Evening star., 1912-09-09
By Frederic J. Haskin.

The development of the photo-engrav-
ing process, more than any other one
thing, has made possible the wonderful
illustrations which now embellish even
the cheaper classes Of publications, in
cluding the daily newspapers. This came
into general use in the early nineties and
is being continually improved. With the
increased number of halftones and
their improved quality as used in the
magazines came a reduction in the use
of wood engravings and other kinds of
illustrations which had previously been
in vogue The halftone illustration
through the mechanical means Of its
construction is necessarily true to the
original object In that way, as in many
others, it is a long step in advance over
earlier methods of illustration. which de-
pended entirely upon the skill of the
hand.
With the improvement in quality also
came a great reduction in price, full
page halftOne in a ma-ga zine costing
from tenth to fifth of the price of a
fairly good wood engraving. The process
of photo-engraving includes two branches
the halftone and the line engraving,
which is known also as the zinc etching.
The halftone process rehulted from
experiments by Frederick ]. Ives OF
P il a d phia, who
ExnerimentS made the discoveries
leading UP to it when
VI Z. .. AscS. he was in charge OF
the nbotocraphic laboratory of the Cor
nell University in 1881. The name OF TINS
branch of photo-engraving is in a way
descriptive of the process, inasmuch as 1t
brings out by chemical and mechanical
methods the various gradations Of light
and shade, or tone. of the photograph or
painting which is the subject of repro
duction. Ives conceived the idea or
breaking up the surface of the picture
into minute dots and lines. which in that
portion to print dark should be heavier
than in the portions to be in the i1ghter
tones This he accomplished by the in
yention Of the halftone screen.
This screen is of glass. there being
two pieces of plate glass folded over and
cemented together, each piece of glass,
however, having been ruled with dia-
mond point diagonally across it's surface
to a slight depth at intervals equal to
the thickness of the ruled lines. After
the surface of the plate has been ruled
as indicated the lines are filled In with
an Opaque substance, SO that when folded
together as stated, the effect upon look
ing through it Is of a series or cross
lines with minute transparent openings
between them. This screen Is inserted
in the plate holder of the camera used In
process work. Immediately in front OF the
sensitized plate upon which the negative
is to be made. The result is that re-
production of the screen appears upon
the negative, as well as the picture which
is to be reproduced.
IT, for instance, a landscape is the sub
ject for reproduction. the high light ef-
feet would predominate in the sky Of the
nicture. and where the sky appears in
the photograph. because Of the density
of the light reflected from 1t through the
lens of the camera on the sensitfzed
plate a halation occurs around the lght
admitted through rhe openings in the
screen, so that the line effect of 1t is
DESTROYED and a series of small dots will
apear in the resulting halftone. Cor
respondingly, in the dark portion of the
picture rejecting but a small amount of
light the line effect of the screen is re-
produced or else entirely lost in the re-
sulting halftone. thus leaving sub
stantial and solid. or nearly solid sur
face in the resulting printing plate This
I'screen is, as will readily be observed, the
key to the process, for without 1t merely
a picture could be taken. that would
have no qualities from which satisfactory
etching could be done. In order to adapt
the screens are ruled with lines of vary
ing coarseness, running, for ordinary
newspaper work. from 90 to 100 lines to
the inch: for ordinary superintendent
paper, about 100 lines to the inch. and
for coated paper. from 133 to 115 lines to
the inch.