Improvements in the Method of and Means for Rendering Photographic and other Pictures of Objects Visible in their Natural or in other Desired Colours.
Year: 1899

page_text: Date of Application, 2nd June, 1899
1000
1000
PROVISIONAL SPECIFICATION.
Improvements in the Method of and Means for Rendering Photographic
and other Pictures of Objects Visible in their Natural or in other
Desired Colours.
I, THOMAS THORP, of Whitefield, in the County of Lancaster, Architect and
Engineer, do hereby declare the nature of this invention to be as follows:-
When transparencies of photographs taken separately through red, green,
and blue-violet screens on isochromatic plates are viewed by transmitted light
in such a way that the three photographs appear superposed and only the res-
pective colour of each is transmitted to the eye, a picture of the object is seen
in its natural colours, as, for example, in the apparatus known as the Kromskop.
In carrying my invention into effect, at least three such separate photographs,
taken through coloured screens, and transparencies, are likewise necessary, but
I do not limit myself to this or any number of photographs as, for certain
purposes, more are advantageous.
These transparencies are only used however for printing other diffraction"
transparencies, the following manner of performing the operation being a con-
venient one.
A glass or other suitable transparent plate is coated with a sensitive film of
bichromated gelatine having a small percentage of glycerine added.
On this film is mounted a celluloid or other suitable replica of a diffraction
grating of preferably from 10,000 to 40,000 lines to the inch, the ruled side being
in contact with and preferably impressed into the gelatine film.
One of the original transparencies being now laid over the mounted plate and
exposed to sunlight or other suitable source of light, the portions of the gelatine
film under the clear parts of the transparency will be rendered more insoluble in
water than those parts under the opaque portions.
The grating film being now detached or dissolved away by a solvent having
little or no effect upon the gelatine, such as acetone, and the plate washed in
water, the reproduction of the grating is found upon the gelatine, varying in
its diffractive properties according to the proportion of light which each portion
bas received through the transparency.
In making these diffraction transparencies from the different original isochro-
matic transparencies, the lines of the grating are placed in each of them at
a different angle to the picture or design, which latter need not necessarily be
a photographic transparency, so that each diffraction transparency is differently
lined from the others.
The three or more, or in the case of designs where natural colours are not
required, two diffraction transparencies thus obtained are now preferably and
permanently superposed and when viewed or projected in a suitable manner,.
either by reflection or transmission are seen in colours. In the case of viewing,
preferably the first order of spectra from transmitted light is used and brought
to a focus at the eye by means of a lens placed immediately above the transparency

page_text: when the picture is in good definition as seen by an eye lens such as is used in
the stereoscope, each transparency being illumined only by direct or reflected
light at a right angle to the direction of the lines upon it, the actual light
being screened from the eye, the picture is seen uniformly coloured according to
the portion of the spectrum yielded by the grating of the picture and to the
position of the light, and when the lights or mirrors reflecting the light are
moved into such a position that the diffracted pencils from each transparency are
of the same colour as the screens through which the original photographs were
taken, the picture appears in its natural colours.
1510
In the case of the photographed object being a design or where a design is
specially prepared as, a transparency it is, clearly manifest that from one to a
considerable number may be used & that an unlimited variation and combination
of colours may be produced by the means above described.
"In lieu of using the gelatine diffraction transparencies made by this process,
celluloid replicas of them may be made, mounted and superposed in the manner
adopted for the gelatine transparencies.
Dal
TALE
1000
THOMAS THORP,
Applicant.
Improvements in the Method of and Means for Rendering Photographic
and other Pictures of Objects Visible in their Natural or in other
Desired Colours.
I, THOMAS THORP, of Whitefield, in the County of Lancaster, Architect and
Engineer, do hereby declare the nature of this invention and in what manner
the same is to be performed to be particularly described and ascertained in and
by the following statement:-
.
When transparencies of photographs taken separately through red, green
and blue violet screens on isochromatic plates are viewed by transmitted light
in such a way that the three photographs appear superposed and only the res-
pective colour of each is transmitted to the eye, a picture of the object is seen
in its natural colours as for example in the apparatus known as the Kromscop
For the purpose of transmitting only the respective colour of each of the
transparencies to the eye, it has been proposed to impress by means of photo-
graphy diffraction gratings of different spacing for each colour upon the respective
transparency, and illuminate them in combination with a lens by parallel rays of
light directed upon them from one direction, the different spacing for each colour
displacing the spectrum formed by the respective diffraction grating to a different
extent so that the spectra overlap, and if the eye is placed at a point where the
red of the spectrum from the. transparency taken through the red screen, the
green of the spectrum from the transparency taken through the green screen, and
the blue of the spectrum from the transparency taken through the blue screen
coincide, the photographed object will appear in its natural colours.
My improvements in the method of and means for rendering photographic and
other pictures visible in their natural or other colours consist chiefly in producing
diffraction transparencies from isochromatic photographic transparencies said dif-
fraction transparencies having gratings of the same spacing for all colours but
the lines of the grating placed at a different angle for each different colour, and
rendering them visible in the respective or any other colour by illuminating them
from different points, the positions of which are in planes perpendicular to the

page_text: lines of the gratings on the respective transparency but can be varied to alter
the angle of incidence of the rays, so as to obtain spectra overlapping and at the
same time crossing each other; and in the method of producing such diffraction
transparencies from photographs and for some purposes without the aid of
photography.
On the sheet of drawings appended hereunto Figures 1 and 2 show a diagra-
matic view of the apparatus employed for rendering the diffraction transparencies
visible in various colours in elevation and plan.
Figures 3, 4, and 5 diagrams of the positions of the spectra for viewing the
objects photographed in their natural or other colours.
Figure 6 shows a design in colours, Figures 7, 8 and 9 the three diffraction
transparencies produced from photographs through, say, green, red and blue
screens, and Figure 10 the three transparencies superposed.
In carrying my invention into effect in the case of natural objects to be
rendered visible in their natural colours at least three separate photographic
negatives taken through coloured screens and positive transparencies printed
from them are necessary, but I do not limit myself to this or any number of
such photographs or transparencies as for certain purposes more are advantageous.
These transparencies, however, are only used for printing other diffraction trans-
parencies, the following manner of performing this operation being a convenient
one.
A glass or other suitable transparent plate is coated with a sensitive film of
bichromated gelatine which is kept in a somewhat soft state until exposed to light
by the addition of a small percentage of some suitable substance, such as
glycerine. On this film is mounted a celluloid or other suitable replica of a
diffraction grating of preferably from 10,000 to 40,000 lines to the inch, the
ruled side being in contact with and preferably impressed into the gelatine film,
so as to produce the grating lines on the film by mechanical action.
One of the original isochromatic transparencies being now laid over the plate
prepared as aforesaid and exposed to sunlight or other suitable, source of light,
the portions of the gelatine film under the clear parts of the transparency will
be rendered more insoluble in water than those parts which are under the opaque
portions of the transparency. The celluloid or other grating being now detached
or dissolved by a solvent having little or no effect upon the gelatine, such as
acetone, and the plate washed in water, the reproduction of the grating is found
upon the gelatine, varying in the intensity of its diffractive action according
to the proportion of light each part has received through the transparency.
In making these diffraction transparencies from the different original isochro-
matic transparencies, the lines of the grating are placed in each of them at a
different angle to the picture, so that each transparency is lined in a different
direction from the others, all the gratings, however, having the sam
same spacing,
which preferably is as fine as possible.
In order to make this method of preparing the diffraction transparencies
perfectly clear, I will now refer to the drawings. Figure 6 represents a coloured
plaque or design to be photographed and rendered visible in colours, R denoting
red, W white, G green, B blue, Y yellow, and V violet. Of this plate three
negatives are taken through green, red and blue screens and positives printed
on glass or other transparent plates in the ordinary way. It is obvious that in
these positives only those parts of the plaque will be quite clear that contain the
pure colour corresponding with that of the respective screen, and more or less
clear in the parts of a colour into the composition of which the colour of the
screen enters, and be opaque on those parts the colour of which does not contain
the colour of the screen. Thus in the transparency taken through the green
screen, the parts marked G on Fig. 6 will be clear, and those marked W and Y
more or less so, while the rest will be opaque.
When this transparency is
placed upon the plate coated with a sensitive film of bichromated gelatine, into
which a replica of a diffraction grating has ben impressed, and exposed to light,

page_text: as described above, the parts marked G, W and Y on Figure 6 will transmit
light and the bichromated film be rendered more or less insoluble while under
the other parts it will remain soluble and after being washed a lined transparency
as shewn by Figure 7 will be obtained, the grating lines on this transparency
being placed say, horizontally as indicated.
In the same way the diffraction transparency obtained from the transparencies
taken through the red screen will be as represented by Figure 8, the celluloid
replica of the diffractive grating being in this case impressed upon the bichromated
film at an angle to the horizontal as shewn, the angle of the lines being preferably
10 degrees or less, but shewn exaggerated on the drawing for the sake of
clearness.
The diffraction transparency obtained from the transparency taken through the
blue screen will be represented by Figure 9, the diffraction grating being in
this case impressed upon it at an angle inclined to the horizontal in the opposite
direction to that used for the transparency Figure 8.
If more than three transparencies obtained through other coloured screens are
used, the lines on the diffraction transparencies made from them are preferably
placed at intermediate angles corresponding to the position of the respective
colour in the spectrum.
The three diffraction transparencies, Figure 6, and 8, hereinafter called the
green, red and blue plate respectively, are now preferably permanently super-
posed with the picture or image coinciding, as shewn on Figure 10, and when
viewed or projected in a suitable manner either by reflection or transmission are
seen in colours; and where the isochromatic photographs are taken from natural
objects, with the natural differences of light and shade.
For the purpose of viewing, preferably the first order of spectra from trans-
mitted light is used and brought to a focus at the eye by means of a lens placed
immediately above the transparency and when the picture is in good definition as
seen by an eye lens such as is used in the stereoscope, each transparency being
illuminated only by direct or reflected light in a plane perpendicular to the
direction of the lines upon it while the actual light is screened from the eye,
the picture on each transparency is seen uniformly coloured according to the
portion of the spectrum yielded by the grating, and when the lights or mirrors
reflecting the light are moved into such positions that the diffracted pencils from
each transparency transmitted to the eye are of the same colour as the screens
through which the original photographs were taken, the picture appears in its
natural colours.
By Figures 1 and 2 an apparatus suitable for viewing is represented diagram-
matically in elevation and plan.
In this apparatus the points of illumination, lenses and images on the trans-
parencies are duplicated so as to obtain the respective spectra and images at two
eye slits for the purpose of showing the photographed object stereoscopically.
On the drawing A represents a Welsbach incandescent burner from which the
light falls through slits upon two totally reflecting prisms B, which reflect the
rays of light to the reflectors M. Instead of the burner A and prisms B, in some
cases two incandescent filaments in the position of the prisms may
be used with advantage. The light from the mirrors falls upon the combined
diffraction transparencies P and passes through the lens L, and the picture is
viewed through the stereoscopic lenses L' and narrow eyeslits E. C is a screen
to shield the transparencies from the light of the burner.
For the purpose of causing the rays of light to fall on the respective diffraction
transparencies lined with gratings of uniform space but different inclinations to
the picture, in a plane perpendicular to the inclination of the lines, and to vary
the angle of incidence, the reflectors M are attached to the surface Q of an
ellipsoid of revolution, the major axis of which is in the line of the reflecting
point of the respective prism B and the centre of the lens L, which are in the
foci of the ellipse the rotation of which round the axis forms the ellipsoid. It is

page_text: evident that the light rays from the prism will be reflected to the centre of the
lens in any position of the reflectors M. Slots radiating from the axis are formed
in the surfaces Q so as to vary the position of the mirrors M and the angle of
incidence. The inclination of these slots to the vertical is the same as the
inclination of the grating lines to the horizontal, so that the rays B, M' O are
in a vertical plane perpendicular to the lines on the green plate, the rays B-M² O
in a plane perpendicular to the lines on the red plate, and the rays B M³ O
perpendicular to the lines on the blue plate. The three gratings diffract the rays
transmitted by the mirrors into spectra in the same planes as the rays, and if the
respective angle of incidence is so arranged by shifting the mirrors that the
green part of the spectrum S, Figure 3 formed by the green plate, the red part
of the spectrum S2 formed by the red plate, and the blue part of the spectrum S
formed by the blue plate fall upon the eyeslit, the photographed object will be
seen in its natural colours, the eyes being preferably placed at a short distance
from the eyeslits.
If the position of the mirrors is changed, the colour recived into the eye from
the different plates will be changed. By placing the mirrors M² and M³ into
the line of mirror M' for instance, the green part of the three spectra will be
transmitted through the slit, as represented by Figure 4, and the object will
appear all green; by shifting the three mirrors to the top, it will be shewn all
red, and by shifting the three mirrors to the bottom it will appear all blue. By
shifting the mirrors M and M2 to the bottom and the mirror M³ to the top, the
blue parts of the spectra from the green and red plate and the green part of the
spectrum from the blue plate will fall into the eye, as represented by Fig. 5, so
that the green and red portion of the photographed object will appear blue, and
the blue parts green. It will be evident that by altering the positions of the
mirrors any part, of each spectrum can be made to fall into the eye, and any
variety of different colourings besides the natural colours rendered visible.
In some cases the mirrors M may be replaced by incandescent filaments move-
able in the same way, and the prisms and burners or other source of light omitted.
In the case of flat objects such as designs of wall papers for instance or where
a stereoscopic effect is not to be produced, of course only one set of reflectors and
one source of light and diffraction transparent photographs are required.
In the case of designs in two colours of course only two diffraction trans-
parencies and two reflectors will be wanted. The diffraction transparencies for
such designs and the like can be produced without the aid of photography, by
placing a celluloid replica of a diffraction grating over the design or drawing it
upon such replica, and painting for each colour the parts having a different colour
with varnish to fill up the grating spaces, placing the grating lines at a different
angle for each colour. Thus the three plates, Figures 7, 8 and 9, can be obtained
by placing three celluloid gratings over the design Figure 6 at the respective
angles and painting the white parts in Figures 7, 8 and 9 with transparent varnish,
which when superposed and inserted into the apparatus will show the design in
its original or any other colours in the same way as the gelatine diffraction
transparencies obtained from photographs taken through isochromatic screens in
the manner hereinbefore described. The transparencies may likewise be produced
by printing on the celluloid gratings with varnish or like filling and making
transparent replicas of them in the manner hereinafter described.
It is obvious that where the photographed object is a design or where a design
is specially prepared as a transparency in the manner herein last described, from
one to a considerable number of transparencies with gratings of the same spacings
but different inclinations may be used and that an unlimited variation and com-
bination of colours may be produced by the means herein before described.
Instead of using the gelatine diffraction transparencies obtained from the
photographs, or those obtained directly without the aid of photography, by the
processes herein before described, celluloid replicas of them may be made, mounted

page_text: and superposed in the manner adopted for the gelatine transparencies. This
can be done by smearing the original with a thin oil, such as watchmakers oil,
and pouring the celluloid solution upon it; when set the replica can be readily
pulled off.
Instead of allowing the coloured rays from the diffraction transparencies to
fall into the eye, they may be thrown upon a screen in the well known manner.
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:-
1. The manufacture and use of two or more photographie or other diffraction
transparencies of the same object having the same grating space but different
inclinations of the grating lines on each transparency, for the purpose of rendering
photographs or other pictures visible in different colours, substantially as herein-
before described.
2. The method of preparing photographic diffraction transparencies for the
purpose of rendering photographs visibie in the natural colour of the object or in
other colours which method consists in first taking negatives of the object through
red, green and blue or other coloured screens and printing positive transparencies
from them; coating transparent plates with bichromatic gelatine kept moist by
the addition preferably of glycerine impressing celluloid replicas of a diffraction
grating upon said coated plates placing each of said positives upon a separate
such coated plate and celluloid grating, exposing the same to the action of
sunlight or other suitable light, removing or dissolving the celluloid replica of
the grating and washing the plate; the celluloid gratings having all the same
grating space but being impressed upon the bichromated gelatine at a different
inclination to the picture for each of the said positives; substantially as herein-
before described.
3. The manufacture and use of diffraction transparencies made by the method
specified in the last preceding claim and as hereinbefore described and for the
purpose set forth.
4. The method of rendering photographs of objects visible in their natural or
other colours which consists in illuminating photographic transparencies having
diffraction gratings of the same grating space but a different inclination of the
grating lines prepared from each of the positives obtained through differently
coloured screens and superposed, by direct or transmitted light from different
points, one of said points being situated in each plane perpendicular to the inclina-
tion of the grating lines on the different transparencies and capable of being
shifted in such planes to alter the angle of incidence of the light upon the
respective diffraction transparency; said transparencies being placed in front
of a lens and viewed through a stereoscopic lens and slit, substantially as herein-
before described and illustrated by the drawings.
5. For the purpose of carrying out the method of rendering photographic or
other diffraction transparencies visible in colours specified in the 4th Claim and
as hereinbefore described, the arrangement of reflectors or incandescent filaments
moveable on the inner surface of an ellipsoid of revolution in planes passing
through its axis, said axis being central with that of the lens placed in front
of the transparencies, the source of light in the case of reflectors and the lens
being in the foci of the generating ellipse, substantially as herein before described
and illustrated by the drawings.
6. The method of preparing diffraction transparencies from designs by painting
or printing on each the part not to be rendered visible with varnish or the like,
substantially as herein before described and illustrated by the drawings.
7. The use of diffraction transparencies of designs prepared as specified in the
preceding claim, with a different inclination but uniform spacing of the grating
lines for each part of the design having a different colour, for the purpose of

page_text: rendering the design visible in its original or other colours substantially as
herein before described and illustrated.
8. The manufacture and use of celluloid replicas of diffraction transparencies
substantially as hereinbefore described.
Dated the 1st day of March 1900
R. J. URQUHART, C.E.,
Chartered Patent Agent, Manchester & Liverpool.