellow, and blue ink respectively, superimposed over each other. This, if carefully done, gives a fairly faithful reproduction of the original. Sometimes an extra block is used, and in the case of the reproduction of illuminated work, a special block is used to print the gold. It can easily be understood why this is necessary, as, when printed from the three blocks only, this comes out as a colour in the printing.

When working for this form of reproduction there is no need to limit oneself in the number of colours used. Work that has been executed with about twenty different colours can be reproduced as easily as that in which only four or five colours are used.

As in half-tone, the work should be stronger and more vigorous than is needed in the finished reproduction. The colours also should be bright and clear, and the modelling should be strongly accentuated, as this process has a tendency towards flattening everything. If the original appears flat and washed-out in treatment, it will certainly look much worse when reproduced.

Another process, largely used for commercial work, is lithography. This is quite different from any of the previously mentioned processes. In all these the blocks are in relief, and are printed in a typographic press. For the general form of lithography, a species of limestone is used. This process depends on the absorption of grease by this stone, and on the mutual antipathy of grease and water. The design is drawn on the surface of the stone with a greasy ink. The grease is absorbed by the stone. The stone is then damped all over; the greasy ink of the design repels the water, but where there is no design the surface of the stone becomes wet. An ink-roller is then passed over the stone while it is still damp. As this printing ink is of a greasy nature, it will leave the roller only for the lines of the design, which remain quite dry. The moist surface of the stone repels the ink. After the stone has been inked up, a print is obtained in a lithographic press.

For general work the surface of the stone is highly polished, but for the reproduction of chalk drawings and for shading purposes it is given a grain.

Zinc and aluminium plates are often used as substitutes for stone. These, although not as good as stone, have the advantages of being cheaper and more portable.

Colour printing by this process is known as chromo-lithography. A separate stone is used to print each colour. A careful tracing is first made of the outline of the drawing, and this is transferred to the surface of the stone. This forms the key-stone from which the other colour stones are prepared. When it is desired to print gold, the stone is rolled up with a very sticky kind of ink. A print is obtained in this medium, and while this is still tacky it is dusted over with powdered bronze, which adheres to the print and gives the effect of gilding to some extent. For very special work real gold is occasionally employed instead of bronze powder.