IMPROVEMENTS IN METHODS OF PRODUCING PRINTING BLOCKS BY MEANS OF PHOTOGRAPHY
Year: 1883

page_text: PROVISIONAL SPECIFICATION left by Walter Bentley Woodbury at the
Office of the Commissioners of Patents on the 5th October 1883.
WALTER BENTLEY WOODBURY, of South Norwood, in the County of Surrey
"IMPROVEMENTS IN METHODS OF PRODUCING PRINTING BLOCKS BY MEANS OF
PHOTOGRAPHY
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My invention relates to surface blocks by the aid of which typographic prints
may be obtained in the ordinary printing press, and it has for its objects novel
methods of giving to photographic negatives or positives the necessary qualities to
produce from them such surface printing blocks.
These qualities have usually been obtained by breaking up the continuous half
tone of the negative or positive produced in the ordinary way by photography, into
a series of lines, simple or crossed, dots, or grain similar to that produced by a
lithographic stone or by effects similar to net work or gauze. From negatives or
positives so produced printing blocks have heretofore been obtained either by
making reliefs in the well known way and pressing such reliefs into the surface of
metal, or by transferring to zinc and then etching, also by exposing negatives so
produced over a sheet of zinc covered with a substance having the property of
becoming insoluble by the action of light, such as bitumen, or gelatine and
bichromate of potash, and after removing the soluble parts etching the parts left
bare. These processes are and have been for some time in ordinary use, and my
invention consists in new or improved methods for the production of negatives or
positives suitable for the purposes above described.
In order to put my invention in operation, I procure a series of negatives or
positives from such objects as fine ruled lines, netting, gauze, dots, or a print from
a grained stone. I use these as "resists" from which I make in the ordinary way
what is well known as a carbon transparency and I transfer the same by the
ordinary method to the negative or positive and by them washing away the
soluble portions I give them the necessary qualities. Or, sometimes I make a
photo-lithographic transfer and I transfer the same to the negative or positive, and
if sufficient density is not obtained, I dust bronze or other opaque powders over
the image, so increasing it in force.
In another method which I sometimes adopt, by means of what is known as the
dusting process I coat a sheet of glass with a compound of gelatine or albumen,

page_text: grape sugar, and bichromate of potash, and after exposure under a negative or
positive I sift over it suitable granular powders, or the material used for flocking
paper, thus producing a grain negative or positive suitable for the purposes already
described, or I coat a negative or positive with the same solution and I treat it in
the same way as the plain glass.
Or sometimes by means of what is well known as the Woodbury process I make
a relief image from the combination of the negative or positive and any of the
various resists mentioned and by rolling or other convenient pressure I make a
reverse relief of the same in a sheet of enamelled or glazed cardboard, this image
I ink over carefully with an ink roller and I transfer in the ordinary way the
image so produced to zinc for etching or to stone for lithographing.
Or sometimes I take a gelatine relief developed on glass by the Woodbury
process in the usual way and having warmed the relief 1 pour over it melted wax,
paraffin, or similar suitable material, and on this I lay a sheet of plate glass,
previously greased and warmed and after squeezing out the superfluous wax I
allow it to cool. When set I detach the glass leaving a smooth and even surface of
wax filling up the hollows of the relief. Over the surface so prepared I pass
backward and forward a fine flexible and elastic V shaped tool in the same way as
in an ordinary planing machine, the tool cutting deeper or shallower lines according
to the depth of the wax; the same operation is then performed in a transverse
direction giving a series of cross lines varying in depth and thickness and from
this I take an electrotype from which I take a second one which forms the printing
matrix..