Improvements relating to the Production of Coloured Photographs, and to Apparatus for Viewing the same.
Year: 1899

page_text: Date of Application, 2nd Mar., 1899-Accepted, 29th July, 1899
COMPLETE SPECIFICATION.
Improvements relating to the Production of Coloured Photographs,
and to Apparatus for Viewing the same.
I, ROBERT WILLIAMS WOOD, of No. 237, Langdon Street, Madison, Wisconsin,
United States of America, Scientist, do hereby declare the nature of this inven-
tion and in what manner the same is to be performed, to be particularly described*
and ascertained in and by the following statement:―
My invention consists in a method of producing photographs in color by means
of a diffraction grating of varying grating space, the distance between the grating
lines varying with the color in different parts of the picture.
The method of my invention depends on the principal that the spectrum
produced by a diffraction grating in combination with a lens on which parallel
rays of light are directed is displaced with reference to the direct image of the
light source produced by the lens alone, and when viewed by an eye placed in
this spectrum the grating will appear illuminated with light of a color depending
on the part of the spectrum in which the eye is placed. If in any part of the
grating the spacing between the lines be different, that portion will have a
different color, since the spectrum formed by this portion is displaced relatively
to the other, and consequently light of a different color comes to the eye from
this area of the grating.
If a diffraction grating be made up of patches in which the spacing between
the lines is different, these patches will appear in colors depending on the dis-
tance between the lines, and a colored picture can be produced by a proper dis-
tribution of these patches, as I shall presently point out.
The accompanying drawings will serve to make my invention more readily
comprehended. In the drawings,
Figure 1 is a diagrammatic view, showing a diffraction grating of uniform
grating space, in connection with a lens, the projection of the spectra being
diagrammatically indicated;
Figure 2 is a similar view with the diffraction grating provided with varying
and overlapping grating space;
Figure 3 is a front view of the diffraction grating indicated in Figure 1, with
the lens in place;
Figure 4 is a front view of the diffraction grating indicated in Figure 2, with
the lens in place;
Figure 5 is a diagrammatic view of a multicolored object to be photographed,
the different colors being named on the drawing;
Figure 6 shows the distribution of the grating lines of a finished picture of
the object shown in Figure 5.
Figure 7, is a perspective view of an apparatus construction in accordance
with my invention.
Like letters indicate like parts in the different views.
Figure 1 and 2 are diagrams representing lenses in combination with diffrac
tion gratings of uniform and varying space. It will be understood that the
lines of the diffraction grating are in reality microscopic and invisible to the
Price S11

page_text: naked eye. The image of the light source is represented at c.. The spectra of
the colored rays resulting from the interference caused by the diffraction grating
is represented at d and d. In these latter spectra the colors will appear in their
natural order of red, green and blue, the red being most displaced.
If the grating be made up of two sets of lines of proper spacing, two over-
lapping spectra will be formed, the red of one falling on the green of the other,
and an eye placed at this point receives red light from one part of the grating
and green from another; consequently, the former appears red, the latter green.
If in any place these two spacings overlap, that is, if both sets of lines are
superimposed then the eye receives both red and green light from this portion,
which constantly appears yellow, since yellow is formed by a mixture of red and
green lights. We can now imagine a third spacing to be present in some part
of the grating, such that the blue of its spectrum falls on the spot where the red
and green of the other two are superimposed. The eye will now see this latter
area illuminated with blue light. If in any place all three spacings are present,
that is, if the three sets of lines are superimposed-then the eye will receive
red, green and blue light from the portion which will appear white in conse-
quence.
One way in which I have produced the colored photographs is as follows:
Three negatives of the object to be photographed are first taken through red,
green and blue screens in the usual manner, and from these positives on glass
are made. These positives are now flowed with a solution of gelatine and
bichromate of potash or any other suitable sensitizing solution and the three
diffraction gratings are then photographed by contact printing directly on the
film of the positive, the grating that is intended to give red light being im-
pressed on the positive made from the negative taken through the red screen,
the grating intended to give the green light being impressed on the positive
made from the negative taken through the green screen, and the grating intended
to give the blue light being impressed upon the positive taken through the blue
screen. A glass plate coated with bichromated gelatine or other suitable sensi-
tizing material is now exposed in succession under these three positives, proper
registration being secured by marks on the plates, and on being washed in warm
water, or otherwise developed, becomes the finished color photograph.
A modification of the process just described, but not differing in essential
fundamental principles is as follows: I provide a camera with three screens of
red, green and blue glass, on which the diffraction gratings have been ruled or
photographed. A sensitive plate of fine grain is exposed under the three screens
in succession; the screens being swung in front of and in contact with the
photographic plate. This plate when developed and viewed as I will describe
appears as a colored positive. To bring out the colors, I provide an apparatus
for combining the lens and the photograph and determining the directions from
which the photograph is viewed.
This consists of the apparatus shown in Figure 7, in which the lens a bis
located in front of a light, say, an incandescent light. Between the lens and
the light is located the color photograph. The screen g is made of opaque
material in which openings are provided for eye-holes. For convenience, I
provide adjustments for regulating the angle of the arm on which the lens,
photograph and eye-piece are mounted, and for regulating the relative positions
of the lens and screens as shown. The lens is made of such focus that correspond-
ing spectra formed on each side of the central uncolored image are at a distance
apart equal to the distance between the eyes. As the eye-holes coincide with the
superimposed portions of the spectra, the color may be seen by both
eyes at once.
"An arrangement is provided for altering the position of the holes and changing
the distance between them. The yellows of the picture are produced by the
mixture of red and green, and in those parts of the picture the two corresponding
gratings are superposed. White is produced in all parts of the picture where
all three of the gratings are impressed.

page_text: "
A contact print taken on a second glass plate coated with chrom-gelatine from
the original color photograph shows all the colors equally well, and is positive
also consequently, copies can be had in color as easily as blue prints," and
from each one of these others can be struck off, all being positive, such "colour
prints" being transparencies only, and not prints to be viewed by reflected light.
While I have described in detail one of the methods I follow in impressing a
colored picture upon the eye of the observer, numerous modifications in the
details of this process will suggest themselves to those skilled in the art. My
invention is not limited to this specific process which I have described. I believe
that it is broadly new with me to reproduce by photography the colors of the
object photographed through the instrumentality of a diffraction grating of
varying grating space.
Having now particularly described and ascertained the nature of my said in-
vention, and in what manner the same is to be performed, I declare that what I
claim is:-
1. The method of producing photographs in color, which consists in combining
positives of the objects photographed with diffraction gratings of varying grating
space, substantially as described.
2. The method of producing a photograph in color, which consists in directing
parallel rays of light through a positive, consisting of a diffraction grating of
variable spacing, and through a lens, and placing the eye in the spectrum of the
composite diffraction grating, substantially as described.
3. The method of producing a positive color photograph, which consists in
first taking negatives of the object to be photographed through red, green and
blue screens from these negatives producing positives on glass, covering these
positives with a sensitizing solution, photographing upon each positive a diffrac-
tion grating adapted to give its appropriate color, exposing a sensitized plate
in succession under these positives, and finally developing this plate, substan-
tially as described.
4. As a new article of manufacture, a colored photograph consisting of a
diffraction grating. of variable spacing, substantially as described.
5. As a new article of manufacture, a colored photograph consisting of a
diffraction grating of variable spacing arranged in patches corresponding in
shape and location to the shape and location of the colored areas of the object
photographed, substantially as described.
6. As a new article of manufacture, a colored photograph consisting of a posi-
tive on a glass plate composed of a diffraction grating and a photograph of the
object reproduced, substantially as described.
7. As a new article of manufacture, a diffraction varying grating space for
producing coloured photographs, the variations of spacing being such that the
red of the spectrum formed by one grating falls in the same place as the green
of the spectrum formed by the second grating, and the blue of the spectrum
formed by the third, substantially as described.
8. As a new article of manufacture, a colored photograph consisting of a
diffraction grating of a varying grating space, the variations of spacing being
such that the red of the spectrum formed by oue grating falls in the same place
as the green of the spectrum formed by the second, and the blue of the spectrum
formed by the third, substantially as described.
9. As a new article of manufacture, a colored photograph consisting of a
photographed diffraction grating of varying grating space, the variations of
spacing being such that the red of the spectrum formed by one grating falls in
the same place as the green of the spectrum formed by the second, and the blue
of the spectrum formed by the third, substantially as described.
10. An apparatus for viewing colored photographs, consisting of a stand, a
lens mounted thereon, means for holding the colored photograph adjacent to
said lens, an opaque screen, and an eye-hole therein adapted to be adjusted

page_text: to determine the direction from which the colored photograph may be viewed,
substantially as described.
11. An apparatus for viewing colored photographs, consisting of a stand, a
lens mounted thereon, adapted to corresponding spectra. at a distance between
the eyes, means for holding the colored photograph adjacent to said lens, an
opaque screen and eye-holes therein adapted to coincide with the superposed
portion of corresponding spectra formed by the lens, substantially as described.
Dated this 7th day of February 1899.
HASELTINE, LAKE & Co.,
45, Southampton Buildings, London, W.C.,
Agents for the Applicant.