Evening star., 1912-09-09

in both the halftone and line branches
the negative that is made
Wet Plate from the copy is Of the wet
n.l plate variety now almost
obsolete for any other pur-
pose. 1t is used because Of the fact that
the black parts Of the copy are repro
duced in the negative in an absolutely
transparent line. whereas in dry plate
photography thin haze appears over the
line. and to an extent would interfere
with perfect etching. After. the negative
sideration. it is coated with a solution Of
liquid rubber and collodion, and after dry
ing for few minutes it is placed in a
bath Of aretic acid, which enables the
workman to remove the film. now trans
posed into thin rubber membrane, which
is then transferred to a sheet of plate
glass usually about 15 by 1S inches in size,
enough different negatives being placed
upon this glass to allow the workman to
handle them in a wholesale manner.
After these negatives have been properly
squared up to the exact size of the re-
quired cut they are ready for printing
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 q sensi-
tized solution. The negative is placed in
printing frame and the copper laid face
down upon it, and by action of sunlight
or arc electric light a print is made on
the metal in practically the same manner
that the gallery photographer prints his
negative upon the sensitized paper
After this print has been made it is
developed by certain chemicals, and then
by heat baked into the
Plate Ready copper. The plate now is
for Etch;no ready for etching and 1t
A is at once immersed in a
bath of sesquichloride of iron. The SEN
sitized surface of the copper, where hard
ened by the action of light shining
through the negative, has. by chemical
action, became 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 minutes 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 two of the cuts.
These are distributed among finishers
who re-etch in certain portions where
more brilliancy is required, and with a
| tool known as a burnisher manipulate the
| dark portions of the plate in such a way
as to bring out more nearly, IL required,
the quality of the original copy. From
| these finishers the plates go to the hand
"
ers 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 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
The branch of photo-engraving referred
TO as line process, or zinc etching. differs
from the halftone method in that no
screen is used BY this method only copy
showing clearly definite lines. such as
wings. reproductions of type matter,
book plates. the copy for which was rem
dered in pen and ink. would furnish suit
able copy for line engraving. In this
process a negative is made from the orig
inal drawing and 1t is obvious that, be-
cause Of the lines appearing distinctly
without gradation of shades or color the
screen is not required.
The best grade Of halftone work al
ways is etched upon copper, whereas line
for the reason that zinc suff1ces for the
line process and has the advantage of be-
ing much cheaper metal.
X
The line engraving is naturally done in
the same manner as the halftone, ex-
cept as to detail. In
Line stead of etching in ses-
quichloride of iron the
Engraving. zinc plate. upon which
the line engraving has been printed, is
etched in nitric acid, that chemical being
better adapted to the etching of zinc
plates In line engraving 1t is neces-
sary to cut the spaces between
lines to q greater depth than has ap-