Aldis, M.A.
Cambridge: at the University Press 1916
can then be printed from in the same manner as a woodcut.
It is obvious that in printing from a relief block those portions
of the face of the block which come in contact with the paper
will produce corresponding solid marks on the paper,
whether they be lines, dots, or larger portions of the surface.
Since the marks thus made must be solid black, or one tone
of colour if a colored ink is used, tints and shades cannot be
rendered by this method; though the effect of them is
approximately attained in wood engraving by the use of lines
graduated in thickness and distance from each other so as to
produce the simulation of tint. The problem of reproducing
pictures composed of tints and light-and-shade (and not of
lines) was solved by the invention of the Half-tone process,
sometimes called Meisenbach process, now in general use for
photograph for transfer to the metal plate, a glass screen, closely ruled with fine lines at right angles to each other, is
interposed between the negative and the picture. The result of this is that the image on the negative is broken up into
small dots which vary in size and density according to the amount of light reflected through the ruled screen by the
different parts of the picture. The face of the plate and the resultant reproduction thus consist of a mass of minute
dots which are not separately visible to the eye but by their varying texture give the effect of the tones of the original.
This construction may readily be seen by examining one of these illustrations with a magnifying lens. In the lighter
parts of the picture it will be noticed that the dots are small and distinctly separated by the white ground between
them. In the middle tones the black and white are more nearly even, while in the shadows the texture becomes white
dots on a black ground. In some of the coarser work used in newspaper illustration this effect may be detected
without the aid of a lens.
In Photogravure and other intaglio processes it is the design itself that is exposed to the action of acid, and so is
bitten into the surface of the plate which is then printed from after the manner of an etching. Collotype and Heliotype
are printed from a flat surface and are akin to the process of lithography, the prints being made from a prepared
surface of gelatine instead of from a stone.
From the earliest days of book illustration the attraction of colored pictures has found its votaries. Copies of books in
which the illustrations have been colored are of common occurrence in all periods, and generally this addition is
contemporary work. Sometimes this was done by or for the owner, but in many cases books were issued by the
publisher with the illustrations either plain or colored. Initial letters printed in colour occur as early as Fust and
SchoetIer's Psalter of 1457; and in the Book of Bt Albans, printed at St Albans in 1486, the heraldic shields are printed
in colours. But until the eighteenth century little attempt was made to print illustrations in colors, and most of the
colouring was done by hand. .
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