Improvements in Printers' Overlays and Process of Making the same.
Year: 1899

page_text: Date of Application, 3rd Oct., 1899-Accepted, 20th Jan., 1900
COMPLETE SPECIFICATION.
Improvements in Printers' Overlays and Process of Making the same.
We, EDWARD BIERSTADT, of No. 94, Reade Street, in the City of New York,
United States of America, Printer, and THEODORE BROCKBANK DE VINNE, of No.
12, Lafayette Place, in the City of New York, United States of America, Printer,
do hereby declare the nature of the said 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 a new process of making printers' overlays, and to
the novel overlays thus produced.
In printing pictures such as wood-cuts, photo-engravings, and other relief plate
illustrations, such as are usually printed on typographical presses, it has been
found necessary for good results, to employ for each picture a pad known as an
"overlay," which is applied to the tympan sheet facing the relief plate to be
printed. Such overlays are usually made by pasting pieces of paper over those
parts of the impression where the pressure is insufficient, until the thickness
becomes sufficient to so increase the pressure on these parts as to take up the ink
required to produce the desired effect, the necessary gradations of tone being
attained by bevelling off the surface. The preparation of these overlays requires
much time and skill. An ideal overlay is one the thickness of which is greatest
opposite the blackest portions of the picture, and least opposite the high lights,
and is graded proportionately through the range of intermediate tones.
To this
The object of this invention is to lessen the expense, and produce as nearly as
possible an ideal overlay, by a process involving no extraordinary skill.
end, we resort to photography, availing ourselves of the well known action of
light on bichromated gelatine. By our process we produce a photographic picture
of homogeneous composition, and of varying degrees of thickness, which can be
placed against the relief plate or engraving in the proper position, and thus form
a perfect substitute for the usual overlay.
By our process we preferably proceed as follows:-
We first prepare a solution of bichromated gelatine; the proportions may vary
with the quality of the gelatine, but ordinarily we employ about 50 gramines of
gelatine, 10 grammes bichromate of potash, and 40 cubic centimeters of water.
Heat these until dissolved, and then filter and pour on a piece of glass placed
exactly level to the depth of nearly two millimeters, and when the gelatine has
set, it may be placed upright to dry. These operations may be performed at any
time in advance of using, and must be done in the dark room.
When ready to prepare an overlay for any given engraving, we first print a
proof or impression of the engraving on a thin sheet of celluloid or thin trans-
lucent paper; this may be retouched or strengthened if desired. We then place
this print upon the gelatinized plate in a photo printing frame, and expose it to
the light in the ordinary manner of photo printing; after eight or ten minutes
it may be examined, and if all the details of the picture are visible, it may then
be removed. The gelatinized plate is then immersed in cold water to swell the

page_text: gelatine; after about ten minutes, or as soon as it presents sufficient relief, we
remove it from the water, dry the surface with blotting paper, and make a cast or
matrix of the swelled surface in plaster of paris.
We now take a thin sheet of gutta percha, which may vary for example from
one to five millimeters in thickness, and which preferably has been previously
attached to the surface of paper or thin cloth. This gutta-percha we heat gently
to soften it, and press it in contact with the plaster matrix in any suitable press.
The pressure must be sufficient to cause the soft gutta-percha to adapt itself to
all the variations in thickness of the matrix. After the gutta-percha has become
cool, the paper being dry, we detach it from the matrix.
The gutta-percha sheet thus formed is found to vary in thickness in proportion
or approximately so to the variations in depth of tone or shade in the print, the
lighter portions of the print appearing as the thinner portions of the sheet, and
the darker portions of the print being found as the thicker portions of the sheet,
so that the sheet of gutta-percha has all the requisites of an overlay. The varia-
tions in thickness should be exactly such as are required in an overlay to give
the best results in the printing.
The photo overlay thus produced constitutes a new product. It is distinguished
from the overlays heretofore made, in that it is homogeneous instead of being
built up of successive layers as heretofore.
The accompanying drawing indicates approximately the successive stages of
the operation just described.
Fig. 1 is a cross-section of a printing plate or cut, a being its printing face,
and its wooden base or mounting;
Fig. 2 is a section showing in opposition to Fig. 1 the paper e to be printed
on, and the overlay d behind the paper, the variations in thickness of the overlay
being here greatly exaggerated;
Fig. 3 is a sectional view of the gelatine plate e after it has been photo exposed
and subsequently swelled, the variations in thickness being similarly exaggerated.
Fig. 4 is a section of the plaster matrix f made from the swelled gelatine
plate e of Fig. 3.
Fig. 5 is a cross-section showing the gutta-percha sheet & pressed into the
plaster matrix so as to conform to the variations of thickness thereof, this gutta-
percha sheet being the photo overlay d of Fig. 2;
Instead of gutta-percha, we may use other materials as for example paper
mache or other homogeneous plastic materials, but we find gutta-percha to be
preferable.
For the matrix f, instead of plaster of paris, we may use a mixture of wax,
spermaceti and asphaltum or rosin, but in this case some material must be used
for the photo overlay d that will require no heat, or not enough to impair the
matrix.
By a modification of our process, instead of exposing bichromated gelatine to
light under a positive print of the picture and then swelling it, we may by a
reversal of this operation prepare a negative from the print and expose the
bichromated gelatine under this negative, and then dissolve away from the back
or reverse side of the sheet of gelatine those portions which being least affected
by light are most soluble, until the desired degree of relief has been obtained.
The gelatine sheet thus obtained can be dried and a matrix can be made from it,
and overlays of gutta percha or other material can be made in this matrix, as
before described.
In practicing our invention according to this method, we may proceed as
follows: First make a negative by placing the celluloid or transparent print in
contact with a photographic dry plate, exposed for a few seconds to a weak light,
then develop the negative as usual, fix and dry; and it is ready for the next
operation. For this we prepare in advance a tissue consisting of paper with a
thick coat of gelatine, say from one to five millimetres in thickness, containing a
little pigment, or even without any. This tissue can be prepared in advance and

page_text: will keep indefinitely; when required for use it must be sensitized by immersing
it in a three per cent solution of bichromate of potash and dried in the dark;
when dry we place it in contact with the negative and expose to light, and when it
has been sufficiently impressed it is placed in water for a minute or two; when
it stretches out flat place it face down on a piece of glass, squeeze out all water
until it shows a perfect contact free from air bells, lay it between sheets of paper
under pressure for fifteen minutes or more, then place it in warm water until the
gelatine softens sufficiently to permit the removal of the paper so that it will
leave the gelatine tissue on the glass; now gradually increase the temperature of
the water and rinse the surface of the glass until all the surplus of the gelatine,
not affected by light, is dissolved and washed off; then dry the plate spon-
taneously; when dry paste over the entire surface a sheet of smooth paper,
avoiding air bubbles, and allow this to dry, then detach it from the glass and the
operation is complete. From the gelatine sheet of varying thickness thus pro-
duced there can be made a matrix, and overlays of gutta percha or other material
can be made from this matrix, as before described.
By whatever method we operate, we produce photographically a print or
impression of the picture, which instead of being expressed in varying degrees of
shade or color like ordinary photographs, is expressed in varying degrees of
thickness.
Our process may be modified in many ways without departing from our inven-
tion, which includes any mode of producing a gutta percha or a moulded overlay
by developing from a print, engraving or relief plate, a photograph the variations
in the depth of tone or shade of which shall be represented by variations in
thickness, the differences of thickness being in such proportion as is required by
printers in making a practical overlay.
Our invention is not necessarily limited to producing the varying thickness of
the overlay by photographic means, as such variations in thickness might be
otherwise produced, provided the overlay shall be of homogeneous material, and
present the required variations in thickness.
Tissues may be prepared in advance by coating glass or similar plates with the
dissolved gelatine to which about 5 grammes of glycerine has been added to a
depth of about two millimeters, and the proportions being approximately as
follows: 50 grammes of gelatine, 40 cubic centimeters of water, and 5 grammes
of glycerine, and without using any bichromate of potash, and then drying and
stripping the gelatinous tissues from the plates and storing away these tissues
for future use. Such tissues will be flexible and durable, but when required for
use they must be sensitized by immersing them in a three per cent solution of
bichromate of potash for two or three minutes, and drying them in the dark,
whereupon they can be exposed, as before described.
Having now particularly described and ascertained the nature of our said
invention, and in what manner the same is to be performed, we declare that what
we claim is:-
1. The described printers' overlay consisting of a sheet of homogeneous moulded
material corresponding to a relief plate to be printed from, said sheet varying in
thickness in different parts in approximate proportion to the variations in depth
of tone in the picture to be printed.
2. The described photo overlay for use in printing from a relief plate, con-
sisting of a gutta percha or moulded photograph of the picture to be printed,
which varies in thickness in proportion to the variations in depth of tone in such
picture.
3. The described process of preparing a printers' overlay for printing from a
relief plate, which consists in photo exposing a sheet of sensitized gelatine beneath
a positive or negative print corresponding to the impression from such relief
plate, and subsequently treating the exposed gelatine with water to develop
variations in thickness therein corresponding to the variations in depth of tone

page_text: in the pictures to be printed from said relief plate, and forming from such
gelatine a gutta percha or moulded overlay.
4. The described process of preparing a printers' overlay, which consists in
exposing a sheet of sensitized gelatine beneath a positive print corresponding to
the picture printed from the relief plate, then soaking the gelatine in water to
swell the soluble portions thereof and thereby develop differences in thickness,
then preparing a matrix from such swelled gelatine, and forming in such matrix
an overlay duplicating the variations in thickness of said swelled gelatine.
5. The described process of preparing gelatine plates for making printers' over-
lays, which consists in adding glycerine to the gelatine, forming tissues thereof
without using bichromate of potash, drying and storing said tissues, and sub-
sequently sensitizing them by immersion in a three per cent solution of bi-
chromate of potash, and drying them prior to exposure.
Dated this 3rd day of October 1899.
J. C. MEWBURN & ELLIS,
55 & 56, Chancery Lane, London,
Chartered Patent Agents.