inch have been made. A well-equipped
photo-engraving establishment must have all these screens, and all of
them in many different sizes. In the writer's shop there are fifteen
cameras, all of them in constant use in the daytime and five or six of
them are always in use all night. Some days the bulk of the work in
the place will be a fine grade of magazine engraving calling for a 175
screen. In order to keep all the cameras at work all the time, a thing
that is very important in a well-regulated place, it is necessary to
have a number of 175 screens almost equal to the number of cameras.
The same is true of most of the other screens in general use.
Fortunately for the engraver and the consumer these screens
practically last forever if carefully handled.

The greatest developments in process work during the past few years
have been in the making of color plates. Beautiful results are
obtained in two colors by the "duograph" or "duotone" processes, the
plates being made for two printings. The three-color process aims to
reproduce all colors in three printings, by using inks of red, yellow,
and blue. This process is very interesting, but somewhat intricate.
Primarily, the results are made possible by color separations. The aim
is to take a colored subject--an oil painting, for instance--and by
photographing it three times, each time through a different colored
piece of glass, to divide all the colors into what are called the
three primary colors--red, yellow, and blue. From each of these color
separations a half-tone plate is made, and when these plates are put
on the printing-press, and the impressions are printed over each other
in yellow, red, and blue inks, respectively, the result is a printed
picture reproducing correctly all the colors of the original subject.

While many subjects may be reproduced accurately by this process, yet
the three-color process seems inadequate to give perfectly
satisfactory results in all cases. Nearly all three-color process
houses are now prepared to add a fourth, or key, plate, to be printed
in black, in case the subject seems to need it. The three-color
process has enabled many of the leading magazines to use illustrations
in colors, and there is not the slightest doubt but that there is a
great future for this class of work.

THE WAX PROCESS

By Robert D. Servoss.

Almost all of the maps found in text and reference books, as well as
the geometrical diagrams used in mathe