El Paso herald. (El Paso, Tex.) 1901-1931, 1912-09-09

embellish even the cheaper classes of
publications, including the daily news
papers. This came into general use in
the early COS and is being continually
improved With the increased number
of halftones and their improved quail
ity as used in the magazines, came
reduction in the use of wood engrav-
ings and other kinds of Illustrations
which had previously been in vogue.
Inc halftOne illustration through the
mechanical means of its construction is
necessarily true to the original sub
Ject- In that way, as in many others,
it is q long step in advance over earlier
methods of illustration which depended
entirely upon the skill of the hand.
With the improvement in quality also
came a great reduction in price, a full
page haftOne in a magazine costing
from a 10th to a fifth of the price of
a fairly good wood engraving. The
process of photOengraving includes
two branches the halftOne and the line
: engraving, which is known also as the
zinc etching.
How HaIftones Are Made.
The halftone process resulted from
experiments by Frederic J. Ives, Of
Philadelphia who made the discoveries
leading up to it when ne was in charge
of the Photographic laboratory of the
Cornell university in 1881. The name
of this branch of phOtOengraving is in
a way descriptive of the process, mas
much as it brings out by chemical and
mechanical methods the various gra-
dations of light and shade, or tone, of
the photograph or painting which is
the subject of reproduction
Ives conceived the idea Of breaking
up the surface of the picture into mi
mute dots and lines, which in that por-
ton to print dark should be heavier
than in the portions to be in the lighter
tones. This he accomplished by the in
vention 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,
hlnvn Al
mOnd point diagOnaly across its sur
face 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 looking through it is
OF series of cross lines with minute
transparent openings between them
This screen is inserted in the plate
holder of the camera used in process
sitized plate upon which the negative
is to. be made. The result is that a re-
production of the screen appears upon
the negative, as well as the picture
which is to be reproduced.
Screen Is Key TO Process.
If, for instance, landscape is the
subject for reproduction, the high light
effect would predominant in the sky
of the picture. and where the sEv an
pears in the photograph, because of
the density Of the light reflected from
it through the lens of the camera on
the sensitized plate, a halation occurs
around the light admitted through the
openings in the screen. so that the line
effect of il is destroyed and a series
of small dots will appear in the result
ing halftOne. COrrespondingly, in the
dark portion of the picture rejecting
but small amount Of light the line
OF the screen is reproduced or else
entirely lost In the resulting hslftone,
thus leaving a substantial and solid,
or nearly solid, surface in the resulting
printing plate. This screen is, as will
readily be observed, the key to the
process, for without it merely a pic
ture could be taken. that would have
no qualities from which satisfactory
etching could be done.
In order to adapt the process to vari-
GUS grades Of paper, the screens are
ruled with lines of varying coarseness,
running, for ordinary newspaper work,
from 65 to 100 lines TO the inch: for
ordinary supercalendered paper, about
40 lines to the inch; and for coated
paper, from 13S to 1f5 lines to the inch.
In the Photographic part OF the pro-
cess in both the halftOne and line
branches the negative that is made
from the copy is Of the wet plate va
riety now almost obsolete for any other
purpose 1t is used because of the
fact that the black parts of the copy
are reproduced in the negative in an
absolutely transparent line, whereas in
dry plate photography thin haze ap-
pears over the line, and to an extent
would interfere with perfect etching.
Etched on Copper.
After the negative has been made
from the copy under consideration, it
is coated with a solution of liquid rub
Der and collOdiOn. and after drying for
q few minutes il is placed in a bath
of acetic acid, which enables the work
man to remove the film, now trans
posed into a thin rubber membrane,
which is then transferred to a sheet of
plate glass usually about Is by is
inches in size, enough different mega
tives being placed upon this glass to
allow the workman to handle them in
a wholesale manner. After these neg
to the exact size of the rquired cut
they are ready for printing on the
sheet of metal upon which they are to
be etched
In the halftone process this metal
consists OF copper the surface OF which
has been coated with a sensitized solu-
ton. The negative is placed in a print
ing frame and the copper laid face
down upon it, and by action of sun
light or arc electric light a print is
made on the metal in practically the
same manner that the gallery pho
tOgrapher prints his negative upon the
sensitized paper.
After this print has been made it is
deyeloped bv certain Chemicals and
then by heat baked into the copper. The
plate now is ready for etching, and it
is at once immersed in a bath of ses-
quichloride of iron. The sensitized
surface of the copper, where hardened
by the action OF light shining through
the negative, has, by chemical action.
become imperviOus to the action of the
etching solution, whereas the parts not
affected by the light Immediately be-
gin to dissolve after being put in the
iron solution. Within six or seven min
utes a depth sufficient for ordinary
printing has been reached and the
plate is then taken out of the etching
bath, washed and dried and cut UP into
small pieces containing one or two
of the cuts.
These are distributed among finishers,
who reetch in certain portions where
more brilliancy is required, and with
q tool known as a burnisher manipu-
late the dark portions of the plate in
such a way as to bring out more near
ly, If required, the quality of the orig
inal copy. From these finishers the
plates go to the hand engraver, who
removes, with an engraver's tool. by
cutting into the copper, any black
spots or imperfectiOns which may have
occurred in the process.
After this has been done it remains
to nail the metal on a wooden block
so that the combined thickness OF the
metal and wood is .91S of an inch,
which is standard type high" in the
printing business.
No Screen In Line Process.
The branch of phOtoengraving re-
ferred to as line process, or zinc etch-
ing, differs from the halftOne method
in that no screen is used. BY this
method only COPY showing clearly def