Improvements in the Manufacture of Selective Color Light Filters for Photo Optical Purposes.
Year: 1899

page_text: Date of Application, 15th June, 1899
Complete Specification Left, 12th Apr., 1900-Accepted, 14th July, 1900
PROVISIONAL SPECIFICATION.
Improvements in the Manufacture of Selective Color Light Filters for
Photo Optical Purposes.
I, GUSTAV SELLE, of Brandenburg, on the Havel, in the Empire of Germany,
Physician, do hereby declare the nature of this invention to be as follows:-
"
Photographic negatives representing the 3 primary color sensations are as is well
known, produced by exposing three sensitised plates behind transparent screens
called light filters," colored respectively blue-violet, green, and red, allowing
individually the passage to and impression on the negative of particular light rays
only. Since the proper and correct separation of the coloring of any object into
its primary color constituents depends entirely on these so called selective screens
their function is one of great importance. But such screens to accomplish effec-
tually the purpose for which they are intended must conform to certain conditions
on the fulfilment of which singly and jointly will depend their value. It is
essential, (1) that such screens shall represent an extremely thin homagenous
surface of uniform thickness and great transparency so that the light rays may
pass freely and without encountering variations in resistance such as would occur
if the surface to be penetrated were of unequal depth: (2) the coloring of the
screens must correspond to certain sections of the spectrum, i.e. the red filter must
cover the section from A to nearly D; the green filter the section from 1) to F;
and the blue filter the section from F to H: (3) the coloring must be perfectly
pure and uniform and of such nature and concentration as to embrace the whole
group of rays contained within its allotted section; (4) the colors must possess
extreme luminousness so that the intensity of the light rays shall not be impaired
otherwise the impression on the negative would suffer both in sharpness and
value. Light filters are made up of two elements. The coloring matter and the
medium which holds it and my object is to constitute and combine these in such
manner that they shall fully comply with the above enumerated conditions. Ere
this, screens have been made of tinted glass, or of tinted gelatine, varnish, normal
collodion or collodion treated with an acetate, or of a tinted fluid held within a
glass casing. Of these the gelatine screen proved the most serviceable but none
were free from some disadvantage that reacted on the quality of the ultimate
result for although the scientific principle of 3 color photography is simple, the
practice and failures of 30 years have proved that its translation into a practical
thing is entirely a matter of excellence of details. By reason of its purity and
transparency collodion tinted with proper coloring is particularly adapted for light
screens but in its normal condition it contracts so strongly upon drying that a
net like surface results which has a disturbing effect on the sensitive plate. I
found that this can be obviated if normal collodion be reduced by a suitable
attenuant until the viscosity and molecular attraction is enfeebled to an extreme
degree without at the same time destroying cohesion. I achieve this by treating
normal collodion with an excess of ether or other substances having the same
attributes. Taking for instance a 3% collodion I dilute it with about 50% of

page_text: ether. With such solution I incorporate colors combining capacity of concentra-
tion and correctness of tint with extreme purity transparency and luminousness.
For the blue filter I use a mixture of blue and red, gentiana blue and fuchsin
or other colors having the same tints and attributes.
For the green filter I use a mixture of emerald green and auramin yellow or
other colors with the same tints and attributes; for the red filter I use a mixture
of fuchsin red and saffranin yellow or other colors having the same tints and
attributes; after covering glass plates with a layer of such tinted collodion by
flooding and pouring off the excess, the filters must be dried in a heated atmos-
phere, (say about 60° Celsius) to prevent irregularities in drying and a separation
or precipitation of the colors which would otherwise frequently take place.
Dated this 15th day of June 1899.
HERBERT HADDAN & Co.,
Agents to Applicant.
Improvements in the Manufacture of Selective Color Light Filters for
Photo Optical Purposes.
I, GUSTAV SELLE, of Brandenburg, in the Empire of Germany, Physician, 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 follow-
ing statement:-
Photographic negatives representing the three primary color sensations are,
as is well known, produced by exposing three sensitized plates, behind trans-
parent screens called "light filters," colored respectively blue-violet, green and
red, allowing individually the passage to and impression on the negative of par-
ticular light rays only. Since the proper and correct separation of the coloring
of any object into its primary color constituents depends entirely on these so-
called selective screens their function is one of great importance. But such
screens to accomplish effectually the purpose for which they are intended must
conform to certain conditions on the fulfilment of which singly and jointly will
depend their value. It is essential (1) that such screens shall represent an
extremely thin homogenous surface of uniform thickness and great transparency
so that the light rays may pass freely and without encountering variations in
resistance such as would occur if the surface to be penetrated were of unequal
depth; (2) the coloring of the screens must correspond to certain sections of the
spectrum, .e. the red filter must cover the section from A to nearly D; the
green filter the section from J) to F; and the blue filter the section from l' to H;
(33) the coloring must be perfectly pure and uniform and of such nature and con-
centration as to embrace the whole group of rays contained within its allotted
section (4) the colors must possess extreme luminosity so that the intensity of
the light rays shall not be impaired otherwise the impression on the negative
would suffer both is sharpness and value. Light filters are made up of two
elements, the coloring matter and the medium which holds it and my object is
to constitute and combine these in such manner that they shall fully comply with
the above enumerated conditions. Ere this, screens have been made of tinted
glass, or of tinted gelatine, varnish, normal collodion or collodion treated with
acetate, or of a tinted fluid held within a glass casing. Of these the gelatine
screen proved the most serviceable but none were free from some disadvantage
that reacted on the quality of the ultimate result for although the scientific
principle of three color photography is simple, the practice and failure of 30

page_text: years have proved that its translation into a practical thing is entirely a matter
of excellence of details. By reason of its purity and transparency collodion tinted
with proper coloring is particularly adapted for light screens but in its normal
condition it contracts so strongly upon drying that a net like surface results which
has a disturbing effect on the sensitive plate. I have found that this can be
obviated if normal collodion be reduced by a suitable attenuant until the viscosity
and molecular attraction is enfeebled to an extreme degree without at the same
time destroying cohesion. I achieve this by treating normal collodion with an
excess of ether or other substances having the same attributes. Taking for
instance a three per cent. collodion I dilute it with about 50 per cent. of ether.
With such solution I incorporate colors combining capacity of concentration and
correctness of tint with extreme purity, transparency, and luminosity. For the
blue filter I use a mixture of blue and red, gentiana blue and fuchsin or other
colors having the same tints and attributes.
For the green filter I use a mixture of emerald green and auramin yellow or
other colors with the same tints and attributes; for the red filter I use a mixture
of fuchsin red and saffranin yellow or other colors having the same tints and
attributes: after covering glass plates with a layer of such tinted collodion by
flooding and pouring off the excèss the filters must be dried in a heated atmos-
phere (say about 60 degrees Celsius) to prevent irregularities in drying and a
separation or precipitation of the colors which would otherwise frequently take
place.
Having now particularly described and ascertained the nature of the said
invention and in what manner the same is to be performed I declare that what
I claim is
In the manufacture of selective color light filters,
1. The medium for holding coloring matter, consisting of collodion treated to
excess with ether or other attenuant possessing same attributes.
2. The incorporation with the aforesaid or other equally suitable medium, of
coloring substances possessing individually and jointly the tints and attributes
of the colors herein described.
3. The method of drying collodion filters namely in a heated atmosphere as
and for the purpose described.
4. A screen for blue rays comprising blue and red coloring matter.
HERBERT HADDAN & Co.,
Agents to Applicant, 18, Buckingham Street, Strand, W.C., London.