room the plate goes to the "router," an ingenious machine,
with a cutting tool revolving at a speed of fourteen thousand
revolutions a minute, which quickly removes the waste metal in the
large open places between the lines and dots. The zinc plates are
carefully looked over by a finisher, defects are removed, and the
metal plates are then nailed on wooden blocks, so that they will be
"type-high," that is, of exactly the same height as the metal
type-forms used in printing. Hand presses are a necessity in all
photo-engraving shops, and with these several "proofs" of each plate
are printed in order that the customer may judge of the quality of the
plate.

While the line, or zinc etching process is immensely useful, in
reproducing pen-and-ink drawings, maps, wood-cut prints, etc., yet the
half-tone process is the one that practically revolutionized all known
methods of illustration, after it had become perfected. While zinc
etching is limited in its capabilities to the reproduction of black
and white subjects, practically everything in art or nature may be
reproduced by the half-tone process. The half-tone "screen" makes it
possible to take a photograph or wash drawing and break the flat
surface of the picture up into lines and dots, with the white spaces
between that are an absolute essential in relief plate printing. If a
half-tone print taken from any magazine or periodical is examined
closely, either with the naked eye or a magnifying glass, it will be
seen that the entire picture is a perfect network of lines and dots,
and that there are two sets of lines running diagonally across the
plate at right angles to each other. In the darker portions of the
picture it will be seen that the lines are very heavy, with a small
white dot in the centre of each square, made by the intersecting
lines. In the lighter portions of the picture, these lines will be
found to be very fine, while in the lightest parts, or in the "high
lights," as they are called, the lines disappear and in their places
are a mass of fine dots, not much larger than a pin point.

To make a half-tone plate of a photograph or other subject, it is
necessary to break the negative up into lines and dots. It is for this
purpose that the half-tone "screen" is used. The screen consists of
two thin pieces of plate-glass, on the surface of which a series of
very delicate parallel black lines have been ruled running diagonally
across the glass. When these pieces of