Improvements in the Manufacture of Half Tone Gelatine Reliefs for Overlays for Process Blocks.
Year: 1893

page_text: Date of Application, 22nd June, 1893-Accepted, 4th Nov., 1893
Improvements in the Manufacture of Half Tone Gelatine Reliefs for
Overlays for Process Blocks.
I, JACOB HUSNIK, Professor in Vinohrady, Prague, Bohemia, do hereby
declare the nature of my said invention and in what manner the same is to be
performed, to be particularly described and ascertained in and by the following
statement :-
Many attempts have been made to supersede the ordinary plan of cutting out
the shadows from prints, and fixing them on the cylinder. This operation requires
considerable skill and experience on the part of the machine hand, and, while he is
thus working, the press or machine remains idle. I am also aware that gelatine
reliefs in half tones have been prepared, but they were made either by transfer, or
by the use of underlays of transparent gelatine, the light acting through this
layer of chromated gelatine. Reliefs of gelatine have also been prepared by the
glue-plate or gelatine type process, (such as described in my former Patent No. 37
of the year 1887) development taking place from the light side, without transfer.
But such reliefs have no half-tones, or differences in height. Only negatives in
lines and dots could be employed for this purpose, and, after development, the
lights having been deepened, the lines and dots remaining in the same plane.
Now the object of my invention is to manufacture half-tone reliefs without
transfer, developing from the front side, for the purpose of using them as overlays
for process blocks. These overlays are prepared directly by the action of light, in
a manner unattainable by hand.
My new method of manufacturing reliefs in half-tones (of which the lights vary
in proportion to the amount of light) consists in the exposure and development of
the chromated gelatine, from one and the same side, and in the same manner as in
the gelatine-type, and without transfer; but, so that, by means of the exposure
under half-negatives, as well as of negatives in lines and dots; the result in every
case is a relief of graduated heights or thicknesses.
The development is produced in a similar manner to that employed in the
gelatine-type, viz. by rubbing the plate with a brush, cold or warm. The
difference consists in the strength of the solution which is used in rendering
the chromated layer sensible. In my process I use 40 to 60 parts of water to one
part of salt of chrome; the object being to allow the light to penetrate the entire
layer of gelatine, of whatever thickness it may be, when exposed. The light acts
to the bottom of the layer, but it is not allowed to render it absolutely insoluble,
as it remains somewhat soluble in every part exactly in proportion to the strength
of the light, to the action of which it is exposed.
In case of a chromo-gelatine being copied under a negative, in lines and dots
(such as a pen and ink drawing, autotype, woodcut, and reproductions in lines
and dots) the fine lines are dissolved quicker than the masses of shade, the result
being a relief in half tones, and not in the ordinary lines and dots of uniform
depth.
When such copies are required to be developed cold, I use the well known liquids
for dissolving gelatine, when cold; as, for instance, solutions of bichromates :
chloride of zinc acetic or formic acid, and the like. In producing warm
development, I use only a brush and tepid water.
Preferably, and as an example, I take 10 lbs. of soft gelatine, or gelatine glue:
3 lbs. of glycerine: 2 lbs. of alcohol, and 35 lbs. of water. As soon as the gelatine
is softened in the glycerine and alcohol, it is dissolved in the water, then filtered,
and poured out on sheets of paper, laid upon horizontal plates of glass.
These

page_text: gelatine sheets soon become sufficiently hard, and are then hung up, so as to become
completely dry.
The gelatine paper can be sensitised (preferably) by using a bath consisting of
one part of bichromate of calcium dissolved in 40 to 60 parts of water, as
required; hard gelatine requiring more water than soft gelatine. The bath is
then neutralised with caustic ammonia. The prepared paper is then dried in
a dark place, and may be used under negatives either in half-tone, or in lines
and dots, or autotypes, and developed with a brush and tepid water, or cold, as
above described.
The depth of the relief being dependent only upon the thickness of the layer
of the gelatine which has been deposited or poured out upon the paper, it is
evident that such reliefs may be used in Woodburytype and in the production of
lithophanes but not as printing blocks in book printing, in consequence of their
being half-tone reliefs.
The half-tone gelatine reliefs hitherto obtained by transfer, are readily loosened
from the ground sheet, by peeling them therefrom with a knife, and they do not
retain any part of the paper. But, with my improved process, this result is
impossible; and this is an essential feature of my invention.
When my reliefs are prepared under negatives formed with lines and dots or
autotypes, they are characterised also by the lines on the highest places of the
relief being sharpest, the lines of the lower parts being weaker, according to
depth, until they disappear entirely. In ordinary reliefs produced by transfer,
these lines come out with equal sharpness in all gradations. In cases when the
exposed parts are reversed, the opposite result is obtained with transfer reliefs,
the highest parts having the least sharpness, and the lowest the greatest sharpness.
A similar result taking place with autotypes having heavily formed lines.
Another method of carrying out my invention consists in the use of paper
rendered transparent by means of varnish, which I afterwards cover with gelatine,
and expose it, negatively, on the reverse side, that is to say, the paper side; after
which the reliefs are developed by the solution of the gelatine.
Transfer being unnecessary with my invention, the process is considerably
simplified, and my reliefs are produced in a shorter time and less expensively than
heretofore.
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 :-
process
The manufacture and use of half tone gelatine reliefs, for overlays for
blocks; the reliefs being obtained by developing gelatine layers from the light side
without transfer; the gelatine being undetachably united to the paper or other
material, substantially as and for the purposes herein before described.
Dated 22nd June 1902
GEO.
DOWNING,
8, Quality Court, London, W.C., Agent.