Improved Screen and Printing Surface for Use in Photo-mechanical Printing Processes.
Year: 1894

page_text: Date of Application, 19th June, 1894--Accepted, 21st July, 1894
COMPLETE SPECIFICATION.
Improved Screen and Printing Surface for Use in Photo-mechanical
Printing Processes.
I, MAX LEVY, of No. 1213 Race Street, Philadelphia, in the County of
Philadelphia, and State of Pennsylvania, United States of America, Manufacturer
of Specialities for Photo-engravers, 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 engraving in half-tone, the object
being to provide photo-mechanical half-tone printing surface having a different
texture from that produced by the means in current use, and at the same time
render more accurate the definitions of the details of the subject and a greater
variety of gradations of light and shade.
In all the methods which are at present in use of producing half-tone printing
surfaces by means of a lined or cross-lined screen the texture consists of a series of
subdivisions of the surface which while the individual elements of the series differ
from each other are still geometrically alike; that is, for any particular shade
there would be dots, lines or cross-lines which have the same geometrical relation
to each other whatever their individual character, and the same is true of all the
shades.
This invention consists in an improvement by means of which each subdivision of
the printing surface and the resulting texture of the printed impression consists of
regularly disposed groups of dots, fines and stipples, and the individual members
of each group are different from each other, but the groups are in their geometrical
arrangement similar throughout the series.
In order to carry out my invention it is necessary to have a screen or grating
which will have transparent apertures of different sizes arranged in groups, and
also opaque obstructions to the light differing in value from each other and also
arranged in groups. These groups may each consist of two, three, four or more
individual members, and the chief condition is that both transparent and opaque
members should differ in size from each other.
Such a screen may be formned of lines alternately thick and thin and crossed at
or nearly at right angles and in this case one of the sets of lines in each direction
must be displaced from the middle of the space formed by the complementary set
of lines, so as to form four transparent apertures varying in size, and the inter-
sections of the thinner and thicker lines will form the necessary opaque obstructions,
which also vary in size. Figure 1 shows a grating or screen of this construction,
and A and a designate a series of two sets of parallel opaque lines alternately
thinner and thicker, and A' a' a similar series of two sets of parallel opaque lines
but are somewhat further apart than the set A a. This arrangement will give a
different sized obstruction to the light; first, the intersections of the lines A and A',
second the intersections of the lines A. and a' and A' and a, and third the inter-
sections of the lines a and a'. The interval B will be smaller than B' and the
interval the same size as b, which will result in four different size transparent
apertures.
The screen may also be formed by having a series of parallel lines alternately
thinner and thicker crossed by a single series of parallel lines, as shown in Fig. 2.
This arrangement affords two different size transparent apertures Band 6 and two
different opaque obstructions formed by the intersections of the lines A and A' and
of the lines A' and a.

page_text: Fig. 3 shows a screen which consists of four sets of parallel lines crossing in
different directions, two sets crossed at right angles to each other and the other
two sets also crossed at right angles to each other and at an angle of forty-
five degrees to the first two sets, the spacing coinciding exactly to the relation
between the sides and hypotenuse of a right angled triangle, but the intersections
are so disposed that the resulting apertures shall vary in size, and in this ease
there will be two different size obstructions to the fight, formed first by the
intersections of the two lines A and a, and second of these same two and a a' added
thereto.
Fig. 4 is a view showing the texture of the resulting picture or printing
Eurface.
The screens here described are used in the same manner as the ordinary cross-
lined screen, and from such a screen the resulting picture will have in the highest
lights dots representing only the largest opaque obstruction in each group while in
a shade darker there will be added a smaller dot representing the next size inter-
section, and so on if there are more sizes. The same is true in the shadows-as
these become darker the light admitted by the smaller apertures will be ineffectual
to form a printing dot, and these will disappear in series as the shadows deepen
until the deepest shadows before the solid black surface will have only dots
representing the largest size apertures. This will greatly facilitate the reproduction
of fine detail, and by reason of the resulting variety of textures produce a far
greater variety of tones than can be obtained by the means at present in use and
which give the possibility of only one gradation of dot in the shadows.
The resulting picture produced by means of the screens described will have the
following characteristics: In the highest light, not pure white, there will be a
series of fine black dots which will correspond with the boldest intersections in the
screen as the shade becomes darker these dots will become slightly larger, and in
the lighter middle tints there will be present a second series of smaller black dots
corresponding with the lesser intersections of the black lines in the screen. These
two series of dots will increase in size as the shade deepens until they form con-
tinuous lines spaced similar to the corresponding lines in the screen. As the
shade becomes still deeper the dots represented by the smallest apertures in the
screen will disappear, and as the shades become deeper and deeper from this point
on the dots successively represented by the decreasing size transparent apertures
in the screen will successively disappear until in the deepest shadow which is not
black there will be but one white dot in each group, and this dot will represent the
largest transparent aperture in each group of the screen.
Having now particularly described and ascertained the nature of my said inven
tion, and in what manner the same is to be performed, I declare that what 1
claim is:
1. A grating or screen for the purpose set forth, which consists of parallel lines
of varying thickness and distance apart and crossed so as to form transparent
apertures of varying sizes arranged in groups.
2. In
a grating or screen for the purpose set forth, the combination, of
alternately thinner and thicker linea spaced at alternately greater and less distance
apart and crossed by a similar series of lines similarly placed.
3. A grating or screen for the purpose set forth, the combination, of alternately
thinner and thicker parallel lines spaced at alternately greater and less distance
apart and crossed by a single set of imiform parallel lines.
4. In a grating or screen for the purpose set forth, the combination with two sets
of lines crossed at right angles with each other, of two other sets of lines crossing
the first two sets diagonally at regular intervals forming different size transparent
apertures arranged in groups.
5. In a grating or screen for the purpose set forth, the combination with two sets
of lines crossed at right angles with each other, of two other sets of lines crossing

page_text: the first two sets diagonally at regular intervals, forming at their intersections
different size obstructions arranged in groups.
6. A photo-mechanical half-tone printing surface the subdivisions of which
consist of regularly disposed groups of dots the individual members of each group
differing from each other.
Dated this 1st day of June 1894.
CRUIKSHANK & FAIRWEATHER,
62, St. Vincent Street, Glasgow, Agents.