In- PROVEMENTS IN THE PRODUCTION OF NEGATIVES APPLICABLE FOR PHOTOGRAPHIC PRINTING, AND OBTAINING RAISED PRINTING SURFACES
Year: 1869

page_text: PROVISIONAL SPECIFICATION left by John Vincent Robinson at the
Office of the Commissioners of Patents, with his Petition, on the
20th March 1869.
I, JOHN VINCENT ROBINSON, of the City of Dublin, Ireland, Photo-
grapher, do hereby declare the nature of the said Invention for "In-
PROVEMENTS IN THE PRODUCTION OF NEGATIVES APPLICABLE FOR PHOTOGRAPHIC
PRINTING, AND
OBTAINING RAISED PRINTING SURFACES," to be as
follows:-
The first part of my Invention relates to the production of negatives
for photographic printing which I effect in the following manner :-Upon
a plate of glass or other transparent material I deposit or affix a layer
or stratum of suitable metal (preferably of silver) or metallic alloy, or
it may be a preparation of aniline or other suitable matter upon which
metallic or other surface a drawing may be made with pen or pencil.
The lines of the drawing or design are then removed by means of a
graver, etching needle, or other suitable instrument, or the drawing or
design may be at once etched in without the aid of the first pen or
pencil sketch if desired. A plate is thus obtained from which the
metal is removed in the parts representing lines in the drawing or

page_text: subject so as to admit light through the plate at those parts, and obstruct-
ing it wherever the metal deposit remains, thus producing what I term
an etched negative. A print may now be obtained from the negative
by placing it over an ordinary piece of sensitive photographic paper and
exposing to light in the usual manner, or by any of the usual methods of
photographic printing.
The second part of my Invention relates to the production of raised
surfaces for printing purposes by means of the same etched negative
obtained in the manner above described. To effect this I coat a plate
of glass or metal, or it may be a stone or other suitable material, with a
layer of gelatine, gum, or other suitable substance, to which has been
added a bichromate such as bichromate of potash or ammonia, or a
mixture of said bichromates for the purpose of rendering sensitive to light
the layer of gelatine, gum, or other substance employed.
The negative before described is placed in contact with the prepared
gelatine or other surface and is exposed to light, which light acting on the
film of gelatine through the lines of the etched negative hardens and
renders insoluble in water the parts of the gelatine or other surface so
acted on. The other parts of the gelatine film which have been pro-
tected from the action of light by the metal deposit on the negative
remains soluble. After thus exposing the gelatine plate to light I place
it in warm water which dissolves the gelatine in those parts not acted
on by the light, leaving a picture in relief corresponding to the lines
and marks of the etched negative, thus forming a raised printing sur-
face. From this raised surface a print can be taken by any of the usual
inethods of block printing, or a transfer can be made on to stone, but
I prefer to reproduce it in stereotype, cast clectrotype, or by other
method, and from any of these to print in the usual manner.