Screen for Making Photo-Mechanical Printing Plates.
Year: 1897

page_text: Date of Application, 12th Oct., 1897-Accepted, 20th Nov., 1897
COMPLETE SPECIFICATION.
Screen for Making Photo-Mechanical Printing Plates.
I, MAX LEVY of 1213 Race Street, in the City of Philadelphia County of
Philadelphia, and State of Pennsylvania, one of the United States of America,
Manufacturer of Engraved Gratings for the Half-Tone Process and Specialties
for Photo Engravers and Etchers, do hereby declare the nature of this invention
and in what manner the same is to be performed, to be particularly described and
ascertained in and by the following statement: —
This invention relates to photo-mechanical gratings or screens for producing
printing surfaces in carrying out the half-tone process; and it consists in a
different arrangement of the apertures of the screen by means of which it becomes
possible to make negatives as required for half-tone printing on gelatine dry-
plates, and of a quality and with a facility which it is impossible to obtain with
the aid of a screen as heretofore produced. In making a half-tone plate with the
aid of a screen what takes place is, that through each aperture in the screen is
formed a distinct image of the lens-aperture, and the half-tone negative consists
of a regular series of re-produced images of the lens-aperture. In order to develop
these images clearly it is necessary to resort to the use of vigorous intensifiers
which shall have the property of building up to the maximum opacity parts of
the image having a relatively weak deposit as developed. It will be obvious that
in an image of a square placed as above indicated formed through an aperture
in the ordinary cross-lined screen the corners of the image will fall behind the
sides of the aperture, and as the image is not formed at the point that would be
the real focus for the lens-aperture, regarding the screen aperture as a pin-hole
acting in the well-known manner of pin-hole photography, it follows that a large
portion of the light forming the image will fall behind the opaque line of the
screen, and that this portion of the image will be much weaker than the portion
formed by the light which has come directly through the aperture of the screen,
the developed image thus formed, notwithstanding that it is in form a full image
of the aperture in the lens, will have all its corners so weak as to show, but au
apparently round or octagonal image before intensification. At the same time
that the intensification develops these separate images by building up the weaker
parts in greater proportion than the denser ones, the effect of the entire picture
suffers material loss, as is well attested by all practical workers in this field.
With a screen having apertures arranged with their corners adjacent, it will
be apparent that with the same conditions as indicated as the most favourable
for the screen formed in cross-lines the separate images of the lens-aperture
formed through these apertures in the screen will lie directly in the direction of
the sides of these apertures, and that as a consequence any portion of the image
not of full strength will be equal on all sides and the images will fully overlap
each other exactly at the point where this overlapping is necessary to give the
effect of a dot in the high-light of the re-production, and for the same amount of
increase of size of image over screen aperture in this arrangement the maximum
excess would be but one half of what is required in the present screen.

page_text: apertures, the apertures alternating in the direction of their diagonals. The screen
shown in Figure 3 is made up of two plates Figures 3 and 3", one having vertical
rulings crossed at right angles by rulings of greater width than the rulings b
and the other plate has rulings dd both of which are of the same width as the
rulings and equally spaced. When the two plates are placed one upon the
other they will produce a screen or grating presenting a series of relatively large
obrong apertures arranged horizontally according to their greatest width and a second
series of smaller oblong apertures arranged vertically, the larger and smaller
apertures succeeding each other alternately in the direction of their diagonals.
In this, as in the other screens, the opaque blocks overlap each other.
In Figure 4 one of the plates is ruled with a comparatively fine line e which
is crossed by a much wider line e' to produce upon the plate Figure 4* oblong
blocks arrangel in vertical series according to their greatest length and in
Figure 4" the horizontal transparent lines are of greater width than the vertical
lines to present opaque blocks in horizontal series according to their greatest
width. When these two plates are placed one upon the other they will present
a screen in which there are relatively larger and smaller transparent squares suc-
ceeding each other alternately in the direction of their diagonals, the corners of
the oblong opaque blocks of the separate plates overlapping each other.
In Figure 5 there is shown a screen in which the plate Figure 5 is ruled with
cross lines ff through an opaque ground leaving opaque squares or blocks and
said squares are crossed diagonally by narrow rulings said rulings intersecting
the centre of the squares. The rulings upon the plate Figure 5" are similar,
presenting cross-lines and diagonal lines, but in this case the diagonal lines cross.
the opaque blocks to one side of their centre as shown; thereby presenting upon
the plate Figure 5 triangular opaque blocks of equal size, and upon the plate
Figure 5" triangular opaque blocks of different sizes. When these plates are
placed one upon the other they produce the screen shown in Figure 5 presenting
transparent squares and intermediate oblong apertures the ends of which are
formed by the overlapping corners of the opaque triangles.
Figure 6 is a modification of Figure 5 and in this case the plates Figure 6*
and Figure 6 which make up the screen are ruled with transparent lines upon
an opaque ground, the cross lines g g being of different width to first present
oblong blocks, and said blocks are crussed diagonally by thinner lines which
cross the centre of said blocks, as shown. In Figure 6 the oblong blocks are
arranged vertically to their greatest width and in Figure 6" said oblong blocks
are arranged horizontally. By this arrangement the two plates when placed
together present relatively larger and smaller blocks succeeding each other in the
direction of their diagonals, and between said transparent blocks, vertically and
horizontally, are formed oblong apertures positioned diagonally.
°
Screens constructed as herein shown and described obviate the objections apper-
taining to the printing surface wherein both the black and white dots are con-
nected by thin lines. With the improved screen the dots appear in their proper
size and are dis-connected to produce a superior printing surface and the screen
may be termed automatic as it does not depend to the same extent for successful
use upon the screen aperture.
Having now particularly described and ascertained the nature of my said
invention and in what manner the same is to be performed, I declare that what I
claim is:
1st. A grating or screen presenting transparent rectangular apertures on an
opaque ground, said apertures being positioned so that they succeed each other in
the direction of their corners, the opaque portions of the screen being formed of
larger blocks the corners of which overlap, substantially as shown.
2nd. A grating or screen made up to present a series of rectangular transparent
apertures adjacent to which are rectangular opaque portions the corners of which

page_text: overlie each other, substantially as shown, whereby a grating or screen is produced
having a less proportion of transparency than opacity.
3rd. A grating or screen made up of a pair of plates each having different
rulings so that when positioned one adjacent to the other the completed screen
will consist of transparent rectangular apertures on an opaque ground said apertures
succeeding each other in the direction of their diagonals, and opaque portions
formed of larger blocks the corners of which overlap.
4th. A grating or screen for the purpose set forth made up to present a series
of rectangular transparent apertures which succeed each other in the direction of
their diagonals and are separated by opaque blocks which also succeed each other
in the direction of their diagonals, each succeeding opaque portion being inter-
sected by a transparent line, substantially as shown.
5th. A grating or screen presenting opaque rectangular portions the corners of
which overlap said opaque portions being intersected or divided to provide trans
parent portions which are so arranged as to be alternately at right angles with
each other, and intermediate transparent rectangular portions which succeed each
other in the direction of their diagonals.
Dated this 11th day of October 1897
CRUIKSILANK & FAIRWEATHER,
Chartered Patent Agents,
62 Saint Vincent Street, Glasgow, Agents for the Applicant.