Improvements in Means for Producing Photo-mechanical Printing Surfaces.
Year: 1892

page_text: Date of Application, 1st Dec., 1892-Accepted, 19th Aug., 1893
COMPLETE SPECIFICATION.
Improvements in Means for Producing Photo-mechanical Printing
Surfaces.
I, Dr. ERNST VOGEL, of Charlottenburg, near Berlin, in the Empire of
Germany, Assistant at the Photochemical Laboratory of the Royal Technical
High School, 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 :-
The purpose of the process which forms the subject matter of the present
invention is to obtain colored pictures or reproductions of natural colors by the aid
of photographic printing processes and relates to the preparation of autotypes,
photolithographic, collotypes and other printing plates from metal for block
printing, chromolithography and chromozincography or working with other metals
(copper, brass, etc.,) as printing plates in which, by separating certain colors, and
by arranging a corresponding color-sensitiveness for each monochromatic print, the
photographic impression so takes place that by printing the monochromes one on
the other, a finished colored print is obtained.
"
As a rule three autotypes or other printing plates are sufficient; one for "blue
printing dye made from a negative taken on a plate not sensitive to blue but to red,
yellow and green rays; one for "red" made from a negative taken on a plate not
sensitive to red but generally sensitive to green rays; and one for "yellow" made
from a negative taken on a plate not sensitive to yellow, but generally to blue
rays.
The homogeneousness of the general effect in pictures produced in this way, and
the imparting of a natural and artistic expression to same, depends upon certain
conditions which must first be explained in the light of the present state of the art
before the characteristic principle of the new process, which fulfils these. conditions,
is demonstrated.
It has long been known how to obtain half-tones and transitions between light
and shade in photographic block printing and lithography, by means of placing an
opaque grating or net before the photographic plate during exposure or before the
positive when this is being copied (on paper or glass) from the corresponding
negative, such net being produced on a glass plate by engraving or photography.
By means of this net the light is prevented from working on the whole surface
of the plate, and in the points which remain under the net there are places which
copy dark or black.
The impression can be taken either behind a net plate or behind a line plate
which is turned 90° after half exposure (Meisenbach process). This is the generally
known old process of breaking the half tone of a negative to enable it to be treated
for etching and printing work, that is to make so called autotypes.
If two or three autotype-blocks or stones for different dyes for color printing are
made, it will be seen by printing them together, that there is formed a so-called
" moiré."
This "moiré antique" is very well known to manufacturers of autotypes, and
can easily be shown by putting together two net plates (gratings) or real nets with
the lines running in the same direction. To avoid this "moiré antique" it is
necessary to turn the net plates when making autotype blocks for printing together..
If only two blocks are required, same must be placed so that the lines of the two
nets are turned at an angle of 60 degrees to each other. For printing three auto-
type-blocks together the nets must be turned to angles of 30 degrees one to the
other.
If the turning is less than 30° "moiré antique" is formed. It is therefore

page_text: impossible to print more than three autotype-blocks. together, and it is difficult to
maintain the exact turning angle of 30°.
All these difficulties are entirely avoided by my process, which is as follows:-
The nature of the invention is such, that, for each plate, only one plain line
system is used, that is, there are no cross lines as in all autotypes, hitherto used,
this line system being turned to a certain angle for each of the succeeding
impressions or plates. This angle differs and depends upon the number of plates to
be printed together. For two plates an angle of 90°, for three plates an angle
of 60°, etc., would be the best.
Each photographic plate, therefore, only contains one line system with no inter-
secting lines. From this it follows that a net does not appear until the subsequent
printing from the lithographic or other plate copied from the autotypes, or printed
from the autotype plate itself.
The advantages of the new process are as follows:-
More than three plates can be printed together, even six being possible.
There is no danger of the formation of "moiré antique," because it is not
important, in printing together three of these line autotypes, to place them at an
exact angle of 60 degrees, some degrees more or less doing no damage, while, when
printing together three blocks with crossed lines, the angle of 30 degrees must be
exactly observed.
The working with single lines is therefore much more easy than with crossed
lines.
When printing together three net blocks (crossed line blocks) a star-shaped
figure is formed by the crossing of the six lines which spoils the print. This star-
shaped figure does not appear when printing together three single-line blocks.
The special mode of carrying out the new process is, that first a plate is prepared
for "blue" with red-yellow sensitized plates, the line plate being then placed before
the plate or the original. Then the second plate for "red" with a yellow-green
sensitized-plate is taken, the lines being first turned from 60 to 90 degrees.
Finally, the third plate for "yellow" is taken on a blue sensitized coating with
the lines turned at a different angle. If necessary a fourth plate can also of course
be taken. The process constituting the present invention, however, is altogether
independent from the mechanical means designed to carry it out; for instance, the
line plate can be outside as well as inside the camera, or before the positive or
behind the diapositive, or may be used in any other known way, for instance in the
printing frame, etc.
The lines can either be obtained photographically or mechanically, by guil-
loching the lines on the pigment print obtained by copying the original negative on
pigmented gelatine paper as in carbon process, or by Ive's process, or in any other
suitable known way.
The use of the photographic line-negatives for the block and stone surfaces in
block printing and lithography is known, and, therefore, needs no explanation.
Block printing and lithography in natural colors are obtained from the combined
line negatives, just as perfect as in the process of photolithography or zincography.
For transferring the line negatives on stone, zinc, or other metals, for the purpose
of etching or for allowing photo-lithographic or zincographic prints being taken
therefrom, the line-negatives may be copied directly on stone or zinc or other
metal, or they may be copied on transferro-type paper and transferred by the well
known transferro-type process.
Having now particularly described and ascertained the nature of this inven-
tion and in what manner the same is to be performed, I declare that what I
claim is :-
1. The use of a line plate in taking photographic negatives for color printing in
half tones (autotypy) and which is not turned for one and the same negative, as in
Meisenbach's and Albert's processes, but is only turned for each of the several
consecutive negatives prepared for different colors, so that each negative has only

page_text: one line system and not the autotypical net or reticule hitherto customary, sub-
stantially as described.
2. The method of obtaining lined autotype printing plates, in taking a transfer-
print from the original negative on lithographic stone and zinc, or any other metal
suitable for etching, by the process above mentioned and printing the particular
color required from the plates thus obtained, this method differing from present
methods in that, instead of net negatives, line negatives with different colors are
used, the angular position of the lines of same being only changed for each
consecutive plate, substantially as described.
3. The printing of the line blocks or stones made after the above mentioned
process.
1000
ALLISON BROS.,
Agents for the Applicant.