IMPROVEMENTS IN PHOTOGRAPHIC ENGRAVING
Year: 1879

page_text: LETTERS PATENT to Joseph Wilson Swan, of Newcastle on Tyne, in the
County of Newcastle, Chemist, for the Invention of "IMPROVEMENTS IN
PHOTOGRAPHIC ENGRAVING."
Sealed the 20th January 1880, and dated the 22nd July 1879.
PROVISIONAL SPECIFICATION left by the said Joseph Wilson Swan at the
Office of the Commissioners of Patents on the 22nd July 1879.
JOSEPH WILSON SWAN, of Newcastle on Tyne, in the County of Newcastle,
Chemist. IMPROVEMENTS IN PHOTOGRAPHIC ENGRAVING."
"
The first part of my Invention consists in the employment of a new and exceed-
ingly rapid means of producing a photographic image in intaglio or relievo.
Instead of the materials hitherto used for this purpose I employ a solution of
gelatine, with which bromide of silver is intimately mixed in the form of a paint
or emulsion. This mixture or emulsion I prepare without exposure to chemically
active light, and I apply it as a coating to glass or other suitable surface. Such
coated surface I expose to the action of light in such a manner as to produce upon
it a developable image of the object of which an intaglio or relievo is required to
be made. The exposure of light may be effected through the medium of a camera
obscura or an instrument on that principle, or the action of light may in some cases
advantageously take place in a more direct manner without the intervention of a
lens, namely, by the direct exposure to light of the emulsion coated plate while
covered with a negative or positive transparency of the object of which an intaglio
or relievo is required to be made. After exposure to light of the said emulsion
coated plate in either of the manners indicated the image is developed in a photo-
graphically dark room in the manner usual in developing photographs. The
developing solution I prefer to use for this purpose is a solution of pyro-gallic acid,
to which is added a certain proportion of bromide of ammonium and of liquor
ammonia; but I do not limit myself to the use of these materials for developing
the image. The bromide of ammonium is non essential, but I prefer to use it; the
ammonia may be replaced by potash or soda. The image having been developed
in the manner described I place it in water of a temperature of 100° Fahrenheit
or thereabouts; or I subject it to heat while moist, so as to produce a swelling of

page_text: the-parts-not-acted upon by the light, or least acted upon during the exposure in
the camera obscura or printing frame which produced the developable image. The
character of the intaglio or relievo image depends on many attendant circumstances,
-among-which may be mentioned the thickness of the gelatine coating, the depth to
-which-the light has penetrated through it, and the temperature to which it is sub-
jected while wet. The addition to the gelatine emulsion of chrome alum or other
substances having-an-analogous-hardening effect upon gelatine, or having the
effect of rendering it insoluble or less soluble in water, is also an important means
of influencing the quality of the resulting intaglio or relievo image tending to the
production of crispness and solidity in the image and to the repression of a too.
great tendency in the gelatine to swell, and the control of the character of
reticulation producible in those parts of the film of gelatine which have not been
completely penetrated through the entire thickness of the stratum of gelatine, but
which have yet been acted upon to some degree. Another mode of developing
relief in a plate on which an image has been produced in the manner described is
as follows:-After developing the image instead of subjecting it to the action of.
warm water, or otherwise exposing it while in a state of humidity to heat, I allow
the image to become completely dry, and I then apply to it by a brush or pad, or
in any other convenient manner, strong acetic acid, so as to dissolve the parts which
have been jointly acted upon by light and the chemicals employed. By successive
applications of the acid and interim drying a sufficient degree of relief may be pro-
duced to be useful in printing processes. This last named mode of operating is
restricted to the representation of that class of objects in which there is no half tone
but only one grade or tint of color. The first described method is not thus
restricted but is equally applicable to cases where the object depicted is represented
by means of varying but unbroken graduations of shading. I utilize the relievo
or intaglio images produced by the methods described by in some cases taking
a cast or mould in plaster of Paris, wax, gutta percha, or any other suitable
mould compound, and afterwards taking an electrotype or a cast in type metal
or fusible metal from these; or in certain cases I take an electro-type direct from
the relievo or intaglio image in gelatine, and use this electrotype as the printing
plate. In the case of the acid produced relievo or intaglio I sometimes use lead or
other soft metal pressed by a press into close contact with the gelatine image in a
dry state, so as to produce a counterpart impression.
The second part of my Invention consists of new and improved means of
adapting photography to typographic printing, in the case more particularly of that
class of objects which if photographed in the ordinary way would yield pictures
possessing half tone or more or less unbroken gradations of light and shade. Such
objects are, for example, landscapes, portraits from life, paintings, and solid objects
generally, or ordinary photographic representations of them. The difficulty not
hitherto completely overcome in adapting photography to the production of typo-
graphic blocks of such objects as those described has consisted in the incapability.
of the typographic method of printing to represent light and shade in gradation
of a continuous character, such as is produced in photographs of natural objects or
paintings. In order therefore to enable a photograph of such objects to be printed
typographically, so as to render the lights and shades of the objects, it is necessary
to break up the continuous gradation of light and shade in the original photograph
picture or other object into line or stipple, so as to give it a discontinuous character
equivalent in pictorial effect to the continuous graduation of light and shade of the
original object. The same requirement, to modify the character of the light and
shade, generally exists although in a less degree in connection with the adaptation
of photography to the copper plate or intaglio method of printing and to litho-
graphy, and my mode of procedure in obtaining the required change of character
in photographs from continuous to discontinuous gradation is applicable with
suitable modifications to these methods of printing as well as to the typographic
method. The chief feature of my Invention in effecting the conversion in question
consists in a peculiar mode of using screens or gratings, either in conjunction with

page_text: the sensitive plate on which the primary photographic image of the object is pro-
duced or in conjunction with a previously produced photograph of the object. The
screen or grating may conveniently consist of a plate of glass or mica or of a film
of collodion gelatine, or other transparent pellicular material, bearing a series of fine
transparent lines on an opaque ground; these may be produced either by a ruling
machine or photographically. The width and closeness of the lines forming the
gratings are varied in accordance with the nature of the object in the representation
of which they are to be used; I use such gratings in one or other of the following
ways:
1st way. I place a grating in front of and in contact with the sensitive plate
while it is being exposed in a camera obscura to the action of the light reflected by
the object to be photographed, and I shift the grating into several different
positions during the exposure, shifting it so that the lines in one position shall
intersect the lines in another position. I generally allow the grating to remain
longer in one position than in another, so that the crossings are both more numerous
and of greater breadth in the shades of the picture than in the lights. I sometimes
also impart motion to the grating during exposure, the motion being in the plane
of the face of the grating perpendicular to its lines and equal, or nearly equal, in
extent to the space between two consecutive lines; if the lines are 01 of an inch
apart the movement does not exceed 01 of an inch. I generally prefer to effect
the transit motion of the screen as described in varying intervals or continuously,
but varying the rate of motion so as to produce a stronger impression of lines while
the screen is in one part of its transit than in another.
2nd way. Instead of placing the grating in contact with the sensitive plate I
place it in contact with a negative or positive transparency, generally a photograph
of the object to be represented, and in this case as in the former I move the grating
into various positions, so that I produce a series of line crossings; or I employ the
transit movement as above described, and I sometimes combine the transit move-
ment with the shifting of the grating, so as to produce line crossings.
3rd. way. Instead of employing the camera obscura I sometimes produce the
required effect by operating in the manner usual in photographic printing by super-
position, in which light is transmitted by a transparent positive or negative image
of the object to the sensitive surface pressed into close proximity with it. The
grating is in this case formed upon a thin film or pellicle, and is interposed between
the said positive or negative transparent image and the sensitive surface destined
to receive the photographic impression.
A suitable pressure frame is employed to press the grating closely between the
sensitive surface and the negative or positive transparency, and is so arranged as
to allow of its being opened to a sufficient extent to permit the shifting of the
screen into various positions without altering the relative position of the said
negative or positive transparency and the sensitive receiving surface. In using the
gratings in the last named manner I not only vary their position several times
during the production of one print but I also vary the degree of exposure for each
different position of the grating, so as to produce a stronger impression of the
lines and a greater number of line crossings in the shades of the picture than in
the lights; sometimes I also vary the character of the grating for the different
exposures. The photographic image produced in the various ways above described
corresponds in character to a cross hatched engraving or pen and ink drawing, and
is either itself, or after being copied by photography, adaptable by suitable and
well known methods to photo-typography, to photographic engraving, and to
photo-lithography.

page_text: -the said Joseph Wilson Swan_in the Great Seal Patent Office on the 22nd
January 1880.
JOSEPH WILSON SWAN, of Newcastle on Tyne, in the County of Newcastle,
Chemist. IMPROVEMENTS IN PHOTOGRAPHIC ENGRAVING."
"
The first part of my Invention consists in the employment of a new and exceed-
ingly rapid means of producing a photographic image in intaglio or relievo. Instead
of the materials hitherto used for this purpose I employ a solution of gelatine with
which bromide of silver is intimately mixed, in the form of a paint or emulsion.
Great latitude is allowable in the manner of preparing the sensitive compound of
gelatine and bromide of silver, both as regards the proportions of the materials
composing it and also as regards the mode of combination. I prefer to form the
said compound as follows:-I take of gelatine 15 parts by weight, of bromide of
potassium 8 parts by weight, of nitrate of silver 10 parts by weight, of water 200
parts by weight; I dissolve the gelatine and bromide of potassium in 100 parts of
the water at 100° Fahrenheit, and I dissolve the nitrate of silver in the remaining
100 parts of water at 100° Fahrenheit. I then add the nitrate of silver solution to
the gelatine and bromide of potassium solution; this addition is made gradually,
and the compound is stirred or shaken during the addition. I allow the emulsion
thus formed to become cold and to set into the state of a stiff jelly, and in that state,
but broken up into small masses, I wash it with cold water to remove the nitrate
of potash formed as a bye product. I then drain away as much as possible of the
adherent water, and bring the temperature to 110° or thereabout; in forming and
using this mixture or emulsion I am careful to avoid any exposure of the same, or
of plates coated with it, to chemically active light, except such as is employed to
produce the required image. This seclusion from diffuse light is necessary from that
point of the process at which bromide of silver is formed to that other point at which
the bromide of silver is dissolved. I apply the emulsion warm as a coating to glass
or other suitable surface. Such coated surface I expose to the action of light in such
a manner as to produce upon it a developable image of the object of which an
intaglio or relievo is required to be made. The exposure to light may be effected
through the medium of a camera obscura or an instrument on that principle, or the
action of light may in some cases advantageously take place in a more direct manner
without the intervention of a lens, namely, by the direct exposure to light of the
emulsion, coated plate while covered with a negative or positive transparency of the
object of which-an-intaglio-or-relievo-is required to be made. After exposure to
light of the said emulsion coated plate in either of the manners indicated the image
is developed in a photographically dark room in the manner usual in developing
photographs. The developing solution I prefer to use for this purpose is a solution
of pyrogallic acid to which has been added a certain proportion of bromide of
ammonium and of liquor ammonia. It is constituted as follows:-'
-Water 1,000
parts by weight, pyrogallic acid 5 parts by weight, bromide of ammonium 5 parts
by weight, liquor ammonia (880 s.g.) 5 parts by weight. I do not limit myself
exclusively to the use of these materials or proportions for developing the image.
The bromide of ammonium is non essential, but I prefer to use it, and the ammonia
may be replaced by potash or soda. The image having been developed in the
manner described I place it in water at a temperature of 90° Fahrenheit or there-
about, or I subject it to heat while it is more or less moist, so as to produce a swell-
ing of the parts not acted upon by the light, or least acted upon during the exposure
in the camera obscura or printing frame which produced the developable image.
The character of the intaglio or relievo image depends on many attendent circum-
stances, among which may be mentioned the thickness of the gelatine coating, the
depth to which the light has penetrated through it, and the temperature to which

page_text: it is subjected while wet. The addition to the gelatine emulsion, or the application
to plates coated with it of a solution of chrome alum, common alum, tannin, or other
substance having an analogous hardening effect upon gelatine, or having the effect
of rendering it insoluble or less soluble in water, is also an important means of
modifying the character of the resulting intaglio or relievo image, tending to the
production of crispness and solidity in the image, diminishing the swelling of the
gelatine, and controlling the character of the reticulation producible in those parts
of the film of gelatine which have not been completely penetrated through the entire
thickness of the stratum of gelatine, but which have yet been acted upon to some
degree. Another mode of developing relief in a plate on which an image has been
produced in the manner described is as follows:-After developing the image, instead
of subjecting it to the action of warm water, or otherwise exposing it while in a
state of humidity to heat, I allow the image to become completely dry, and I then
apply to it, by a brush or pad or in any other convenient manner, strong acetic acid,
so as to dissolve the parts which have been jointly acted upon by light and the
chemicals employed. By successive applications of the acid and interim drying a
sufficient degree of relief may be produced to be useful in printing processes. This
last named mode of operating is restricted to the representation of that class of
objects in which there is no half tone, but only one grade or tint of colour. The
first described method is not thus restricted, but is equally applicable to cases where
the object depicted is represented by means of varying but unbroken gradations of
shading. I utilise the relievo or intaglio images produced by the methods described
by in some cases taking a cast or mould in plaster of Paris, wax, gutta percha, or
any other suitable mould material, and afterwards taking an electro type or a cast
in type metal or fusible metal from these first casts; or in certain cases I take an
electro type direct from the relievo or intaglio image in gelatine, and use this electro-
type as the printing plate. In the case of the acid produced relievo or intaglio I
sometimes use lead or other soft metal, pressed by a press into close contact with
the gelatine image in a dry state, so as to produce a counterpart impression.
The second part of my Invention consists of new and improved means of
adapting photography to typographic printing in the case more particularly of the
pictorial representation of that class of objects which if photographed in the
ordinary way would yield pictures possessing half tone, or more or less unbroken
gradations of light and shade; such objects are, for example, landscapes, portraits
from life, paintings, and solid objects generally, or ordinary photographic repre-
sentations of them. The difficulty not hitherto completely overcome in adapting
photography to the production of typographic blocks of such objects as those
described has consisted in the incapability of the typographic method of printing
to represent light and shade in gradation of a continuous character, such as is
produced in photographs of natural objects or paintings. In order therefore to
enable a photograph of such objects to be printed typographically so as to render
truly the lights and shades of the object, it is necessary to produce a picture in
which the continuous gradation of light and shade in the original photograph
picture or other object is broken up into line or stipple in such a manner as to
give shading of a discontinuous character equivalent in pictorial effect to the con-
tinuous gradation shading of the original object. The same requirement to modify
the character of the light and shade generally exists, although in a less degree, in
connection with the adaptation of photography to the copper plate or intaglio
method of printing and also to lithography, and my mode of procedure in obtaining
the required change of character in photographs from continuous to discontinuous
shading is applicable with suitable modifications to these methods of printing as
well as to the typographic method. The chief feature of my Invention for effecting
the conversion in question consists in a peculiar mode of using screens or gratings
either in conjunction with the sensitive plate on which the primary photographic
image of the object is produced, or in conjunction with a previously produced
photograph of the object. The screen or grating may conveniently consist of a
plate of glass or mica, or of a film of collodion gelatine or other transparent

page_text: pellicular-material-bearing a series of fine transparent lines on an opaque ground.
These gratings may be produced either by means of a ruling machine-and-cutter
operating upon a plate of-silvered-glass or photographically (by any of the well
known-processes of photography) by producing a very dense and pure negative
image of parallel wires-or-black-lines on a white or transparent ground. The
width and closeness of the lines forming the gratings produced in the manner
described are varied in accordance-with--the-nature of the object in the repre-
sentation of which they are to be used. I use such gratings in one or other of the
following ways: First way I place a grating in front of and in contact with the
sensitive plate, while it is being exposed in a camera obscura to the action of the
light reflected by the object to be photographed, and I shift the grating into
several different positions during the exposure, shifting it so that the lines pro-
duced in one position shall intersect the lines produced in another position. I
generally allow the grating to remain longer in one position than in another, so
that the crossings may be both more numerous and of greater breadth in the lights
of the picture than in the shades. I sometimes also impart motion to the grating
during the exposure, the motion being in the plane of the face of the grating
perpendicular to its lines, and equal or nearly equal in extent to the space between
two consecutive lines. If the lines are 01 of an inch apart, which is a spacing
commonly useful, movement does not exceed 01 of an inch. I generally prefer to
effect the transit motion of the screen as described in steps of varying time
intervals, or if continuously varying the rate of motion so as to produce a stronger
impression of lines while the screen is in one part of its transit than in another.
The effect of this operation is to produce a photograph of the object to which the
lens was opposed consisting of lines more numerous and broader jin those parts
corresponding with the lights of the object, and thinner and less numerous in those
parts corresponding with the shades of the object. This photograph may be
employed as a negative by transmitted light, or as a positive by reflected light, in
conjunction either with the process for producing intaglio or relievo herein before
described as the first part of my Invention, or in conjunction with the well
known process of producing intaglio and relievo by means of light acting upon
gelatine combined with bichromate of potash. The linear photograph may also be
utilised in conjunction with well known photo-etching processes, in which gelatine
and bichromate of potash or asphaltuni are the materials chiefly employed as
media for producing a reserve or resist of asphaltum or. printing ink, which
protects those portions of the plate to be etched against the action of the etching
acid. If the linear photograph be employed as a positive it must be produced
upon a dark ground, that is to say, the glass may be dark colored glass, or if not
dark it may be coated with a dark colored paint either before or after the photo-
graph has been produced upon-it,-or-the-plate. used may be of the kind known as
a ferrotype plate, and the photograph itself may with advantage be whitened by
the action of a solution of bichloride of mercury. Second way Instead of placing
the grating in contact with the sensitive plate, I place it in contact with a negative
or positive transparency, generally a photograph of the object to be represented,
and in this case as in the former I move the grating into various positions, so that
I produce a series of line crossings, or I employ the transit movement as above
described, and I sometimes combine the transit movement with the shifting of the
grating so as to produce line crossings. If in the foregoing operation a negative
has been employed then a linear positive image is produced, and I prefer to produce
this upon opal glass and to produce a linear negative from that, the same to be
used in the manner described under the previous heading. Third way: Instead of
employing the camera obscura I sometimes produce the required effect by
operating in the manner usual in photographic printing by superposition, in which
light is transmitted by a transparent positive or negative image of the object to the
sensitive surface pressed into close proximity with it. The grating is in this case
formed upon a thin film or pellicle, and is interposed between the said positive or
negative transparent image and the sensitive surface destined to receive the photo-

page_text: graphic impression. A suitable pressure frame is employed to press the grating
closely between the sensitive surface and the negative or positive transparency,
and is so arranged as to allow of its being opened to a sufficient extent to permit
the shifting of the screen into various positions without altering the relative. position
of the said negative or positive transparency and the sensitive receiving surface.
In using the gratings in the last named manner I not only vary their position
several times during the production of one print, but I also vary the degree of
exposure for each different position of the grating so as to produce in those cases in
which a negative is employed a stronger impression of the lines and a greater
number of line crossings in the shades of the picture than in the lights, and in those
cases where a positive transparency is employed I so shift the grating as to produce
a stronger impression of the lines and a greater number of line crossings in the
lights of the picture than in the shades. Sometimes I also vary the character of
the gratings employed to produce the different series of lines in one and the same
picture. The linear photographic image produced in the various ways above
described corresponds in character to a cross hatched engraving or pen and ink
drawing, and is either itself or after being copied by photography adaptable by
suitable and well known methods to photo-typography, to photographic engraving,
and to photo-lithography.
Having stated the nature of my Invention, and the manner in which the same is
to be carried into effect, I claim in connection with the first part of my
Invention,-
1st. The employment of bromide of silver in conjunction with gelatine as a
means of procuring photographic images in intaglio or relief.
2nd. I claim the application of the intaglio or relievo images formed in the
manner described to the production of printing blocks and plates.
3rd. I claim the particular mode of using screens or gratings described, so as to
produce photographs in which a continuous character of shading in the original is
represented by shading of a linear or discontinuous character in the copy.
4th. I claim the use of pellicular screens or gratings for the purpose and in the
manner herein described.
In witness whereof, I, the said Joseph Wilson Swan, have hereunto set my hand
and seal, this Twentieth day of December, in the year of our Lord One
thousand eight hundred and seventy-nine.
TACEDIT BUTT CONT CAT
CADDY WTI CON CUAT
JOSEPH
ATTILA NET LL