By Emlyn M. Gill.
Practically all book illustrations, as well as those in catalogues and
periodicals of all kinds, are made by some method of photo-engraving.
Wood engraving is almost a thing of the past, and many who are in a
position to know predict that after the present generation of wood
engravers has passed out of existence, artistic wood engraving will be
a lost art. It is certain that there is now no younger school of wood
engravers growing up to take the place of the engravers whose work in
the leading magazines, up to a few years ago, made them famous.
The quickly made and comparatively inexpensive process plates have not
only taken the place of wood engraving, but have increased the field
of illustration to a very large extent. They have made possible
hundreds and even thousands of publications which could not have
existed in the old days of expensive wood engraving. The use of
photo-engraved plates has increased enormously each year during the
past twenty years, and with this increased use has come the inevitable
decrease in cost, so that illustrations are no longer much of a
luxury to the publisher.
Photography is the basis of all the mechanical processes that come
under the general head of photo-engraving. These processes are
generally called mechanical, yet, as in photography, great skill is
required to produce the best results. The higher grades of half-tone
work require much careful finishing, which is all done by hand, and
which, moreover, must be done by a skilful, intelligent, and artistic
engraver. Practically all things may be reproduced successfully by
photo-engraving, but the vast majority of subjects that go to the
photo-engraver are either photographs or drawings.
All methods of relief plate photo-engraving come under two general
heads: "Half-tone" and "line engraving," the latter being very
generally known as "zinc etching." Zinc etching is the simplest method
of photo-engraving and should be thoroughly understood before one
begins to inquire into the intricacies of the half-tone process. It is
used to reproduce what is known as "black and white" work, or line
drawings. Any drawing or print having black lines or dots on a white
background, without any middle shades, may be engraved by this
process. The old-fashioned "wet-plate" photography is used in making
practically all process plates, either in line or half-tone.
I will describe briefly all the operations gone through in making a
line plate, taking for a subject a map drawn in black ink on white
paper or a head drawn by Charles Dana Gibson,--subjects wide apart in
an artistic way, but of absolutely equal values so far as making the
plate is concerned. The drawing is first put on a copy board in front
of a camera made especially for this work, in whose holder the wet
plate has already been placed by the operator. The subject may be
enlarged or reduced to any desired size, nearly all drawings being
made much larger than they are desired to be reproduced in the plates.
The exposure is much longer than in ordinary dry plate work, generally
lasting in the neighborhood of five minutes. The result is a black and
white negative. That is, the lines that were black in the drawing are
absolutely clear and transparent in the negative, but the rest of the
negative is black. From the photographer, the negative goes to the
"negative-turning" room. Here the negative is coated with solutions of
collodion and rubber cement, which makes the film exceedingly
tough--so tough that it is easily stripped from the glass on which it
was made, and is "turned" with the positive side up on another sheet
of glass. If this were not done, the plate would be reversed in
printing--that is, a line of type would read from right to left, or
backward. After the negative is "turned," it is ready for the etching
room. Here the surface of a sheet of zinc about one-sixteenth of an
inch thick, which has been polished until it is as smooth as plate
glass and without a scratch or a flaw of any kind, is flowed with a
sensitized solution, easily affected by light. The negative is placed
in a printing frame over the sensitized zinc and a print is made. That
is, it is exposed to the sunlight or to a powerful electric light, and
the light shines through the transparent parts of the negative, and
hardens the sensitized surface; while the black part of the negative
protects the sensitized surface from the action of the light. The
plate is next "rolled up" with a lithograph roller which distributes a
thin coating of etching ink over the entire surface. The plate is then
washed off carefully by the operator, but the ink adheres to all
portions of the plate that have been acted upon by the light. We now
have a fully developed print on the highly polished surface of the
zinc that is an exact reproduction of the original drawing. It is now
necessary to make this print acid proof, and this is done by covering
the plate with a coating of very fine resinous powder, called
"dragon's blood," which adheres to the printed portions of the plate.
The plate is subjected to enough heat to melt this powder, and is then
ready for the acid bath.
A strong solution of nitric acid is used for etching zinc plates. This
acid is placed in trays, which are rocked constantly, either by power
or by hand, while the plate is being etched. The melted dragon's
blood makes a perfect acid resistant and the acid, therefore, does not
affect the print (or picture itself), but eats away the bare surfaces
of the metal between the black lines and the dots. When this etching
has proceeded far enough to make a plate that may be used in printing,
the lines and dots of the picture stand up in bold relief, while the
metal around these lines and dots has been eaten away to a
considerable depth.
There are many details that cannot be described in a short article,
but these are the principal operations gone through in etching the
plate. One very important detail in etching is to prevent
"undercutting." It is obvious that if the acid will eat down, it will
also eat sidewise. The acid resistant is only on the surface. If means
were not taken to prevent it, as soon as the acid got below the
surface, it would begin to eat in under the print and the lines and
dots of the picture would disappear; therefore, as soon as the plate
has had its first "bite," it is taken from the acid, dried, and
dragon's blood is brushed against the sides of the lines. This powder
is then melted and the plate given another etching. While the plate is
being etched down, it is removed from the acid several times, and the
sides of the dots and lines are again protected. After leaving the
etching 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 glass are placed together, face
to face, the parallel lines ruled on them intersect each other at
right angles, giving a very fine "mosquito-netting" effect. The method
of making the negative is very similar to that described in making
line negatives, excepting that in making a half-tone negative the
screen is placed in the plate-holder directly in front of the
negative. The subject is then photographed, and the result is a
negative completely covered with a mass of fine transparent lines and
dots.
Copper is generally used instead of zinc in making half-tone plates.
In making a print on copper the light shines through the transparent
lines and dots of the negative and hardens the sensitized surface of
the plate. The black parts of the negative between the transparent
lines and dots protect the sensitized surface. When the plate, after
printing, is placed under a water tap, the parts of the sensitized
surface that have not been acted upon by light wash away, leaving a
print that becomes acid proof after being subjected to an intense
heat.
The method of etching a copper plate is similar to that already
described for etching zinc plates, excepting that sesquichloride of
iron is used instead of nitric acid. In a half-tone the dots and lines
are so close together that great depth is neither desirable nor
possible, and no steps are taken to prevent undercutting.
The half-tone plate, after it has been carried as far as possible by
mechanical processes, is capable of great improvement in the hands of
skilful engravers. The plate as it comes from the etching bath may be
termed a mechanical product. Though great skill is necessary in making
the negative, the print, and the etching, the hand-finishing gives the
plate many of its artistic qualities. The unfinished plate is apt to
be more or less "flat" in appearance; the high lights may not be light
enough, while the dark portions of the plate are apt, in cases, to be
too light. The most common methods of finishing are reetching and
burnishing. The finisher dips a camel's-hair brush in acid and
applies it to the high-light portions of the plate, or other places
that are too dark, and allows it to act on the metal until these parts
of the plate are lightened sufficiently. The parts of the plate that
are too light are made darker by rubbing down the surface of the plate
with a tool called the burnisher. The skilful, artistic finisher has
other methods at his command of making the plate reproduce as
accurately and as artistically as possible the original drawing or
photograph. High lights are sometimes cut out entirely, or a fine
engraver's tool may be "run" between the lines; while a
"wood-engraved" finish is produced by cutting, in certain portions of
the plate, lines similar to those used in wood engraving.
In the price-cutting that has been going on as a result of the fierce
competition that has existed among photo-engravers during the past few
years, the artistic possibilities of the half-tone have been lost
sight of to a certain extent. The product of the engravers is sold by
the square inch, regardless of the fact that the cost of one plate may
be double the cost of another plate of the same size, but from a
different subject.
A point also worth remembering is that until the plate reaches the
finishers' hands, it has been more or less of a mechanical product;
and that the plate is made an artistic creation by the skill, care,
and brains of an intelligent class of men earning from $25 to $50 a
week. Those expecting "the best" at "the lowest price" can easily
guess about how much of this high-priced finishing they will get when
the price paid barely covers the cost of the mechanical product. Then,
engravers striving for high quality in the product pay from
twenty-five to fifty per cent higher wages, as a rule, than the cheap,
commercial shops. But the idea of square-inch price has so generally
permeated the buying public, that the larger and better shops have
been compelled, to a greater or less extent, to meet the prices of
their less skilful competitors. They are enabled to do this and give
their customers much greater value for their money, only through
better business methods, more modern facilities, and by conducting the
business on a very large scale.
The screens used in making half-tones represent an enormous outlay in
the large shops. A comparatively small screen costs in the
neighborhood of $100. A screen 18 x 20, ruled 120 or 133 lines to the
inch, costs about $500. Screens are made with different numbers of
lines to the inch, from 65, for coarse, newspaper work, up to 400. The
screens in general use are 65, 85, 100, 110, 120, 133, 150, 166, 175,
and 200; but intermediate sizes are also used, such as 125 and 140. A
screen containing 200 lines to the inch is about the finest ever used
for ordinary printing purposes, though a few screens with 250, 300,
and 400 lines to the 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.